[vlc-devel] [PATCH] demux: mkv: fix seek

[Zhao Zhili]

> On Jun 29, 2018, at 10:36 PM, Steve Lhomme <robux4 at ycbcr.xyz> wrote:
> 
> Hi
> 
> 
> On 2018-06-26 11:48, Zhao Zhili wrote:
>> This fixes a regression from 6b10c2e6. Seek failed due to empty
>> _tracks_seekpoints[video_track].
>> ---
>>  modules/demux/mkv/matroska_segment.cpp | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>> 
>> diff --git a/modules/demux/mkv/matroska_segment.cpp b/modules/demux/mkv/matroska_segment.cpp
>> index 148e66e..844558c 100644
>> --- a/modules/demux/mkv/matroska_segment.cpp
>> +++ b/modules/demux/mkv/matroska_segment.cpp
>> @@ -635,6 +635,15 @@ bool matroska_segment_c::Preload( )
>>                  cluster = kc_ptr;
>> +
>> +            // add first cluster as trusted seekpoint for all tracks
> 
> Not exactly trusted, it just kickstarts the seeking with a known position.
> 
>> +            for( tracks_map_t::const_iterator it = tracks.begin();
>> +                 it != tracks.end(); ++it )
>> +            {
>> +                _seeker.add_seekpoint( it->first,
>> +                    SegmentSeeker::Seekpoint( cluster->GetElementPosition(), 0 ) );
> 
> It marks the Seekpoint as TRUSTED, ie sure to be a seek point for that track because we encountered a keyframe. Thie may not be the case at all.
> SegmentSeeker::Seekpoint::TrustLevel::QUESTIONABLE would be better here.

Good point.

> 
> Also a pts of 0 may not be correct. A Segment can start with a high PTS if it's the continuation of a previous Segment. So using -1 here is better (technically it should be VLC_TS_INVALID but that's not what the code expects).

Yes, -1 is better. Technically it should be VLC_TS_LOWER_BOUND but we don't have that. INVALID doesn't mean it's small, although let VLC_TS_INVALID equal to INT64_MAX will break a lot of code I guess.

> 
> After these 2 changes the fix still works but it's cleaner.
> 
>> +            }
>> +
>>              /* stop pre-parsing the stream */
>>              break;
>>          }
>> -- 
>> 2.9.5
>> 
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