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A disc has one track (stream) of MPEG-2 constant bit rate (CBR) or variable bit rate (VBR) compressed digital video. A restricted version of MPEG-2 Main Profile at Main Level (MP@ML) is used. SP@ML is also supported. MPEG-1 CBR and VBR video is also allowed. 525/60 (NTSC, 29.97 interlaced frames/sec) and 625/50 (PAL, 25 interlaced frames/sec) video display systems are expressly supported. Coded frame rates of 24 fps progressive from film, 25 fps interlaced from PAL video, and 29.97 fps interlaced from NTSC video are typical. MPEG-2 progressive_sequence is not allowed, but interlaced sequences can contain progressive pictures and progressive macroblocks. In the case of 24 fps source, the encoder embeds MPEG-2 repeat_first_field flags into the video stream to make the decoder either perform 2-3 pulldown for 60Hz (59.94) displays or 2-2 pulldown (with resulting 4% speedup) for 50Hz displays. In other words, the player doesn't really "know" what the encoded rate is, it simply follows the MPEG-2 encoder's instructions to produce the predetermined display rate of 25 fps or 29.97 fps. (Very few players convert from PAL to NTSC or NTSC to PAL. See 1.19.)
It's interesting to note that even interlaced source video is often encoded as progressive-structured MPEG pictures, with interlaced field-encoded macroblocks used only when needed for motion. A computer can mostly ignore the repeat_first_field flags and re-interleave (weave) the video fields back into full-resolution progressive frames, which works especially well at 72 Hz refresh rate (3x24). Computers can improve the quality of interlaced source by doubling the lines in fields (bobbing) and displaying them as progressive frames at twice the normal rate. Most film source is encoded progressive (the inverse telecine process in the encoder removes duplicate 2-3 pulldown fields from videotape source); most video sources are encoded interlaced. These may be mixed on the same disc, such as an interlaced logo followed by a progressive movie.
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кто юзал DVD Player JVC 721 -- Alexsei -- 15.03.01@18:46 (Чит.: 94)