Re: [FFmpeg-devel] [PATCH 02/18] fftools/ffmpeg_filter: refactor setting input timebase

From: "Martin Storsjö" <martin@martin.st>
To: FFmpeg development discussions and patches
	<ffmpeg-devel@ffmpeg.org>,
	 FFmpeg development discussions and patches
	<ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 02/18] fftools/ffmpeg_filter: refactor setting input timebase
Date: Mon, 11 Mar 2024 14:29:15 +0200 (EET)
Message-ID: <9a7a9c5f-f377-bca8-26e1-6bfe12589ed2@martin.st> (raw)
In-Reply-To: <171015983262.662.304106510805949905@lain.khirnov.net>

On Mon, 11 Mar 2024, Anton Khirnov wrote:

> Quoting Tobias Rapp (2024-03-11 11:12:38)
>> On 10/03/2024 23:49, Anton Khirnov wrote:
>>
>>> Quoting James Almer (2024-03-10 23:29:27)
>>>> On 3/10/2024 7:24 PM, Anton Khirnov wrote:
>>>>> Quoting Michael Niedermayer (2024-03-10 20:21:47)
>>>>>> On Sun, Mar 10, 2024 at 07:13:18AM +0100, Anton Khirnov wrote:
>>>>>>> Quoting Michael Niedermayer (2024-03-10 04:36:29)
>>>>>>>> why not automatically choose a supported timebase ?
>>>>>>>> "[mpeg4 @ 0x55973c869f00] timebase 1/1000000 not supported by MPEG 4 standard, the maximum admitted value for the timebase denominator is 65535"
>>>>>>> Because I don't want ffmpeg CLI to have codec-specific code for a codec
>>>>>>> that's been obsolete for 15+ years. One could also potentially do it
>>>>>>> inside the encoder itself, but it is nontrivial since the computations
>>>>>>> are spread across a number of places in mpeg4videoenc.c and
>>>>>>> mpegvideo_enc.c. And again, it seems like a waste of time - there is no
>>>>>>> reason to encode mpeg4 today.
>>>>>> This is not mpeg4 specific, its just a new additional case that fails
>>>>> The case you reported is mpeg4 specific.
>>>>>
>>>>>> ./ffmpeg -i mm-small.mpg test.dv
>>>>>> [dvvideo @ 0x7f868800f100] Found no DV profile for 80x60 yuv420p video. Valid DV profiles are:
>>>>> There is no mechanism for an encoder to export supported time bases.
>>>> Could it be added as an extension to AVProfile, or AVCodec?
>>> The two cases are actually pretty different:
>>> * mpeg4 has a constraint on the range of timebases, and actually does
>>>    some perverted computations with the timestamps
>>> * DV just needs your video to be CFR, with a list of supported
>>>    framerates; dvenc should probably read AVCodecContext.framerate
>>>    instead of time_base
>>>
>>> But most importantly, is there an actual current use case for either of
>>> those encoders? They have both been obsolete for close to two decades.
>>> It seems silly to add new API that won't actually be useful to anyone.
>>
>> Hardware doesn't get outdated as quickly as software. And there are
>> people that do not switch their full environment to a new codec every
>> decade just to be "in line".
>
> And your point is...?

I think the point is, that one can't just dismiss that anybody would want 
to encode mpeg4 video any longer, even if it is obsolete. I also would 
like to keep being able to do that.

That said, I haven't followed the discussion closely enough about what to 
do with the time bases.

// Martin

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