[Mp4-tech] Timing question

[Gary Sullivan]

"Ram" et al,
It is not really true that "time resolution" is fixed to 30000 in H.263.   The standard uses a term called the "picture clock frequency".  The default PCF is 30000/1001.  It is also possible to us a "custom PCF". A custom PCF is given by 1 800 000 / (clock divisor * clock conversion factor), where clock divisor can have values of 1 through 127 and clock conversion factor can either be 1000 or 1001.  There was a very old version of the standard that did not support custom PCF, but that capability was added about 10 years ago.
Also, PAL does not use 29.97 fps.  It is 25 fps.  NTSC is 30000/1001 fps (which is approximately, but not exactly, equal to 29.97 fps).
Best Regards,
Gary Sullivan
________________________________
From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Ram
Sent: Wednesday, January 23, 2024 7:30 AM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] Timing question
Hi Guys,
I primarily work with H263 and MPEG4 video codecs. In all video codecs thers is this parameters in the stream called Time resolution. In H263 they say it's fixed to 30000
so that they can achieve 29.97 fps which equals line frequencies used in PAL.
What is the best value to choose when someone transcodes between H263 and MPEG4 in either direction.
'Thanks,
Ram
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