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• How to send libmmpeg AVPacket through WebRTC (using libdatachannel)

  29 mars 2022, par mike

  I'm encoding a video frame with the ffmpeg libraries, generating an AVPacket with compressed data.

  


  Thanks to some recent advice here on S/O, I am trying to send that frame over a network using the WebRTC library libdatachannel, specifically by adapting the example here :

  


  https://github.com/paullouisageneau/libdatachannel/tree/master/examples/streamer

  


  I am seeing problems inside h264rtppacketizer.cpp (part of the library, not the example) which are almost certainly to do with how I'm providing the sample data.
(I don't think that this is anything to do with libdatachannel specifically, it will be an issue with what I'm sending)

  


  The example code reads each encoded frame from a file, and populates a sample by setting the content of the file to the contents of the file :

  


  sample = *reinterpret_cast *>(&fileContents);

  


  sample is just a std::vector<byte>;</byte>

  


  I have naively copied the contents of an AVPacket->data pointer into the sample vector :

  


  sample.resize(pkt->size);
memcpy(sample.data(), pkt->data, pkt->size * sizeof(std::byte));    


  


  but the packetizer is falling over when trying to get length values out of that data.
Specifically, in the following code, the first iteration gets a length of 1, but the second, looking up index 5, gives 1119887324. This is way too big for my data, which is only 3526 bytes (the whole frame is a single colour so likely to be small once encoded) :

  


  while (index &lt; message->size()) {&#xA;assert(index &#x2B; 4 &lt; message->size());&#xA;auto lengthPtr = (uint32_t *)(message->data() &#x2B; index);&#xA;uint32_t length = ntohl(*lengthPtr);&#xA;auto naluStartIndex = index &#x2B; 4;&#xA;auto naluEndIndex = naluStartIndex &#x2B; length;&#xA;assert(naluEndIndex &lt;= message->size());    &#xA;        &#xA;auto begin = message->begin() &#x2B; naluStartIndex;&#xA;auto end = message->begin() &#x2B; naluEndIndex;&#xA;nalus->push_back(std::make_shared<nalunit>(begin, end));&#xA;index = naluEndIndex;&#xA;}&#xA;</nalunit>

  


  Here is a dump of

  


  uint32_t length = ntohl(*lengthPtr);


  


  for the first few elements of the message (*lengthPtr in parentheses) :

  


  [2022-03-29 15:12:01.182] [info] index 0: 1  (16777216)
[2022-03-29 15:12:01.183] [info] index 1: 359  (1728118784)
[2022-03-29 15:12:01.184] [info] index 2: 91970  (1114046720)
[2022-03-29 15:12:01.186] [info] index 3: 23544512  (3225577217)
[2022-03-29 15:12:01.186] [info] index 4: 1732427807  (532693607)
[2022-03-29 15:12:01.187] [info] index 5: 1119887324  (3693068354)
[2022-03-29 15:12:01.188] [info] index 6: 3223313413  (98312128)
[2022-03-29 15:12:01.188] [info] index 7: 534512896  (384031)
[2022-03-29 15:12:01.188] [info] index 8: 3691315291  (1526728156)
[2022-03-29 15:12:01.189] [info] index 9: 83909537  (2707095557)
[2022-03-29 15:12:01.189] [info] index 10: 6004992  (10574592)
[2022-03-29 15:12:01.190] [info] index 11: 1537277952  (41307)
[2022-03-29 15:12:01.190] [info] index 12: 2701131779  (50331809)
[2022-03-29 15:12:01.192] [info] index 13: 768  (196608)


  


  (I know I should post a complete sample, I am working on it)

  


  


  • I am fairly sure I am just missing something basic. E.g. am I supposed to do something with the AVPacket side_data, does AVPacket have or miss some header info ?

    


  


  • If I just fwrite the pkt->data for a single frame to disk, I can read the codec information with ffprobe :

    


  


  


  Input #0, h264, from 'encodedOut.h264':
Duration: N/A, bitrate: N/A
Stream #0:0: Video: h264 (Constrained Baseline), yuv420p(progressive), 1280x720, 30 tbr, 1200k tbn


  


  

  • whereas the same for the example input files (again a single frame) gives the following :

  


  


  [h264 @ 000001c88d1135c0] Format h264 detected only with low score of 1, misdetection possible!
[h264 @ 000001c88f337400] missing picture in access unit with size 85306
[extract_extradata @ 000001c88d11ee40] No start code is found.
sample-0.h264: Invalid data found when processing input


  


• obs-studio build fails on Debian distros

  24 août 2021, par Fabian Druschke

  Ahoy ahoy.
Currently i am trying to compile obs-studio on my Debian machine (Debian Bullseye).
I have compiled FFMpeg myself in order to enable nvenc support for NVIDIA hardware acceleration.
Now i try to compile obs-studio but it always breaks at this error :

  


  [ 41%] Built target obs-x264
[ 42%] Built target obs-libfdk
[ 43%] Building C object plugins/obs-ffmpeg/CMakeFiles/obs-ffmpeg.dir/obs-ffmpeg-audio-encoders.c.o
In file included from /tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:27:
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-formats.h:3:47: error: unknown type name ‘AVCodecContext’; did you mean ‘AVFormatContext’?
    3 | static inline int64_t rescale_ts(int64_t val, AVCodecContext *context,
      |                                               ^~~~~~~~~~~~~~
      |                                               AVFormatContext
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c: In function ‘convert_speaker_layout’:
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:65:10: error: ‘AV_CH_LAYOUT_MONO’ undeclared (first use in this function)
   65 |   return AV_CH_LAYOUT_MONO;
      |          ^~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:65:10: note: each undeclared identifier is reported only once for each function it appears in
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:67:10: error: ‘AV_CH_LAYOUT_STEREO’ undeclared (first use in this function)
   67 |   return AV_CH_LAYOUT_STEREO;
      |          ^~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:69:10: error: ‘AV_CH_LAYOUT_SURROUND’ undeclared (first use in this function)
   69 |   return AV_CH_LAYOUT_SURROUND;
      |          ^~~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:71:10: error: ‘AV_CH_LAYOUT_4POINT0’ undeclared (first use in this function)
   71 |   return AV_CH_LAYOUT_4POINT0;
      |          ^~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:73:10: error: ‘AV_CH_LAYOUT_4POINT1’ undeclared (first use in this function)
   73 |   return AV_CH_LAYOUT_4POINT1;
      |          ^~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:75:10: error: ‘AV_CH_LAYOUT_5POINT1_BACK’ undeclared (first use in this function)
   75 |   return AV_CH_LAYOUT_5POINT1_BACK;
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:77:10: error: ‘AV_CH_LAYOUT_7POINT1’ undeclared (first use in this function)
   77 |   return AV_CH_LAYOUT_7POINT1;
      |          ^~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c: In function ‘convert_ff_channel_layout’:
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:88:7: error: ‘AV_CH_LAYOUT_MONO’ undeclared (first use in this function)
   88 |  case AV_CH_LAYOUT_MONO:
      |       ^~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:90:7: error: ‘AV_CH_LAYOUT_STEREO’ undeclared (first use in this function)
   90 |  case AV_CH_LAYOUT_STEREO:
      |       ^~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:92:7: error: ‘AV_CH_LAYOUT_SURROUND’ undeclared (first use in this function)
   92 |  case AV_CH_LAYOUT_SURROUND:
      |       ^~~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:94:7: error: ‘AV_CH_LAYOUT_4POINT0’ undeclared (first use in this function)
   94 |  case AV_CH_LAYOUT_4POINT0:
      |       ^~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:96:7: error: ‘AV_CH_LAYOUT_4POINT1’ undeclared (first use in this function)
   96 |  case AV_CH_LAYOUT_4POINT1:
      |       ^~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:98:7: error: ‘AV_CH_LAYOUT_5POINT1_BACK’ undeclared (first use in this function)
   98 |  case AV_CH_LAYOUT_5POINT1_BACK:
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:100:7: error: ‘AV_CH_LAYOUT_7POINT1’ undeclared (first use in this function)
  100 |  case AV_CH_LAYOUT_7POINT1:
      |       ^~~~~~~~~~~~~~~~~~~~
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c: In function ‘enc_create’:
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:205:13: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  205 |  enc->codec = avcodec_find_encoder_by_name(type);
      |             ^
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:209:14: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  209 |   enc->codec = avcodec_find_encoder_by_name(alt);
      |              ^
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c: In function ‘do_encode’:
/tmp/obs-studio/plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c:343:16: error: implicit declaration of function ‘rescale_ts’ [-Werror=implicit-function-declaration]
  343 |  packet->pts = rescale_ts(avpacket.pts, enc->context, time_base);
      |                ^~~~~~~~~~
cc1: some warnings being treated as errors
make[2]: *** [plugins/obs-ffmpeg/CMakeFiles/obs-ffmpeg.dir/build.make:95: plugins/obs-ffmpeg/CMakeFiles/obs-ffmpeg.dir/obs-ffmpeg-audio-encoders.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:1381: plugins/obs-ffmpeg/CMakeFiles/obs-ffmpeg.dir/all] Error 2
make: *** [Makefile:171: all] Error 2


  


  I didn't find any fixes yet. So i thought i was clever, so i set up a Debian Sid virtual machine and instead of using the git, i used apt source obs-studio and apt build-dep obs-studio. Unfortunately the result was the same, dpkg-buildpackage -rfakeroot -b -uc -us had the same result, in the same file : obs-ffmpeg-audio-encoders.c
What might be the issue here ? Did i miss something fundamental ? Thanks in advance friends !

  


• ffmpeg, /dev/video0, -f decklink

  20 mars 2019, par Camille Goudeseune

  I’m trying to capture video from a PCI card, the Blackmagic DeckLink Mini Recorder, via ffmpeg, on a headless host running Ubuntu 18.04.2 LTS, hopefully with a command like

  ffmpeg -f decklink -i /dev/video0 ...

  How can I make that work ? I have two obstacles.

  No /dev/video0

  ffmpeg -i /dev/video0 ... fails : /dev/video0: No such device or address.
  v4l2-ctl --list-devices fails with the same error message.

  I built /dev/video0, and it looks okay :

  mknod /dev/video0 c 81 0
  
  chown root.video /dev/video0
  
  chmod g+rw /dev/video0

  To compare this file with a working one, I ran strace cat /dev/video0 on this host, and on another host (Ubuntu 14) with a working /dev/video0. The outputs began to differ here (good, then bad) :

  fstat(1, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
  
  open("/dev/video0", O_RDONLY)           = 3  
  
  fstat(3, {st_mode=S_IFCHR|0660, st_rdev=makedev(81, 0), ...}) = 0
  
  fadvise64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0
  
  ----
  
  
  
  fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
  
  openat(AT_FDCWD, "/dev/video0", O_RDONLY) = -1 ENXIO (No such device or address)

  So /dev/video0 is broken at a level lower than ffmpeg or v4l2 or even cat.

  On Ubuntu 14, man 8 MAKEDEV suggests that the error message means that "the kernel does not have the driver configured or loaded."

  This Ubuntu 18 host lacks that manpage, but it does have a few /snap/core/*/sbin/MAKEDEV, all the same, so I tried

  /snap/core/6350/sbin/MAKEDEV -n -v video

  It would have created over a hundred devices videoXX, radioXX, vtxXX, vbiXX. Those devices didn’t exist yet, so it seemed harmless to try it.

  rm /dev/video0; /snap/core/6350/sbin/MAKEDEV video

  That rebuilt /dev/video0, but "No such device" remains, from cat or ffmpeg.

  No decklink

  ffmpeg -f decklink ... fails with Unknown input format: 'decklink'.

  Neither black nor deck nor link is mentioned by ffmpeg -devices (fbdev, lavfi, oss, v4l2) and ffmpeg -formats (about 350), either for Ubuntu’s own version 3.4.4-0ubuntu0.18.04.1, or for version N-93330-g7ff89574c7 compiled from source on 2019 Mar 13 :

  git clone https://git.ffmpeg.org/ffmpeg.git ffmpeg
  
  cd ffmpeg
  
  ./configure --enable-nonfree --disable-doc --disable-w32threads --enable-pthreads

  (Although ./configure --help mentions --enable-decklink, using that yielded "ERROR : DeckLinkAPI.h not found." updatedb && locate DeckLinkAPI.h finds no file with that name, either.)

  The DeckLink PCI card is recognized by hwinfo and lspci.

  lsmod reports the loaded modules blackmagic and blackmagic_io.

  Maybe the PCI card is installed ok, but ffmpeg just can’t reach it because I can’t configure it for that.

  Edit : Rebooting didn’t fix anything.