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• Using a QUdpSocket for Custom FFMPEG I/O (raw H.264)

  19 avril 2012, par Bobby Ray

  I'm trying to create a custom I/O layer to pass raw H.264 frame data to FFMPEG from QUdpSocket datagrams. The H.264 frames don't have any sort of container and are simply streamed from the frame grabbing device. Something is going wrong, because for some reason FFMPEG thinks the access unit has a size of 1 when I call avcodec_decode_video2() :

  [h264 @ 0x1030dd000] missing picture in access unit with size 1
  
  [h264 @ 0x1030dd000] no frame!

  My first step is to probe the first frame for the AVInputFormat :

  socket->readDatagram(datagram.data(), datagram.size());
  
  
  
  AVProbeData probeData;
  
  probeData.filename = udpUrl.toStdString().c_str();
  
  probeData.buf_size = datagram.size() + AVPROBE_PADDING_SIZE;
  
  probeData.buf = (unsigned char *)malloc(datagram.size() + AVPROBE_PADDING_SIZE);
  
  memcpy(&probeData.buf[AVPROBE_PADDING_SIZE], datagram.data(), datagram.size());
  
  
  
  inputFormat = av_probe_input_format(&probeData, 1);

  Next I allocate an AVIOContext :

  buffer = (unsigned char *)malloc(bufferSize);
  
  ioContext = avio_alloc_context(buffer, bufferSize, 0, socket, &readFrame, NULL, NULL);

  After which I call avformat_open_input_stream() :

  if (av_open_input_stream(&formatContext, ioContext, "", inputFormat, NULL) != 0)

  Which seems to return successfully. However, the video stream is missing important information such as width, height, and pixel format, which then causes av_find_stream_info() to fail. I can set these parameters manually, but it doesn't result in a successful decode, and it makes me wonder what else I'm missing.

  From what I can tell, the NAL units are intact :

  First Frame
  
  00:00:00:01:27:64:00:28:ad:84:09:26:6e:23:34:90:81:24:cd:c4:66:92:10:24:99:b8:8c:d2:42:04:93:37:11:9a:48:40:92:66:e2:33:49:08:12:4c:dc:46:69:21:05:5a:eb:d7:d7:e4:fe:bf:27:d7:ae:b5:50:82:ad:75:eb:eb:f2:7f:5f:93:eb:d7:5a:ab:40:50:1e:c8:
  
  00:00:00:01:28:ee:3c:b0:
  
  00:00:00:01:25:88:84:27:...
  
  
  
  Second Frame
  
  00:00:00:01:21:9a:59:15:...

  Am I missing an API call ? Can anyone see something that I might be doing wrong ?

• Download hls stream without losing quality

  1er mars 2018, par Sinan Güler

  I tried using -i "input.m3u8" -codec:v copy -codec:a copy output.mp4
  The hls stream is in ts.

  I don’t think I’m getting the best quality, sometimes the video lags for a sec or two, audio is intact anyway.

  Am I using the right command line ?

• youtube-dl download one minute per every 5 minutes (on a twitch video, but i have the local file saved too if easier)

  18 mai 2016, par babadoctor

  I would like to do what the title says

  This is a ffmpeg command to download from a specific time in a video, offline or online.

  ffmpeg -ss (stop time) -i (direct video link) -t (start time) -c:v copy -c:a copy (title.mp4)

  I am going to be downloading this on OSX.
  I dont care what the title is.

  I think* there is a bash command that allows me to change the timings in this command up by a specific amount (+300 seconds per, the counter for start and stop time is in raw seconds)

  So, bash script that runs that command but increases the start and stop times incrementally by 300 (the stop timing being 60+ seconds ahead), downloads, then repeats.