Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Patent
1996-10-10
2000-09-05
Tran, Thai
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
386 81, 386111, H04N 5783
Patent
active
061155322
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the field of digital video recording, and in particular to reproduction of an high definition video signal at a non-standard speed.
BACKGROUND OF THE INVENTION
A digital video cassette recorder employing a helical scanning format has been proposed by a standardization committee. The proposed standard specifies digital recording of either standard definition (SD) television signals, for example NTSC or PAL, and high definition television signals having an MPEG compatible structure, such as a proposed Grand Alliance signal. The SD recorder utilizes a compressed component video signal format employing intra field/frame DCT with adaptive quantization and variable length coding. The SD track format comprises 10 .mu.m tracks, azimuth recorded without guard bands, with 10 or 12 tracks per NTSC or PAL frame respectively. The tape cassette employs 1/4" wide tape with an evaporated metal recording medium. The SD digital VCR or DVCR, is intended for consumer use and has sufficient data recording capability to record either NTSC (PAL) signals, or an advanced television signal.
An advanced television or ATV signal has been developed by the Grand Alliance (GA) consortium. A specification document titled Grand Alliance HDTV System Specification was published in the 1994 Proceeding of the 48.sup.th Annual Broadcast Engineering Conference Proceedings. The GA signal employs an MPEG compatible coding method which utilizes an intra-frame coded picture, termed I frame, a forward predicted frame, termed a P frame and a bidirectionally predicted frame, termed a B frame. These three types of frames occur in a group known as a GOP or Group Of Pictures. The number of frames in a GOP is user definable but may comprise, for example, 15 frames. Each GOP contains one I frame, which is abutted by B frames, which are then interleaved with P frames.
In an analog consumer VCR, "Trick Play" or TP features such as picture in forward or reverse shuttle, fast or slow motion, are readily achievable, since each recorded track typically contains one field. Hence reproduction at speeds other than standard, result in the reproducing head, or heads, crossing multiple tracks, and recovering recognizable horizontal picture segments. The GOP of an ATV signal, employing I, P and B frames, may be recorded occupying multiple tracks on tape, for example, 10 tracks per frame and 150 tracks per GOP. Simply stated, when a DVCR is operated at a non-standard reproduction speed, replay heads transduce sections or segments from multiple tracks. Unfortunately these track segments no longer represent sections from discrete records of consecutive image fields. Instead, the segments contain data resulting mainly from predicted frames of the GOP. During play speed operation, I frame data is recovered which permits the reconstruction of the predicted B and P frames. Clearly, during "Trick Play" operation, the amount of I frame data recovered progressively diminishes as TP speed increases. Hence, the possibility of reconstructing B and P frames from the reproduced pieces of I frame data is virtually zero. Thus, the provision of "Trick Play" or non-standard speed replay features requires that specific data be recorded, which when reproduced in a TP mode, is capable of image reconstruction without the use of adjacent frame information. Furthermore, since "Trick Play" specific data is recorded, the physical track location must be such to permit recovery in a TP mode.
SUMMARY OF THE INVENTION
In accordance with an inventive arrangement a digital video recorder for reproducing digital image signals at different reproducing speeds, said recorder comprises: a transducer for recovering a digital signal from a recorded medium, the digital signal having a first data signal representing the digital image signals and a second data signal representing a processed form of the digital image signals; means coupled to the transducer for separating the digital signal into the first and the second data signals; means responsive to a selection of one of the
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Davenport Francis A.
Laks Joseph J.
Thomson Licensing S.A.
Tran Thai
Tripoli Joseph S.
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