Re: [FFmpeg-devel] [PATCH v3 2/2] avcodec: add external dec libvvdec for H266/VVC - Cosmin Stejerean via ffmpeg-devel

From: Cosmin Stejerean via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: "FFmpeg development discussions and patches" <ffmpeg-devel@ffmpeg.org>
Cc: "Cosmin Stejerean" <cosmin@cosmin.at>
Subject: Re: [FFmpeg-devel] [PATCH v3 2/2] avcodec: add external dec libvvdec for H266/VVC
Date: Mon, 20 May 2024 18:39:18 +0000
Message-ID: <0101018f974d049f-8790f032-e8d1-421f-95bd-e466334fb435-000000@us-west-2.amazonses.com> (raw)
In-Reply-To: <14303208.qZsRhMg2gi@basile.remlab.net>

> On May 20, 2024, at 11:03 AM, Rémi Denis-Courmont <remi@remlab.net> wrote:
> 
> Le maanantaina 20. toukokuuta 2024, 19.33.43 EEST Cosmin Stejerean via ffmpeg-
> devel a écrit :
> 
>> hwaccel decoding seems somewhat orthogonal
> 
> How exactly will that work then? Either vvdec is the default, and hwaccel 
> won't work, or vvdec is not the default and it's essentially dead code.

The same way using FDK-AAC as a decoder works, if you want to use it as the *AAC decoder you have to specify the decoder with -c:a libfdk_aac before the input.-

> 
>>> Providing a non-default choice is a poor excuse for a bug. Most users
>>> won't know how to do that, and many FFmpeg reverse dependencies don't
>>> even allow it.
>> 
>> Need better documentation then?
> 
> Well, good luck with that. Documentation for working around as yet unknown 
> bugs sounds a bit difficult to write, and even then, requiring manual decoder 
> selection seems very user-hostile to me.

Where is the "requiring" part coming in? I'm saying that manual decoder selection is an option in the ffmpeg CLI, and can be used to select an alternate decoder if the default one is not sufficient for some reason. 

This is a thing I've had to do repeatedly over the past few years for FDK-AAC.

> 
>> Not sure that designing for the lowest common denominator of reverse
>> dependencies is the best way to do things, but at a minimum one can rebuild
>> ffmpeg with only one decoder enabled to get around this.
> 
> To the contrary, gstreamer, mpv, VLC et al. are better equipped to handle 
> this, starting with a proper plugin architecture.

Better equipped to handle what? For the usecase of transcoding it doesn't matter whether or not downstream player dependencies do or don't expose alternate decoders in libavcodec, to the extent they even use libavcodec for decoding.

So it seems weird to reject a patch to add a decoder option because it may or may not be useful to the downstream players.

- Cosmin
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