Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1999-10-14
2003-01-28
Boccio, Vincent (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C348S423100, C348S515000, C375S240260, C375S240280
Reexamination Certificate
active
06512884
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for synchronized play back of audio-video signals, which have a high performance when particularly plural digitally compressed audio data and digitally compressed video data are decoded and played back.
DESCRIPTION OF THE RELATED ART
Generally, an apparatus for synchronized play back of audio-video signals reads digitally compressed audio-video (AV) signals recorded in a recording medium. such as a CD-ROM or a hard disk (HD) and plays back on a CRT monitor and to a speaker by decompressing the signals.
However, at a conventional apparatus for synchronized play back of audio-video signals, the performance of a clock is not sufficient, consequently, there is a problem that sufficient resolution applying for synchronizing control can not be obtained. In order to solve this problem, Japanese Patent Application Laid-Open No. HEI 10-136308 discloses an apparatus for synchronized play back of audio-video signals.
In this application, reference time is obtained from the amount of data of played back audio data (for example, pulse code modulation (PCM) data), and video playing back is made to synchronize with this reference time (for example, by frame dropping of video data), and synchronized play back of audio-video signals is performed.
In this apparatus, as mentioned in this application, audio signals can be processed as the first priority, consequently the audio data do not become intermittent. Therefore, the play back without abnormal feeling can be performed, and when frame dropping is performed, the frame dropping is performed in the order of the frame whose priority is high, as a result, video signals can be smoothly played back.
However, at conventional apparatuses for synchronized play back of audio-video signals, a case that plural compressed audio data are multiplexed is not considered. For example, at the conventional technology of the mentioned above application, at the play back of the compressed AV data whose plural audio data are multiplexed, there is a case that audio data are changed over. In this case, when the compressed multiplexing AV data to be separated are merely changed over, generally, the AV separation from the compressed AV data is sequentially performed. However there is a problem that the compressed audio data applied the AV separation, which should be essentially played back at the same time at before and after the changing over, are overlapped, or the separated compressed audio data to be played back at designated time are lost.
FIGS. 1 and 2
are conceptual diagrams showing a series of compressed multiplexing AV data and a series of compressed audio data applied AV separation, at the conventional apparatus for synchronized play back of audio-video signals. Referring to
FIGS. 1 and 2
, the problem mentioned above is explained in detail. In
FIGS. 1 and 2
, in Audio N
T
, N means the number of audio and
T
means time.
For example, in
FIG. 1
, when the compressed multiplexing AV data are changed over from audio (
0
) to (
1
) at point A, at the separated compressed audio data, the audio data at time (
0
) and (
1
) are overlapped. In
FIG. 2
, when the compressed multiplexing AV data are changed over from audio (
1
) to (
0
) at point B, at the separated compressed audio data, the audio data at time (
2
) and (
3
) are lost.
As mentioned above, at the conventional apparatus in which reference time is obtained from the amount of cumulative data (for example, PCM data) outputted from the starting of play back, the reference time after the audio data are changed over has time lag or lead, and the synchronized play back after the audio data are changed over is not secured.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and an apparatus for synchronized play back of audio-video signals in which time lag or lead of the reference time after the audio data are changed over can be avoided and the performance of the synchronized play back after the audio data are changed over can be increased, even in a case that plural digitally compressed audio data are separated and played back.
According to a first aspect of the present invention, for achieving the objects mentioned above, a method for synchronized play back of audio-video signals, which decodes and plays back plural digitally compressed audio data and digitally compressed video data, when said plural digitally compressed audio data are changed over and one of said plural digitally compressed audio data is selected and played back, provides the steps of obtaining reference time based on the amount of played back data of said changed over decoded audio data, and playing back said changed over decoded audio data synchronizing with video data decoded said digitally compressed video data, based on said reference time.
According to a second aspect of the present invention, in the first aspect, said reference time T based on the amount of played back data of said changed over decoded audio data is calculated by an equation, T=T
2
+T
1
−T
3
, using the following T
1
, T
2
and T
3
, decoding start time T
1
for said changed over audio data to be decoded, played back time T
2
of decoded audio data calculated by the amount of the played back data of said changed over decoded audio data, and decoding start time T
3
for said video data to be decoded.
According to a third aspect of the present invention, in the first aspect, when said changed over decoded audio data are played back synchronizing with said video data decoded digitally compressed video data, based on said reference time, the present invention further provides the step of comparing time that said reference time T is added to said decoding start time T
3
for said video data to be decoded with decoding time of the oldest inputted frame to be decoded in frames of undecoded video data in said digitally compressed video data. When said added time is prior time to said decoding time of said oldest inputted frame to be decoded, by judging a preceding state whose preceding time is time from said added time to said decoding time of said oldest inputted frame, the present invention provides the step of weighting for decoding for said video data corresponding to said preceding time. And when said added time is posterior time to said decoding time of said oldest inputted frame to be decoded, by judging a delaying state whose delaying time is time from said decoding time of the oldest inputted frame to said added time, the present invention provides the step of frame dropping of number of frames corresponding to said delaying time for said video data.
According to a fourth aspect of the present invention, in the third aspect, said frame dropping of the number of frames corresponding to said delaying time for said video data makes frames to be dropped give the order of priority and performs the frame dropping from the frames having high priority.
According to a fifth aspect of the present invention, an apparatus for synchronized play back of audio-video signals provides an audio-video (AV) separating means, to which compressed multiplexing data of digitally compressed video data and plural digitally compressed audio data are inputted, and separates the inputted data into the digitally compressed video data and instructed audio data corresponding to an index (ID) instructed from an external input through an audio changing over means in said plural digitally compressed audio data, a video decoder, in which said digitally compressed video data separated at said AV separating means are decoded, and outputs the decoded video data, an audio decoder, in which said instructed audio data separated at said AV separating means are decoded, and outputs the decoded audio data, an audio play back controlling means in which playing back of said decoded audio data is controlled, an audio counter which calculates the amount of played back data of said decoded audio data played back at said audio play back controlling means, a cloc
Boccio Vincent
Foley & Lardner
NEC Corporation
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