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

[Zhao Zhili]

> On Nov 16, 2020, at 10:59 PM, Rémi Denis-Courmont <remi at remlab.net> wrote:
> 
> Le lundi 16 novembre 2020, 14:03:54 EET Thomas Guillem a écrit :
>> On Sat, Nov 14, 2020, at 07:48, Zhao Zhili wrote:
>>>> 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.
>> 
>> If the seek is done only on the EOF slave, then such workaround is OK for
>> me.
> 
> I don't think that would work. In fact, seeking is problematic as it is - 
> because different sources may have different precision.
> 
> But in this case, we *must* seek the demuxer that returned EOF. And IMU, 
> that's the maine one.

OK I got it. Seek the main demuxer so slave demuxers will follow it. 

> 
> -- 
> Rémi Denis-Courmont
> 
> 
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