[vlc-devel] [RFC PATCH 3.0.x] input: clear EOF flags of slave sources when select track

[Zhao Zhili]

> On Nov 14, 2020, at 2:46 AM, Rémi Denis-Courmont <remi at remlab.net> wrote:
> 
> Le vendredi 13 novembre 2020, 16:06:37 EET Zhao Zhili a écrit :
>> input-slave was broken for some demuxers like mp4. If no track is
>> selected, slave demuxer return EOF at the beginning. Selecting
>> a track of slave input doesn't work since the input source is
>> in the EOF status. For VLC users, seeking after select track is a
>> workaround solution, because seek will reset the EOF flag.
>> 
>> Since a video track can be enabled at random position and there is
>> no preroll, it can lead to corrupted frames.
> 
> I don't think you can simply undo the EOS flag. AFAIK, demuxers are not 
> *generally* robust enough to return EOS repeatedly.
> 
> Most likely some demuxers return a fatal error or even crash if you try to 
> demux after EOS (without first seeking). We can agree that that's a bug in any 
> affected demuxers ... in 4.0. But we can't just decree a change in the API 
> semantics, without first reviewing the demuxers.

There are two other methods:
1. Trigger SlaveSeek() when selecting track.

2. Output all tracks from demuxers and let EsOut drop those unselected track packets.
Actually, --demux=avformat is another workaround.

How about the first method for 3.0?

> 
> It's unlikely that we can do this in a stable release at all.
> 
> -- 
> Rémi Denis-Courmont
> 
> 
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