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• FFmpeg CLI - transcode only if necessary

  23 septembre 2018, par Tyrrrz

  I want to mux an audio and video stream into a single video file. These two streams come in arbitrary formats. Sometimes the input and output encodings will match, in which case I would want to save a lot of processing time by using -c copy argument that tells FFmpeg to avoid transcoding.

  Is there a way to tell FFmpeg to automatically determine if transcoding is required, based on the formats of input files ? Alternatively, I can do the check myself, but I would prefer for FFmpeg to do in on its own, if possible.

• How can I find out what this ffmpeg error code means ?

  27 septembre 2018, par Asik

  I’m using the function avcodec_decode_video2. On an encoding change in the stream, it returns -1094995529. The documentation only states :

  On error a negative value is returned, otherwise the number of bytes
  used or zero if no frame could be decompressed.

  But there doesn’t seem to be an enum of return codes or any other form of documentation. What does the error mean and how can I determine that in general ?

• FFMPEG intermittent failures reading live RTMP stream

  22 janvier 2019, par stevendesu

  The Command

  I’m attempting to read a live RTMP stream and save the result to a file with the following command :

  ffmpeg -re -rtmp_live live -y -i "rtmp://<server>/<app>/<stream>" -c copy -f flv /tmp/dump.flv
  
  </stream></app></server>

  I run this command then after 10-15 seconds I kill the process and check /tmp/dump.flv. I’m trying to do this for stream diagnostic purposes (determine the encoding, bitrate, resolution, pixel format, and key frame interval of the live stream)

  This command works about 25-50% of the time. When it works FFMPEG takes about 5 seconds to connect to the stream, then it begins dumping data to disk. After I kill the process, I can find a couple of megabytes of video data in /tmp/dump.flv which can be probed using ffprobe.

  When the command fails, it goes into one of two failure states :

  Failure State 1

  stderr is flooded with a series of messages about "missing picture in access unit with size X", and the output file /tmp/dump.flv is created but contains 0 bytes

  ffmpeg version 3.4.4-1~16.04.york0 Copyright (c) 2000-2018 the FFmpeg developers
  
    built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
  
    configuration: --prefix=/usr --extra-version='1~16.04.york0' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 78.100 / 55. 78.100
  
    libavcodec     57.107.100 / 57.107.100
  
    libavformat    57. 83.100 / 57. 83.100
  
    libavdevice    57. 10.100 / 57. 10.100
  
    libavfilter     6.107.100 /  6.107.100
  
    libavresample   3.  7.  0 /  3.  7.  0
  
    libswscale      4.  8.100 /  4.  8.100
  
    libswresample   2.  9.100 /  2.  9.100
  
    libpostproc    54.  7.100 / 54.  7.100
  
  [NULL @ 0x55b72d568920] pps_id 381 out of range
  
  [AVBSFContext @ 0x55b72d5692c0] Invalid NAL unit 0, skipping.
  
      Last message repeated 1 times
  
  [h264 @ 0x55b72d568920] Invalid NAL unit 0, skipping.
  
      Last message repeated 1 times
  
  [h264 @ 0x55b72d568920] no frame!
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2200
  
  [AVBSFContext @ 0x55b72d5692c0] Invalid NAL unit 0, skipping.
  
      Last message repeated 2 times
  
  [h264 @ 0x55b72d568920] Invalid NAL unit 0, skipping.
  
      Last message repeated 2 times
  
  [h264 @ 0x55b72d568920] no frame!
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 3171
  
  [AVBSFContext @ 0x55b72d5692c0] Invalid NAL unit 0, skipping.
  
  [h264 @ 0x55b72d568920] Invalid NAL unit 0, skipping.
  
  [h264 @ 0x55b72d568920] no frame!
  
  [NULL @ 0x55b72d568920] missing picture in access unit with size 80572
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 1560
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2608
  
  [h264 @ 0x55b72d568920] non-existing PPS 0 referenced
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2734
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2885
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 77739
  
  [h264 @ 0x55b72d568920] non-existing PPS 254 referenced
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 3360
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2804
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 3051
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 3067
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 77693
  
  [h264 @ 0x55b72d568920] non-existing PPS 0 referenced
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2421
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2779
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2442
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2678
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 76877
  
  [h264 @ 0x55b72d568920] sps_id 15 out of range
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 1342
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2412
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 2238
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 3550
  
  [h264 @ 0x55b72d568920] missing picture in access unit with size 3075
  
  ...
  
  (after hitting Ctrl+C:)
  
  Input #0, flv, from 'rtmp://<server>/<app>/<stream>':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.83.100
  
    Duration: 00:00:00.00, start: 5285.919000, bitrate: N/A
  
      Stream #0:0: Video: h264 (Constrained Baseline), yuv420p, 1920x1080, 2543 kb/s, 24 fps, 24 tbr, 1k tbn, 48 tbc
  
  Output #0, flv, to '/tmp/dump.flv':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.83.100
  
      Stream #0:0: Video: h264 (Constrained Baseline) ([7][0][0][0] / 0x0007), yuv420p, 1920x1080, q=2-31, 2543 kb/s, 24 fps, 24 tbr, 1k tbn, 1k tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
  Press [q] to stop, [?] for help
  
  frame=    0 fps=0.0 q=-1.0 Lsize=       0kB time=00:00:00.00 bitrate=N/A speed=   0x
  
  video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
  
  Exiting normally, received signal 2.
  
  </stream></app></server>

  Failure State 2

  The message "No start code is found." is displayed and FFMPEG immediately terminates after less than a half-second. When this happens the file /tmp/dump.flv is not created.

  ffmpeg version 3.4.4-1~16.04.york0 Copyright (c) 2000-2018 the FFmpeg developers
  
    built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
  
    configuration: --prefix=/usr --extra-version='1~16.04.york0' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 78.100 / 55. 78.100
  
    libavcodec     57.107.100 / 57.107.100
  
    libavformat    57. 83.100 / 57. 83.100
  
    libavdevice    57. 10.100 / 57. 10.100
  
    libavfilter     6.107.100 /  6.107.100
  
    libavresample   3.  7.  0 /  3.  7.  0
  
    libswscale      4.  8.100 /  4.  8.100
  
    libswresample   2.  9.100 /  2.  9.100
  
    libpostproc    54.  7.100 / 54.  7.100
  
  [NULL @ 0x56274b0be920] missing picture in access unit with size 3710
  
  [AVBSFContext @ 0x56274b0bf2c0] No start code is found.
  
  rtmp://<server>/<app>/<stream>: could not find codec parameters
  
  Input #0, flv, from 'rtmp://<server>/<app>/<stream>':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.83.100
  
    Duration: 00:00:00.00, start: 0.000000, bitrate: N/A
  
      Stream #0:0: Video: h264, none, 2543 kb/s, 24 fps, 1k tbn
  
  Output #0, flv, to '/tmp/dump.flv':
  
  Output file #0 does not contain any stream
  
  </stream></app></server></stream></app></server>

  What I’ve tried

  • Adding or removing -re to try and limit the input frame rate to the source frame rate
  • Adding or removing -rtmp_live live
  • Adding or removing -timeout 5 (or any other timeout value)
  • Using RTMP URL parameters (e.g. -i "rtmp://<server>/<app>/<stream> live=1 timeout=5"</stream></app></server>)

  Does anyone know why this command’s success is so intermittent or how I can get more consistent results ?

  Alternate Acceptable Solution

  The only reason I’m using ffmpeg to dump the stream to a temporary file at all is because I plan to perform multiple tests on the file (at least two at the moment — one to get the encoding, and another to get the key frame interval). By downloading the stream I reduce bandwidth usage and reduce runtime. However it’s perfectly acceptable to forego ffmpeg and just use ffprobe directly on the RTMP URL if this would help.

  Note that I did try this and I get the same two failure states with ffprobe