CODEWITHSUNDEEP
ffmpeg
Mukund Manikarnike
Mukund Manikarnike

Reputation: 397

ffmpeg demux into audio and video resets PTS

Demuxing

I am demuxing TS segments into audio and video as follows.

ffmpeg -y -i input.ts -vcodec copy -an output_video.ts
ffmpeg -y -i input.ts -acodec copy -vn output_audio.aac

Inspecting Input

The start_pts and start_time on input.ts are as shown below. I was able to inspect these values using ffprobe -show_streams -print_format json input.ts

"start_pts": 8306558438,
"start_time": "92295.093756",

Inspecting output video

The output .ts has some default start_pts and start_time values as shown below. These were also obtained using the same ffprobe command as indicated above.

"start_pts": 126000,
"start_time": "1.400000",

Inspecting output audio

The same ffprobe command on output_audio.aac shows that the output aac has invalid codec_tag and codec_tag_string as shown below. The start_pts and start_time are not present in the output_audio.aac. 

"codec_tag_string": "[0][0][0][0]", (should have been [15][0][0][0])
"codec_tag": "0x0000", (should have been 0xf000)

Questions

  1. Wondering if this difference in the start_pts, start_time, codec_tag is expected?
  2. If it is expected, what can I do to ensure that the all of these parameters get retained on the output?
  3. If it is not expected, is there some more information I can share to track this down?

Note

There were other outputs that I found inconsistent in the ffprobe command for the output_audio.aac like duration etc.. I shared what I thought are most valuable at this point. If required I can share complete outputs from all of the above executions.

[EDIT 07/30/2018 - 08:00 MST] logs for ffmpeg -y -i input.ts -vcodec copy -an output_video.ts -acodec copy -vn output_audio.aacare as shown below.

ffmpeg version 4.0.2 Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.0.2 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-ffplay --enable-frei0r --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-librtmp --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma --enable-libopenjpeg --disable-decoder=jpeg2000 --extra-cflags=-I/usr/local/Cellar/openjpeg/2.3.0/include/openjpeg-2.3 --enable-nonfree
  libavutil      56. 14.100 / 56. 14.100
  libavcodec     58. 18.100 / 58. 18.100
  libavformat    58. 12.100 / 58. 12.100
  libavdevice    58.  3.100 / 58.  3.100
  libavfilter     7. 16.100 /  7. 16.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  1.100 /  5.  1.100
  libswresample   3.  1.100 /  3.  1.100
  libpostproc    55.  1.100 / 55.  1.100
[mpegts @ 0x7f88ed803000] start time for stream 0 is not set in estimate_timings_from_pts
Input #0, mpegts, from 'i7h9456s_media_46185.ts':
  Duration: 00:00:06.05, start: 86216.852667, bitrate: 2898 kb/s
  Program 1 
    Stream #0:0[0x102]: Data: timed_id3 (ID3  / 0x20334449)
    Stream #0:1[0x100]: Video: h264 (Constrained Baseline) ([27][0][0][0] / 0x001B), yuv420p(tv, smpte170m, progressive), 640x360 [SAR 1:1 DAR 16:9], 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
    Stream #0:2[0x101]: Audio: aac (LC) ([15][0][0][0] / 0x000F), 44100 Hz, stereo, fltp, 190 kb/s
Output #0, mpegts, to '../output_video.ts':
  Metadata:
    encoder         : Lavf58.12.100
    Stream #0:0: Video: h264 (Constrained Baseline) ([27][0][0][0] / 0x001B), yuv420p(tv, smpte170m, progressive), 640x360 [SAR 1:1 DAR 16:9], q=2-31, 29.97 fps, 29.97 tbr, 90k tbn, 90k tbc
Output #1, adts, to '../output_audio.aac':
  Metadata:
    encoder         : Lavf58.12.100
    Stream #1:0: Audio: aac (LC) ([15][0][0][0] / 0x000F), 44100 Hz, stereo, fltp, 190 kb/s
Stream mapping:
  Stream #0:1 -> #0:0 (copy)
  Stream #0:2 -> #1:0 (copy)
Press [q] to stop, [?] for help
frame=  180 fps=0.0 q=-1.0 Lsize=    2088kB time=00:00:06.03 bitrate=2833.8kbits/s speed= 904x    
video:1918kB audio:142kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.349750%

Upvotes: 2

Views: 3733

Answers (1)

Gyan
Gyan

Reputation: 93299

All the differences are expected. FFmpeg removes input timestamp offset unless set otherwise. The MPEG-TS muxer also adds a timestamp offset.

You can preserve source timestamps when remuxing TS, and also avoid the muxer's offset, like this,

ffmpeg -y -copyts -i input.ts -vcodec copy -an -muxdelay 0 -muxpreload 0 output_video.ts

As .aac is a raw ADTS stream, there is no codec tag string present. This is expected. Mux to .m4a or .mka or a similar container if tags are needed.

Upvotes: 4

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