[FFmpeg-trac] #9921(avformat:new): DASH has duplicate AAC timestamp

[FFmpeg]

#9921: DASH has duplicate AAC timestamp
----------------------------------+---------------------------------------
             Reporter:  philipn   |                     Type:  defect
               Status:  new       |                 Priority:  normal
            Component:  avformat  |                  Version:  unspecified
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
----------------------------------+---------------------------------------
 Summary of the bug:
 Creating a DASH output from AAC with priming results in a duplicate
 timestamp in the second segment. The earliest presentation time of the
 second segment does not equal 0 + the duration of the first segment; it is
 off by 1 frame.

 The issue results from the code block at
 [https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/movenc.c#L5022]
 that sets the presentation time to 0. The workaround is to store that
 initial offset and add it back to the following presentation times at
 [https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/movenc.c#L5016]

 How to reproduce:
 Create a DASH output containing AAC, dump the packets and show there is a
 duplicate pts at the first sample in the second segment (pts = 238592).

 {{{
 % ffmpeg -f lavfi -i "sine=sample_rate=48000:frequency=1000:duration=10"
 -codec:a aac -f dash test.mpd
 Input #0, lavfi, from 'sine=sample_rate=48000:frequency=1000:duration=10':
   Duration: N/A, start: 0.000000, bitrate: 768 kb/s
   Stream #0:0: Audio: pcm_s16le, 48000 Hz, mono, s16, 768 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le (native) -> aac (native))
 Press [q] to stop, [?] for help
 [dash @ 0x7fa93a7e7900] Opening 'init-stream0.m4s' for writing
 Output #0, dash, to 'test.mpd':
   Metadata:
     encoder         : Lavf59.16.100
   Stream #0:0: Audio: aac, 48000 Hz, mono, fltp, 69 kb/s
     Metadata:
       encoder         : Lavc59.18.100 aac
 [dash @ 0x7fa93a7e7900] Opening 'chunk-stream0-00001.m4s.tmp' for writing
 [dash @ 0x7fa93a7e7900] Opening 'test.mpd.tmp' for writing
 [dash @ 0x7fa93a7e7900] Opening 'chunk-stream0-00002.m4s.tmp' for writing
 [dash @ 0x7fa93a7e7900] Opening 'test.mpd.tmp' for writing
 size=N/A time=00:00:10.00 bitrate=N/A speed=62.2x
 video:0kB audio:85kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown

 % ffprobe -show_packets test.mpd | grep pts=238592
 Input #0, dash, from 'test.mpd':
   Duration: 00:00:10.00, start: -0.021333, bitrate: 1 kb/s
   Program 0
     Stream #0:0: Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono,
 fltp, 69 kb/s
     Metadata:
       variant_bitrate : 69000
       id              : 0
 pts=238592
 pts=238592

 % ffmpeg -version
 ffmpeg version 5.0.1 Copyright (c) 2000-2022 the FFmpeg developers
 built with gcc 10.2.1 (Alpine 10.2.1_pre1) 20201203
 configuration: --disable-debug --disable-doc --disable-ffplay --enable-
 fontconfig --enable-gpl --enable-libaom --enable-libaribb24 --enable-
 libass --enable-libbluray --enable-libfdk_aac --enable-libfreetype
 --enable-libkvazaar --enable-libmp3lame --enable-libopencore-amrnb
 --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-
 libsrt --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-
 libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb
 --enable-libxvid --enable-libzmq --enable-nonfree --enable-openssl
 --enable-postproc --enable-shared --enable-small --enable-version3
 --extra-cflags=-I/opt/ffmpeg/include --extra-ldflags=-L/opt/ffmpeg/lib
 --extra-libs=-ldl --extra-libs=-lpthread --prefix=/opt/ffmpeg
 libavutil      57. 17.100 / 57. 17.100
 libavcodec     59. 18.100 / 59. 18.100
 libavformat    59. 16.100 / 59. 16.100
 libavdevice    59.  4.100 / 59.  4.100
 libavfilter     8. 24.100 /  8. 24.100
 libswscale      6.  4.100 /  6.  4.100
 libswresample   4.  3.100 /  4.  3.100
 libpostproc    56.  3.100 / 56.  3.100
 }}}
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9921>
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