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Claims  |
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What is claimed is:
1. A method of recording and/or reproducing a video signal and an
associated audio signal in/from a record carrier comprising: during
recording, encoding the video signal and the audio signal to form a first
and a second information signal respectively comprising information words
arranged in frames, each frame comprising a frame header and a data field,
a data field of a frame comprising a plurality of information words of the
video signal or an audio signal, the header indicating the information
signal to which the information words in the data field belongs; recording
the frames on the record carrier; during reproduction, reading the frames
from the record carrier and decoding said frames to obtain the video
signal and the associated audio signal, wherein for recording at least a
second audio signal associated with the video signal the second audio
signal is encoded to form a third information signal comprising
information words arranged in frames, wherein the frame headers of those
frames which comprise an encoded audio signal moreover indicate to which
of the two or more audio signals the information words in a data field of
a frame belong, wherein reference signals and additional frames are
recorded on the record carrier, which additional frames for each of the
two or more audio signals associated with a video signal contain time
information pertaining to the time interval between the instant at which a
reference signal is detected after read-out and the instant at which a
read-out video signal is to be displayed, and during reproduction the
reference signals and the additional frames are read from the record
carrier, the time information associated with one of the audio signals is
derived from an additional frame under the influence of a first control
signal and subsequently a second control signal is derived from the time
information thus derived and from a detected reference signal for
displaying a read-out video signal, and wherein only one of said audio
signals is selected and reproduced in response to a first control signal.
2. A method as claimed in claim 1, wherein the detected reference signal is
inserted in a sub-header of an additional frame.
3. A method as claimed in claim 1, wherein for each audio signal an
associated reference signal is included in a subheader of the first frame
which follows the additional frame and which contains information words of
the relevant audio signal in its data field.
4. A method as claimed in claim 1, characterized in that time information
is included in the data field of an additional frame.
5. An apparatus for recording a video signal and an associated audio signal
in the record carrier, comprising
a first input terminal for receiving the video signal,
a second input terminal for receiving at least two audio signals,
an encoding unit having a first input and a second input coupled to the
first input terminal and the second input terminal respectively, and
having an output terminal, which encoding unit is constructed to encode
the video signal and an audio signal to obtain the first information
signal and the second information signal respectively in the form of
successive information words, which is constructed to arrange the
information words in frames, which is constructed to insert a signal code
into a frame header to indicate the information signal to which the
information words in the data field of the associated frame belong, and
which is constructed to produce a sequence of frames on its output,
a recording unit, having an input coupled to the output of the encoding
unit, which recording unit is constructed to record the successive frames
in the record carrier, wherein the encoding unit is adapted to encode at
least a second audio signal associated with the video signal to form a
third information signal in the form of successive information words,
which is adapted to arrange said information words in frames, which is
adapted to insert a signal code into the frame header of frames containing
an encoded audio signal to indicate to which of the two or more audio
signals the information words in the data fields of these frames belong,
wherein the encoding unit comprises a reference-signal generator for
supplying reference signals, wherein the unit is further adapted to
generate additional frames, which additional frames contain said time
information pertaining to the time interval between the detection of a
reference signal and the instant a read-out video signal is to be
displayed for each of the two or more audio signals associated with a
video signal, and which is adapted to produce these additional frames on
its output terminal.
6. An apparatus as claimed in claim 5, wherein the encoding unit comprises
an audio encoding unit for encoding an audio signal, having an input
coupled to the second input terminal and having an output,
a video encoding unit for encoding a video signal, having an input coupled
to the first input terminal and having an output,
a signal-combination unit having a first input, a second input and a third
input coupled to the output of the audio encoding unit, the output of the
video encoding unit and the output of the reference-signal generator
respectively, and having an output coupled to the output terminal of said
apparatus, in that the encoding unit further has a third input termrnal
for receiving said time information, which third input terminal is coupled
to a fourth input of the signal-combination unit, and in that the
signal-combination unit is adapted to arrange the information words from
the audio-encoding unit and the video-encoding unit in the data fields of
frames, which is further adapted to insert the signal code into the frame
header of frames, and which is adapted to insert the time information into
the additional frames.
7. An apparatus as claimed in claim 6, wherein the signal-combination unit
is adapted to insert the reference signal into the sub-header of an
additional frame.
8. An apparatus as claimed in claim 6, wherein the signal-combination unit
is adapted to insert for each audio signal a reference signal associated
with the audio signal into the subheader of the first frame which follows
the additional frame and which contains information words of the relevant
audio signal in its data field.
9. An apparatus as claimed in claim 6, wherein the signal-combination unit
is adapted to insert the time information into the data field of an
additional frame.
10. An apparatus for reproducing a video signal and an associated audio
signal form a record carrier comprising
a read unit for reading successive frames of video signals and one of at
least two audio signals from the record carrier and for supplying said
frames to an output,
a decoding unit having an input coupled to the output of the read unit and
having a first output and a second output, which decoding unit is
constructed to separate frames containing information words of a first
information signal representing an encoded video signal and of frames
containing information words of a second information signal representing
encoded audio signals, which is constructed to decode the first
information signal and the second information signal to form the video
signal and the audio signal respectively, and which is constructed to
supply these signals to a first output terminal and a second output
terminal respectively, wherein the decoding unit has a control input for
receiving a first control signal and in that the decoding unit is adapted
to derive, under the influence of the first control signal signal, one of
the two or more audio signals and to supply this audio signal to its
second output terminal, in that the decoding unit is further adapted to
extract the reference signals and the additional frames from the
information read from the record carrier, to derive the time information
associated with the relevant audio signal under the influence of the first
control signal, said time information pertaining to the time interval
between the instant at which a reference signal is detected after read-out
and the instant at which a read-out video signal is to be displayed, to
derive the second control signal, and the supply a video signal to its
first output terminal under the influence of said second control signal.
11. An apparatus as claimed in claim 10, wherein the decoding unit
comprises a signal-separating unit, an audio decoding unit, a video
decoding unit, a control unit and a clock signal generator, in that the
input terminal is coupled to an input of the signal-separating unit, which
has a first output, a second output and a third output coupled to inputs
of the video-decoding unit, the audio-decoding unit and a first input of
the control unit respectively, wherein outputs of the video decoding unit
and the audio decoding unit are coupled to the first output terminal and
the second output terminal respectively, wherein an output of the
clock-signal generator is coupled to a second input of the control unit,
which has an output coupled to a control input of the video decoding unit,
and wherein the control input of the decoding unit is coupled to control
inputs of the signal-separating unit and the control unit, wherein the
signal-separating unit is adapted to extract the frames containing the
first information signal from the signal read from the record carrier and
to supply these frames to the first output, to extract frames containing
the relevant audio signal under the influence of the first control signal
applied to its control input and to supply these frames to its second
output, which is adapted to extract the reference signal and the
additional frames from the signal read from the record carrier, and to
supply these signals to its third output, wherein the control unit is
adapted to derive the time information associated with the relevant audio
signal from the additional frames under the influence of the first control
signal and is adapted to generate the second control signal on its output
from the time information derived and by means of the clock signal from
the clock signal generator, and wherein the video decoding unit is adapted
to decode the first information signal to form a video signal and is
adapted to supply this video signal to its output under the influence of
the second control signal.
12. An apparatus as claimed in claim 11 wherein the control unit is adapted
to extract the reference signal from the sub-header of an additional
frame.
13. An apparatus as claimed in claim 11 wherein the control unit is adapted
to extract the time information associated with the relevant audio signal
from a data field of an additional frame under the influence of the first
control signal. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The invention relates to a method of recording and/or reproducing a picture
signal and an associated audio signal in/from a record carrier, in which
during recording the picture signal and the audio signal are encoded to
form a first and a second information signal respectively comprising
information words arranged in frames, each frame comprising a frame header
and a data field, a data field of a frame comprising a plurality of
information words of the picture signal or an audio signal, the header
indicating the information signal to which the information words in the
data field belongs, after which the frames are recorded on the record
carrier; and in which during reproduction the frames are read from the
record carrier and are decoded to obtain the picture signal and the
associated audio signal. The invention also relates to an apparatus for
carrying out the method and to a record carrier obtained by means of the
method. A method of the type defined in the opening sentence is described
in the Applicant's previous Netherlands patent application No. 8,600,450.
More in particular, the invention relates to a method of recording and
reproducing picture signals and associated audio signals in the form of
digital information in/from a record carrier, such as for example, a
compact disc.
As is generally known, tne compact disc is a record carrier for the storage
of digital information, which record carrier can contain a specific number
of bits. The first application of the compact disc in the Compact Disc
Digital Audio System, which is already a few years old envisaged its use
as a record carrier for 16-bit PCM-encoded audio signals. For a
comprehensive description of this system reference is made to Philips'
Technical Review, Vol. 40, 1982, No. 6, in particular the article by J. P.
J. Heemskerk et al entitled "Compact disc system aspects and modulation,"
pages 157 to 164.
A second application envisaged its use as a data ROM for data-processing
equipment. A third application which is now being developed and envisages
its use as a record carrier for digitized video signals of pictures
accompanied by digital audio signals and, if desired, computer data.
The application of the compact disc now envisaged is an interactive use,
referred to as "CD-I". Papers on this novel use have already been read at
the Micro-soft Conference in Seattle, 3-5 Mar. 1986, namely a paper by D.
C. Geest entitled "Standardization of CD-I" and a paper by R. Bruno
entitled "New developments in optical media," which was published in the
"Philips Koerier" of Mar. 13, 1986, pages 1 and 2.
In order to enable a picture to be recorded on a record carrier of the
compact-disc type, the picture is divided into a plurality of lines (for
example 280 lines) and every line is divided into a plurality of
contiguous picture elements(for example 384 elements). It is assumed that
each picture element is of uniform brightness and uniform colour. A
picture element can be defined completely by a number of picture
components; namely the luminance component Y(i,k) and the two
colour-difference components U(i,k) and V(i,k) or, which is in principle
the same, by the three basic colour components R(i,k), G(i,k) and B(i,k).
Here i is the sequence number of the line and k the sequence number of the
picture element on this line (column).
Each of the picture components of a picture element is subjected to a
coding, so that for each picture element an information word is obtained,
hereinafter referred to as "video word". If PCM coding is applied the
picture components of each picture element are encoded separately, i.e.
independently of corresponding picture components of other picture
elements. However, if the picture components are subjected to a DPCM
coding, broadly speaking only the difference between the corresponding
picture components of every two successive picture elements is subjected
to a PCM coding. Since encoding such a difference generally requires a
smaller number of bits than separately encoding each of the picture
components, DPCM encoding is applied for each of the picture components in
the envisaged new application of the compact disc. This means that each
picture elexent is characterized by a 12-bit video word.
For a most economic use of the capacity of the record carrier the entire
block of 280.times.384 video words is transmitted only once. The monitor
comprises a picture memory having a number of storage locations which is
at least equal to the number of picture elements in the picture. Each
storage location is unambiguously associated with a picture element and
such a storage location contains the transmitted video word of the
relevant picture element. This picture memory is read out repeatedly in
the customary manner in order to display the relevant picture.
It is to be noted that in practice it is not found to be necessary to
transmit both the luminance component and the two colour-difference
components of each picture element. It is found to be satisfactory to
transmit the luminance contents of each picture element and alternately
the colour-difference component U and the colour-difference component V of
successive picture elements. This means that each picture element can be
characterized by an 8-bit video word. More in particular, the first four
bits of this video word represent the luminance component of the picture
element in DPCM format and the four other bits represent (alternately) one
of the two colour-difference components, also in DPCM format. Hereinafter,
the totality of video words to be transmitted, which together define a
specific picture, will be referred to as a "video block".
In the novel application of the compact disc now envisaged, a video block
is arranged in frames prior to recording on the record carrier, similarly
to the digitized information components, audio and computer data. Each
frame comprises, for example, 2352 bytes and each frame is roughly divided
into two fields, namely a frame header comprising 24 bytes and a data
field of 2328 bytes. The last 280 bytes in the data field may be used for
error protection and error correction of the other bytes in the data
field. This is utilized, for example, if the frame contains computer data.
The frame header inter alia comprises synchronization bytes for byte and
bit synchronization, but also indicates whether the data in the data field
is picture information, audio information or computer data. These cases
are referred to as a video frame, an audio frame and a computerdata frame
respectively. The data field of an audio frame comprises 1164 audio words
of 16 bits each, while the data field of a video frame comprises 2328
video words of 8 bits each.
The novel use of the compact disc now envisaged moreover provides the
possibility of choosing from a number of different audio-signal qualities.
Firstly, there is the quality known from the original use in the Compact
Disc Digital Audio system. This results in compact disc fully packed with
audio signals providing approximately 72 minutes of stereo sound of the
well-known compact-disc quality (a dynamic range of 90 dB or better).
Secondly, there is the "hifi music" mode. This possibility provides two
stereo channels which are reproducible parallel to each other or four mono
channels which are reproducible parallel to each other. A full compact
disc then provides approximately 72 minutes of sound per stereo channel.
Thus, if on a compact disc only one monosignal should be recorded, it is
possible to store 4.times.72 minutes of audio signal on a full compact
disc. The quality corresponds to that of a conventional long-play record.
Thirdly, there is the "midfi music" mode. In this case a full compact disc
contains four parallel channels, each channel accommodating a stereo
signal of 72 minutes length, or eight channels containing a mono signal of
72 minutes length. The quality corresponds to that of an FM radio
transmission.
A fourth possibility is the "speech" mode. This mode provides 8 parallel
channels of stereo or 16 parallel channels of mono signal of maximum 72
minutes length on a full compact disc. The quality is the same as that of
an AM radio transmission.
As is known, CD digital audio is encoded in accordance with a 16-bit PCM
code and the full storage capacity of the compact disc is necessary for
the storage bit of the 72-minute stereo signal.
The three other qualities with which the audio signal can be recorded on
the record carrier are realized by means of an 8-bit or 4-bit ADPCM code
(adaptive data pulse code modulation).
These three possibilities require a storage capacity of 50%, 25% and 12.5%
for the storage of the audio information of one channel. The remainder of
the storage capacity is then available for the storage of video
information, computer data or for other sound channels. In the
last-mentioned case it is possible to store speech in different languages
in a corresponding number of parallel channels.
A fifth possibility is to encode the speech phonetically, so that an even
longer playing time can be obtained. The standard phonetic alphabet as
specified for the desired lenguage or languages is encoded and recorded on
the compact disc together with a set of diphones for the desired language
and a resynthesis program by means of which the speech can be
resynthesized by joining the diphones to each other. The resulting
information density in one channel can be very high and may result in a
playing time of over 5000 hours for one full compact disc.
In those cases in which two or more parallel channels are available it is
possible, as stated previously, to store the same speech translated in
different languages in these channels on the compact disc. This is of
particular importance when simultaneously reproducing picture information
and associated speech, to provide a possibility of selecting the language
in which said speech is to be reproduced.
SUMMARY OF THE INVENTION
It is the object of the invention to provide steps eaabling picture
information together with one associated audio signal, selected from
different audio signals associated with the picture information, to be
reproduced from the record carrier. The audio signal is then for example a
text spoken in a certain language and associated with the picture
information (the picture). This picture information is associated with
other audio signals, i.e. the same text but spoken in another language
(other language). To this end the invention is characterized in that for
recording at least a second addio signal associated with the picture
signal the second audio signal is encoded to form a third information
signal comprising information words arranged in frames, in that the frame
headers of those frames which comprise an encoded audio signal moreover
indicates to which of the two or more audio signals the information words
in a data field of a frame belong, in that in addition reference signals
and additional frames are recorded on the record carrier, which additional
frames for each of the two or more audio signals associated with a picture
signal contain time information pertaining to the time interval between
the instant at which a reference signal is detected after read-out and the
instant at which a read-out picture signal is to be displayed on a picture
screen, and during reproduction the reference signals and the additional
frames are read from the record carrier, the time information associated
with one of the audio signals is derived from an additional frame under
the influence of a first control signal, and subsequently a second control
signal is derived from the time information thus derived and from a
detected reference signal for displaying a read-out picture signal on a
picture screen, and in that only said one audio signal is reproduced under
the influence of the first control signal.
The invention is based on the recognition of the fact that, one language
being of a more compact nature than the other language, or the successive
order of words in a sentence being different for a dfferent language, the
instant of displaying a picture associated with a text spoken in a
specific language need not be the same as in the case that said text
spoken in another language were reproduced. Therefore, for each language
the record carrier should contain information on the instants at which
successive pictures must be reproduced during a text spoken in a specific
language. This information is constituted by the time interval between the
instant at which a reference signal appears in the information read from
the record carrier and the instant at which a picture is displayed. Thus,
in general, this time interval will differ for the different audio signals
(languages). A reference signal may be inserted in, for example, the frame
header (for example the sub-header) of an addition frame. Another
possibility is to include an associated reference signal for each audio
signal (each language) in the frame header (for example, the sub-header)
of the first frame which follows the additional fram and which contains
information words of the relevant audio signal in a data field.
The time information may be included in the data field of an additional
frame. These additional frames are anyway preent on the record carrier and
contain the program to be read out add stored in the processor of the read
apparatus to ensure a correct operation of the apparatus.
The apparatus for recording a picture signal and an associated audio
signal, for carrying out the method, comprising
a first input terminal for receiving the picture signal,
a second input terminal for receiving the audio signal,
an encoding unit having a first input and a second input coupled to the
first input terminal and the second input terminal respectively, and
having an output terminal, which encoding unit is constructed to encode
the picture signal and the audio signal to obtain the first information
signal and the second information signal respectively in the form of
successive information words, which is constructed to arrange the
information words in frames, which is constructed to insert a signal code
into the frame header to indicate the information signal to which the
information words in the data field of the associated frame belong, and
which is constructed to produce a sequence of frames on its output,
a recording unit, having an input coupled to the output of the encoding
unit, which recording unit is constructed to record the successive frames
in the record carrier, is characterized in that the encoding unit is
adapted to encode at least a second audio signal associated with the
picture signal to form a third information signal in the form of
successive information words, which is adapted to arrange said information
words in frames, which is adapted to insert a signal code into the frame
header of frames containing an encoded audio signal to indicate to which
of the two or more audio signals the information words in the data fields
of these frames belong, in that the encoding unit comprises a
reference-signal generator for supplying reference signals, in that the
unit is further adapted to generate additional frames, which additional
frames contain said time information for each of the two or more audio
signals associated with a picture signal, and which is adapted to produce
these additional frames on its output terminal. Such an apparatus may be
characterized further in that the encoding unit comprises
an audio encoding unit for encoding an audio signal, having an input
coupled to the second input terminal and having an output,
a video encoding unit for encoding a picture signal, having an input
cuupled to the first input terminal and having an output,
a signal-combination unit having a first input, a second input and a third
input coupled to the output of the audio encoding unit, the output of the
video encoding unit and the output of the reference-signal generator
respectively, and having an output coupled to the output terminal, in that
the encoding unit further has a third input terminal for receiving said
time information, which third input terminal is coupled to a fourth input
of the signal-combination unit, and in that the signal-combination unit is
adapted to arrange the information words from the audio-encoding unit and
the video-encoding unit in the data fields of frames, which is further
adapted to insert the signal code into the frame header of frames, and
which is adapted to insert the time information into the additonal frames.
An apparatus for reproducing a picture signal and an associate audio
signal, for carrying out the method, comprising
a read unit for reading successive frames from the record carrier and for
supplying said frames to an outuut,
a decoding unit having an input coupled to the output of the read unit and
having a first output and a second output, which decoding unit is
constructed to separate frames containing information words of the first
information signal and of frames containing information words of the
second information signal, which is cnnstructed to decode the first
information signal and the second information signal to form the picture
signal and the audio signal respectively and which is constructed to
supply these signals to a first output terminal and a second output
terminal respectively, characterized in that the decoding unit has a
control input for receiving the first control signal and in that the
decoding unit is adapted to derive, under the influence of the first
control signal, one of the two or more audio signals and to supply this
audio signal to its second output terminal, in that the decoding unit is
further adapted to extract the reference signals and the additional frames
from the information read from the record carrier, to derive the time
information associated with the relevant audio signal under the influence
of the first control signal, to derive the second control signal, and to
supply the picture signal to its first output terminal under the influence
of said second control signal.
Such an apparatus may be characterized further in that the decoding unit
comprises a signal-separating unit, an audio decoding unit, a video
decoding unit, a control unit and a clock signal generator, in that the
input terminal is coupled to an input of the signal-separating unit, which
has a first output, a second output and a third output coupled to inputs
of the video-decoding unit, the audiodecoding unit and a first input of
the control unit respectively, in that outputs of the video decoding unit
and the audio decoding unit are coupled to the first output terminal and
the second output terminal respectively, in that an output of the
clock-signal generator is coupled to a second input of the control unit,
which has an output coupled to a control input of the video decoding unit,
and in that the control input of the decoding unit is coupled to control
inputs of the signal-separating unit and the control unit, in that the
signal-separating unit is adapted to extract the frames containing the
first information signal from the signal read from the record carrier and
to supply these frames to the first output, to extract frames containing
the relevant audio signal under the influence of the first control signal
applied to its control input and to supply these frames to its second
output, which is adapted to extract the reference signal and the
additional frames from the signal read from the record carrier, and to
supply these signals to its third output, in that the control unit is
adapted to derive the time information associated with the relevant audio
signal from the additional frames under the influence of the first control
signal and is adapted to generate the second control signal on its output
from the time information derived and by means of the clock signal from
the clock signal generator, and in that the video decoding unit is adapted
to decode the first information signal to form a picture signal and is
adapted to supply this picture signal to its output under the influence of
the second control signal.
DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described in more detail, by way
of example, with reference to the accompanying drawings. In the drawings
FIG. 1 represents a "slide show" with an associated text which may be
spoken in two languages,
FIG. 2 shows a record carrier,
FIG. 3 shows a number of successive frames in the information stream,
FIG. 4 shows the structure of a frame,
FIG. 5 represents the time information associated with the two languages,
FIG. 6 shows an apparatus for recording and
FIG. 7 shows an apparatus for reproducing pictures and associated speech.
DETAILED DESCRIPTION
FIG. 1 very schematically represents a "slide show" in which speech is
illustrated with pictures. In FIG. 1a the line e.sub.1 on the time axis t
very schematically represents an audio signal in the form of a text spoken
in a compact language, for example English. In FIG. 1b the line f.sub.1
very schematically represents the same text but now spoken in a more
ornate language, for example French. The text spoken in English is
shorter, from t=0 to t=t.sub.4e, than the text spoken in French. The
latter has a length from t=0 to t=t.sub.4f, where t.sub.4f >t.sub.4e, as
is apparent from FIG. 1.
The texts e.sub.1, f.sub.1 may comprise one sentence or a plurality of
sentences. A following text e.sub.2, f.sub.2 starts at the instants
t.sub.5e and t.sub.5f respectively. In order to ensure that the text
spoken in the two languages are nevertheless more or less synchronised
with each other, for example t.sub.5e is selected to be substantially
equal to t.sub.5f.
The texts e.sub.1 and f.sub.1 spoken in English and French respectively is
illustrated with three pictures B.sub.1, B.sub.2 and B.sub.3. As a result
of the differences in compactness or prolixity between the two languages
the pictures for the two languages should not be applied at the same
instants. From FIG. 1 it is evident that the pictures accompanied by the
English-language text will be applied at an earlier instant that when
accompanied by the French-language text, because t.sub.1e <t.sub.1f,
t.sub.2e <t.sub.2f and t.sub.3e <t.sub.3f.
When the picture signals of the three pictures and the two audio signals
corresponding to the English English and the French text are recorded in
the record carrier (compact disc) additional information has to be added
in order to ensure that during reproduction the pictures are applied at
the correct instants in conformity with the text spoken in one of the
languages.
FIG. 2 schematically represents the record carrier (compact disc). The
tracks extends over the record carrier 2 from the centre towards the
circumference along a spiral path and is also recorded and read from the
centre towards the circumference. The first spiral portion 3 between
points a and b is the lead-in area. This lead-in area contains inter alia
information on the contents of the record carrier. The portion 4 of the
track between points b and c contains frames of encoded audio signals,
frames of encoded picture signals, frames of computer data and additional
frames. These additional frames may be the same as the frames of computer
data. The spiral portion to the points c and d is the lead-out area. When
the read means (the leaser beam) reaches this lead-out area reproduction
and energization of the motor by means of which the record carrier is
rotated are terminated.
FIG. 3 schematically represents the contents of the track between the
points g and h in FIG. 2. The portion is selected in such a way that it
contains the (encoded) picture and audio information of the pictures and
the text of FIG. 1 spoken in English and the French language. The first
frame 6 in the portion between the points j and k in FIG. 2 is an
additional frame comprising a frame header 6.1 and a data field 6.2. The
frame header 6.1 is divided into a first part 6.h, also referred to as
"header", and a second part 6.5, is also referred to as "subheader". The
following frames 7,8 . . . . etc. are divided in the same way into a frame
header comprising a "header" and a "subheader", and a data field. FIG. 4
shows the structure of a frame in more detail. A frame, for example a
frame 8, comprises 2352 bytes in total and is divided into a frame header
8.1 comprising 24 bytes and a data field 8.2 comprising 2328 bytes.
Further, the frame header 8.1 is divided into a 12-byte synchronization
field S and a four byte first auxiliary field EH together forming the head
8.h and an p-byte second auxiliary field TH constituting the subheader.
The synchronization field S indicates the beginning of the frame. It
comprises one byte which only contains "0" bits followed by 10 bytes
consisting of "1" bits only and finally another byte consisting of "0"
bits only. The bytes in the first auxiliary field EH indicate the sequence
number of the frame in the track. The second auxiliary field TH indicates
whether the frame is a video frame, an audio frame or a computer-data
frame. It is to be noted that a compact disc contains approximately
324,000 (=72.times.60.times.75) frames in total. This is because a compact
disc can contain approximately 72 minutes of music, for which 75 frames
per second should be read.
The data field D is divided into data slots DS. For an audio frame these
data slots are selected in such a way that in each slot one 16-bit audio
word of a digital audio signal can be accommodated. For a video frame the
data slots are selected in such a way that each slot can contain one 8-bit
video word of a digital video signal. For computer-data frames these data
slots also have a length of one byte.
As already stated in the foregoing, each picture is divided into a matrix
of 280.times.384 picture elements A(i,k). Herein, i(=1, 2, . . . 280) is
the sequence number of the line (row) and k (=1, 2, . . . 384) is the
sequence number of the picture element on said line (column). If for each
picture element A(i,k) an eight-bit video word Q(i,k) is transmitted the
transmission of a complete picture requires approximately 47 video frames.
If a data field of a frame is filled with information words of an audio
signal recorded with the same quality as that of the Compact Disc Digital
Audio system, 75 audio frames contain information for approximately one
second of music. This is because, as stated previously, the record carrier
is read at a rate of 75 frames per second.
If an audio signal is recorded on the record carrier with a lower sound
quality after time compression an encoding, less audio frames are
necessary to obtain one second of music (audio signal) after reading,
decoding and time expansion. Thus, after reading an audio frame and after
conversion of the information in this audio frame into an audio signal it
may happen that an audio signal is reproduced during a long time interval
while a (video) picture should be displayed, for example, somewhere
halfway this time interval.
First of all, during recording on the record carrier allowance should be
therefore made for the fact that all the information necessary for a video
picture has already been read from the record carrier prior to the instant
at which a video picture should be displayed in the aforementioned time
interval during reading, and this information is available to be displayed
on a picture screen at the instant at which a control signal occurs.
Secondly, it is necessary to have information about the instant at which a
picture should be displayed within said time interval. It is not
sufficient to insert merely a control signal in the frame header of the
relevant audio frame withnn whose time interval (after time expansion of
the information read from the audio frame) a picture occurs. This is
because the picture should not be displayed at the instant at which this
control signal in the audio frame is read but at a later instant,
somewhere halfway said time interval.
Therefore, the record carrier should contain a control signal, hereinafter
referred to as the reference signal, and time information, the time
information indicating at which instant after a reference signal has been
detected during reading, a picture is to be displayed.
This time information may be inserted in one or more of the additional
frames. This means that for the various languages such an additional frame
contains a table listing the time intervals between the instant of
detection of the reference signal and the instant of displying a picture.
This table may be inserted in, for example, the data field of an
additional frame.
FIG. 5 shows such a table based on the example of FIG. 1. It is assumed
that during reading the reference signal for the two languages is detected
at the same instant, namely at the instant t=0 in the example of FIG. 1.
This is not necessarily so, as will become apparent hereinafter.
The reference signal may be inserted in, for example, the subheader of an
additonal frame. The reference signal is then detected after the relevant
additional frame has been read. Detection is now effected at the same time
for all languages.
Another possibility is to accommodate the reference signal in the subheader
of the first frame which follows the additional frame and whose data field
contains information words of the relevant language (the relevant audio
signal). This means that for each language an associated reference signal
is inserted in the subheader of the first frame which occurs after the
additional frame in the data stream and which contains information
pertaining to the relevant language. In this case detection for the
different languages is effected at different instants.
The reference signal may be inserted in a subheader, for example as a code
word having a specific configuration of "ones" and "zeros". After read-out
this code word (these code words) can be detected by means of a suitable
detector.
FIG. 6 shows an apparatus for recording a picture signal and an associated
audio signal. The apparatus comprises a first input terminal 11 for
receiving a picture (or video) signal, a second input terminal 12 for
receiving an audio signal, and a third input terminal 13 for receiving the
data. The apparatus comprises an encoding unit 23 comprising a number of
sections, namely: an audio encoding unit 14, a video encoding unit 15, a
data encoding unit 16 and a signal-combination unit 17.
The audio encoding unit 14 is adapted to encode at least two audio signals
(associated with the at least two languages) and to arrange these encoded
signals in frames. The audio encoding unit 14 comprises two encoding units
14' and 14" arranged in parallel. The audio signal corresponding to the
English-language text is applied to the sub-input 12' of the encoding unit
14' and is encoded in the encoding unit 14'. The audio signal
corresponding to the French-language text is applied to the sub-input 12"
of the encoding unit 14" and is encoded in the encoding unit 14". The
audio frames applied to the inputs 18 and 19 of the signal-combination
unit 17 by the encoding units 14' and 14" are arranged after each other by
the signal-combination unit and are serially applied to the output 20.
The encoding units 14' and 14" insert a signal code which indicates with
which of the two audio signals (corresponding to the English or French
text) the frames are associated into the subheader of each audio frame
which appear on their ouputs. This means that the encoding unit 14'
inserts one signal code corresponding to one audio signal (English) into
the sub-headers of all the frames supplied by the unit 14' and that the
encoding unit 14" inserts the other signal code corresponding to the other
audio signal (French) into the sub-headers of all the frames supplied by
the unit 14".
Instead of two parallel encoding units 14' and 14" the audio encoding unit
14 may comprise only one encoding unit. In that case there is only one
input terminal 12 instead of the sub-inputs 12' and 12". The audio signals
for the two languages should then be applied to the input terminal 12 in
time-multiplexed form. Obviously, the audio encoding unit 14 should then
be capable of separating the time-multiplexed signals, of encoding them
separately and of arranging them in frames. Further, the audio encoding
unit 14 should then be capable of inserting the correct one of the two
signal codes into the subheader of a frame. The audio encoding unit 14 now
combines the data frames to form a serial data stream which is applied to
the signal combination unit 17 via a signal line.
The video unit is constructed to encode the video signals applied to the
input terminal 11 and to arrange the encoded information in video frames,
which are subsequently applied to the signal combination unit 17 via the
input 21.
The data is applied to the data encoding unit 16 via the input terminal 13,
which unit encodes the data and arranges the data in data frames which are
applied to the input 22 of the signal combination unit 17.
The signal combination unit 17 joins the audio frames, the video frames and
the data frames in the correct sequence to each other. On the output 20
this yields a sequence of frames, for example as indicated in FIG. 3, the
frame 6 being, for example, a data frame. The frames 7 and 8 are, for
example, audio frames, the frame 7 being the audio signal corresponding to
(a part of) the English text of FIG. 1 and the frame 8 being the audio
signal corresponding to (a part of) the French text of FIG. 1. The frame 9
may be, for example, a video frame. The data applied via the input
terminal 13, which data is encoded and arranged in data frames by the
encoding unit 16, inter alia contains the afore-mentioned time information
(see FIG. 5). Thus, the time information is also encoded by the encoding
unit 16 and accommodated in one or more data frames. Suitably, tee time
information is inserted in the data field of a data frame, i.e. for
example in the data field 6.2 of the data frame 6.
The apparatus shown in FIG. 6 comprises a reference-signal generator 25
which receives a control signal via a control input 27 and, d | | |
