Wu Zhiqiang (2017-12-30): > Normally pts_wrap_reference is based on the first packet when calling > ff_read_packet, > which will call function update_wrap_reference , in libavformat/utils line > 734: > > if (ref == AV_NOPTS_VALUE) > ref = pkt->pts; > if (st->pts_wrap_reference != AV_NOPTS_VALUE || st->pts_wrap_bits >= 63 > || ref == AV_NOPTS_VALUE || !s->correct_ts_overflow) > return 0; > ref &= (1LL << st->pts_wrap_bits)-1; > > // reference time stamp should be 60 s before first time stamp > pts_wrap_reference = ref - av_rescale(60, st->time_base.den, > st->time_base.num); > > Because concat_read_header and concat_seek do not call ff_read_packet and > open_file does not copy pts_wrap_reference, > it is constant value during playing. > > If demuxing packets like avformat_open_input => avformat_seek_file => > av_read_frame and seek time is larger than 60s, > the constant reference time will be positive value and not indicate the > normal wrap margin. > > Then seeking to time before pts_wrap_reference may generate huge timestamp, > which not expected.
Thanks for explaining, but it still does not address my concern. I probably explained it badly. Let me try to rephrase. When an application is reading directly from a file, if I understand correctly, here is what happens: 1. file contains wrapped timestamps; 2. demuxer sets wrapping_bits to enable timestamps correction; 3. demuxer outputs packets with non-monotonic timestamps; 4. lavf sees non-monotonic timestamps; 5. lavf detects wrapping reference; 6. lavf fixes non-monotonic timestamps; 7. lavf returns packets with monotonic timestamps; 8. application sees packets with monotonic timestamps; 9. application has nothing to do at all about wrapping. Is it right? The concat demuxer behaves like any application. Therefore, I can copy-paste and rename: 1. file contains wrapped timestamps; 2. slave demuxer sets wrapping_bits to enable timestamps correction; 3. slave demuxer outputs packets with non-monotonic timestamps; 4. lavf for slave demuxer sees non-monotonic timestamps; 5. lavf for slave demuxer detects wrapping reference; 6. lavf for slave demuxer fixes non-monotonic timestamps; 7. lavf for slave demuxer returns packets with monotonic timestamps; 8. concat sees packets with monotonic timestamps; 9. concat has nothing to do at all about wrapping. And it should still be right. Note the conclusion: concat has nothing to do at all about wrapping. I will try to rephrase yet another way: Wrapped timestamps should be de-wrapped even before concat sees them, and thus no de-wrapping should be necessary after concat. Regards, -- Nicolas George
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