[Mp4-tech] Timing question

[Nicolas El Hani]

Hello Everyone, 
It's my first time on the mailing list, so excuse me if I'm emailing the wrong address or something is wrong in my etiquette, just let me know! I'm currently starting a business that involves video production. I have a basic fundamental question that maybe is not a very smart question, but basically is there inherently an advantage to encode a video in the "main" profile of h.264 over the "baseline" profile. I know the complexity of the main encoding is higher. So basically if you had the same file encoded in baseline and another one in main, with similar data rates (say 1500kbps) would the end result be the same? I'm going to be encoding video mostly in VGA resolution and start to drift towards 720p. The reason I ask is because final delivery to clients would be much better if the file could be viewed both on mobile devices (iphone, ipod, nokias, etc...) and locally on a computer or TV. But if encoding in baseline at the same resolution will compromise quality because of its macroblocks or algorithms at the encoding stage than it's worth it to use just main and if need be for mobile viewing deliver a second file in baseline. But it would really be much simpler and would streamline the business if baseline could hold up to the main. Thank you so much and I hope it's  not too much of a bother! Cheers.
Nick
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> From: garysull windows.microsoft.com
> To: rramani gmail.com; mp4-tech lists.mpegif.org
> Date: Wed, 23 Jan 2024 11:03:02 -0800
> Subject: RE: [Mp4-tech] Timing question
> CC:
> 
> "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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