Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
2000-11-15
2004-10-26
Boccio, Vincent (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C386S349000, C386S349000, C386S349000
Reexamination Certificate
active
06810198
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a record and playback device, such as a digital VCR, for recording or playing back data including a video signal and an audio signal.
BACKGROUND OF THE INVENTION
Recently an innovative broadcasting method is developed such as a high definition television (HDTV), and in the U.S., a digital television (DTV) method has been commercialized.
In the DTV broadcasting system, a video signal is coded through Moving Picture Experts Group—2 (MPEG 2) method and is combined with a multi-channel audio signal, e.g. by a Dolby Digital method, then is broadcast as a digital broadcasting. Meanwhile, MPEG 2 is disclosed as 13818 standard of International Organization for Standardization/International Electro-technical Commission (ISO/IEC). The digital broadcasting features that multi-channels can be transmitted with quality picture in a narrow frequency bandwidth because video signals are compressed and coded.
In this climate, portable devices and studio devices capable of the HDTV method have been developed. However, those devices are expensive and thus producing the program for the HDTV broadcasting incurs a lot of cost and time. Accordingly the program is sometimes produced by converting a cinema film to TV application. In the U.S., film oriented programs are usually on-aired through the DTV.
Cinema-film has typically has 24 frames per second, i.e. it produces a progressive scanning signal of 24 Hz frame frequency (hereinafter referred to as a
24
p
signal). On the other hand, a VCR handles a TV signal of 30 Hz frame frequency. Therefore, conversion of the frame frequency is necessary. Converting a cinema film into TV signals is generally called telecine conversion. This conversion is known as 2:3pull down technique.
When the converted signal through 2:3pull down technique is recorded in a conventional VCR, the same field is repeated, which limits an edit process. Therefore, it is desired that the cinema film as it is, i.e. at a frame frequency of 24 Hz, to be recorded with the VCR.
In audio devices, DVD-AUDIO standard is established for digital Versatile Disc (DVD). According to this standard, an audio signal sampled at 96 kHz is recorded and played back, and sound of the higher quality than that of a conventional method is obtainable. As such, due to an introduction of a digital technique, an audio signal of higher quality is going to be available at home.
An instance of the VCR that records and plays back the HDTV signal is HD-D5·VCR. A video signal is coded complying with HD-D5 method which is disclosed in 342M standard of Society of Motion Picture and Television Engineers (SMPTE). The HD-D5·VCR is disclosed in SMPTE 279M standard.
The HD-D5·VCR records and plays back a video signal of interlace scanning and an audio signal of four channels. Details of respective signals are as follows:
video signal; a number of scanning lines=1125 lines, a number of active scanning lines=1080 lines, field frequency=60 Hz (or 59.94 Hz)
audio signal; sampling frequency=48 kHz, a number of quantizing bits=20.
When a video signal of 24 Hz frame frequency is recorded with the VCR discussed above, an equivalent frequency for overall signal process is lowered by 24 /30 for record and playback comparing with the case where a video signal of 30 Hz frame frequency (60 Hz field frequency) is recorded.
Data amount per frame of the video signal remains the same regardless of 24 Hz or 30 Hz frame frequency, therefore, changing the rotational components from 24 Hz system to 30 Hz system allows video data to be recorded in the same tape format.
On the other hand, as for the audio signal, input data corresponding to one field of the video signal are collected in every input channel, and an error correcting code is added before the audio signal is recorded.
In the case of recording a video signal of 30 Hz frame frequency, a number of audio samples per one channel, one field of a digital audio signal sampled at 48 kHz is 48000/60=800. In the case of 24 Hz frame frequency, it is 48000/48=1000. As such, the numbers of samples per field are different between 24 Hz and 30 Hz, the audio signal thus cannot be recorded in the same recording area.
Then an audio sampling frequency is converted to 48000×24/30=38400 Hz by using a digital filter. A number of samples of the audio signal of which sample frequency is converted to 38.4 kHz is 38400/48=800 per one channel and one field, this is the same value as the case where a frame frequency is 30 Hz. Thus this audio signal can be recorded in the same recording area on tape.
However, the method discussed above uses the digital filter for converting the audio sampling frequency, and this deteriorates sound quality depending on a number of taps or bits. Further, this lowers the sampling frequency, and if the original frequency bandwidth is not limited to a certain extent, return distortion would occur. Therefore, the frequency bandwidth of the input audio signal should be limited.
The conventional method discussed above records and plays back only an audio signal of four channels. When a program material for the HDTV is made from a cinema film, an original cinema film contains audio signals in multi-channel form typically represented by Dolby Digital method. The Dolby Digital method uses the data of six channels while a VCR which records and plays back the cinema film only uses four channels for audio signals. For recording the audio signal of the cinema film as they are, the VCR which can uses at least six channels or preferably eight channels is demanded.
The conventional method discussed above records and plays back only the audio signal sampled at 48 kHz, and cannot record and play back a higher quality sound such as the audio signal sampled at 96 kHz or the audio signal quantized with 24 bits.
In general, two methods are available to increase a number of audio channels.
The first method is to compress the audio data more than four channels to the data of four channels, and record the compressed data with the conventional VCR. However, when the data is compressed, sound quality is somewhat lowered, therefore, this method cannot be accepted as a VCR for producing a source program. Further, the compression produces some delay, and this causes the entire system to be complicated. The compression further amplifies the influence due to an error produced in the VCR.
The second method is to develop a totally new tape format complying with the multi-channel audio signals. Developing the new tape format allows arbitrary design of devices; however, it takes a lot of time and costs a lot of money for developing the devices, and it is difficult for a new device to be compatible with the conventional format.
For usability of the VCR, it is desirable that a conventional record/playback device—which handles audio data of only four channels—plays back a recorded medium, in which audio data of more than four channels are recorded, to reproduce the sound of four channels (downward compatibility). It is also desirable that a recorded medium—which was recorded with the conventional record/playback device—is played back with a record/playback device, capable of handling more than four channels, to reproduce sound of four channels (upward compatibility).
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above.
A record/playback device of the present invention complies with a first format in which a first video signal and a first audio signal are to be recorded, and a second format in which a second video signal and a second audio signal are to be recorded. The second video signal has a lower frame frequency than the first video signal and the second audio signal has the same data amount per unit time as the first audio signal. The record/playback device comprises the following elements:
(a) a video processor for outputting video recorded data having the same frame frequency as an input video signal, where the input video signal is the first or the seco
Bannai Tatsushi
Kato Shiro
Kuroda Tokuji
Boccio Vincent
Fletcher James A.
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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