[mythtv-commits] Ticket #12010: mythcommflag --rebuild does not re-create good seektables with h264 recordings

[MythTV]

#12010: mythcommflag --rebuild does not re-create good seektables with h264
recordings
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 Reporter:  J.Pilk@…                     |          Owner:  pbennett
     Type:  Bug Report - General         |         Status:  assigned
 Priority:  minor                        |      Milestone:  unknown
Component:  MythTV - Video Decoding      |        Version:  Master Head
 Severity:  medium                       |     Resolution:
 Keywords:  mythcommflag --rebuild h264  |  Ticket locked:  0
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Comment (by blm-ubunet@…):

 The seektable generated for your latest sample looks right in cut-list
 editor.

 Broadcast TS files typically have offset between audio & video packets
 (with matching PTS) to allow post processing time for de-iterlace etc.

 You'll notice that mpv & VLC start typical broadcast TS recording playback
 with audio & no video because there is no video packet with matching PTS
 at start.

 AFAIU MythTV uses video PTS as time zero & mkvtoolnix & ffmpeg etc use
 earliest (time) PTS as time zero & this will be audio PTS in our
 recordings.
 I confirmed this behaviour of mkvtoolnix with the author.
 This is why "losslesscut" (mkvtoolnix time based) works fine with HDPVR
 recordings (60p samples seem to have 10's ms AV pkt PTS delta) & was never
 frame accurate for real-world broadcast TS files.
 I do have one sample 50p recording believed to be HDPVR that has 4 second
 delta audio to video!

 The TS cutting script, that I use, is file-offset based & is frame
 accurate & as fast as file copy. It just does not handle the AV pkt PTS
 delta.

 Your file has about 0.7sec (18 frame intervals) packet PTS delta. Could
 this time delta be the frame offset error you see with external cutting
 tool?
 You can extract this time delta with mediainfo & use it to offset the
 keyframe times.

 Have wondered if re-muxing TS recordings first to remove the AV delta &
 then generating cut-list would eliminate most problems of frame accuracy.

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Ticket URL: <https://code.mythtv.org/trac/ticket/12010#comment:20>
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