On 10/04/2017 03:21 PM, Michael Niedermayer wrote: > On Wed, Oct 04, 2017 at 10:58:19AM -0700, John Stebbins wrote: >> On 10/04/2017 10:13 AM, Michael Niedermayer wrote: >>> On Wed, Oct 04, 2017 at 08:18:59AM -0700, John Stebbins wrote: >>>> On 10/04/2017 03:50 AM, Michael Niedermayer wrote: >>>>> On Fri, Sep 29, 2017 at 08:54:08AM -0700, John Stebbins wrote: >>>>>> When keyframe intervals of dash segments are not perfectly aligned, >>>>>> fragments in the stream can overlap in time. Append new "trun" index >>>>>> entries to the end of the index instead of sorting by timestamp. >>>>>> Sorting by timestamp causes packets to be read out of decode order and >>>>>> results in decode errors. >>>>>> --- >>>>>> libavformat/mov.c | 4 ++-- >>>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/libavformat/mov.c b/libavformat/mov.c >>>>>> index 899690d920..c7422cd9ed 100644 >>>>>> --- a/libavformat/mov.c >>>>>> +++ b/libavformat/mov.c >>>>>> @@ -4340,8 +4340,8 @@ static int mov_read_trun(MOVContext *c, >>>>>> AVIOContext *pb, MOVAtom atom) >>>>>> MOV_FRAG_SAMPLE_FLAG_DEPENDS_YES)); >>>>>> if (keyframe) >>>>>> distance = 0; >>>>>> - ctts_index = av_add_index_entry(st, offset, dts, sample_size, >>>>>> distance, >>>>>> - keyframe ? AVINDEX_KEYFRAME : >>>>>> 0); >>>>>> + ctts_index = add_index_entry(st, offset, dts, sample_size, >>>>>> distance, >>>>>> + keyframe ? AVINDEX_KEYFRAME : 0); >>>>> can this lead to timestamps being out of order not just changing >>>>> from strictly monotone to monotone ? >>>>> >>>>> Maybe iam missing somehing but out of order could/would cause problems >>>>> with av_index_search_timestamp() and possibly others >>>>> >>>>> >>>> I'm not sure I understand the question. But I think I can answer. The >>>> new fragment can start before the last fragment >>>> ends. I'll make a concrete example. Lets say the new fragment's first DTS >>>> is 10 frames before the end of the previous >>>> fragment. So the first DTS of the new fragment is before the timestamp of >>>> 10 entries in the index from the previous >>>> fragment. av_add_index_entry searches the existing index and inserts the >>>> first sample of the new fragment in position >>>> nb_index_entries - 10 (and shifts the existing entries). The next 9 >>>> samples of the new fragment get intermixed with the >>>> remaining 9 samples of the previous fragment, sorted by DTS. When the >>>> samples are read out, you get samples from the >>>> last fragment and the new fragment interleaved together causing decoding >>>> errors. >>>> >>>> Using add_index_entry will result in the timestamps in the index going >>>> backwards by 10 frames at the fragment boundary >>>> in this example. In the other patch that accompanied this one, I've >>>> marked the samples from the new fragment that >>>> overlap previous samples with AVINDEX_DISCARD. ff_index_search_timestamp >>>> appears to be AVINDEX_DISCARD aware. So I >>>> think av_index_search_timestamp will do the right thing. >>> yes, that makes sense now. >>> Please correct me if iam wrong but then patch 1 would introduce a >>> issue that the 2nd fixes. So both patches should be merged to avoid >>> this >>> >>> But theres another problem, trun can be read out of order, when one >>> seeks around, so the next might have to be put elsewhere than after the >>> previous >>> >>> thanks >>> >> Hmm, can you describe the circumstances where this would happen. I looked >> at the seek code and can't see any way for it >> to seek to the middle somewhere without first reading previous trun. It >> looks to me like if avformat_seek_file or >> av_seek_frame fails to find the desired timestamp in the index it falls back >> to seek_frame_generic which seeks to the >> position of the last sample in the index and performs av_read_frame until it >> gets to the timestamp it wants. Is there a >> path I've missed where it can skip to the middle of the file somehow? > I used > -rw-r----- 1 michael michael 66908195 Dec 11 2015 buck480p30_na.mp4 > ./ffplay buck480p30_na.mp4 > > (i can upload this if needed, i dont know where its from exactly) > > and when seeking around by using the right mouse buttonq it sometimes read > trun chunks with lower times than previous (seen from the av_logs in > there) > > I hope i made no mistake and would assume this happens with any file > with these chunks > > ... > [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f3884000940] AVIndex stream 0, sample 151, > offset 60134, dts 450000, size 194, distance 25, keyframe 0 > ... > Seek to 68% ( 0:07:11) of total duration ( 0:10:34) > ... > [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f3884000940] AVIndex stream 0, sample 152, > offset 2b74fd6, dts 38757000, size 8284, distance 0, keyframe 1 > ... > Seek to 14% ( 0:01:29) of total duration ( 0:10:34) > ... > [mov,mp4,m4a,3gp,3g2,mj2 @ 0x7f3884000940] AVIndex stream 0, sample 152, > offset 959164, dts 7749000, size 55027, distance 0, keyframe 1 > >
When seeking mov_read_trun is getting called repeatedly for the same fragment which has a number of undesirable side effects, even without my patch. The following things get updated to incorrect values when seeking backward and the trun is re-read: sc->data_size sc->duration_for_fps sc->nb_frames_for_fps sc->track_end The trun is getting re-read in mov_switch_root because headers_read in MOVFragmentIndex has not yet been set for the fragment. I think a solution to this is to set headers_read for the appropriate entry in MOVFragmentIndex when the trun is read the first time. Does this sound like the right approach? -- John GnuPG fingerprint: D0EC B3DB C372 D1F1 0B01 83F0 49F1 D7B2 60D4 D0F7
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