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• Simultaneous fragmentation and video encoding FFMPEG

  20 mai 2020, par Искандер

  Good day !
I encrypted and fragmented .mp4 video file, but after encryption, I can't decode it back. Could you tell me please what I'm doing wrong ?
Command, which I use to encrypt :

  



  ffmpeg -i C:\ffmpeg-3.2.2-win64-static\111.mp4 -vcodec copy -acodec copy -encryption_scheme cenc-aes-ctr -encryption_key 76a6c65c5ea762046bd749a2e632ccbb -encryption_kid a7e61c373e219033c21091fa607bf3b8 -g 52 -f mp4 -movflags frag_keyframe+empty_moov C:\ffmpeg-3.2.2-win64-static\result.mp4


  



  Command, which I use to decode :

  



  ffmpeg -decryption_key 76a6c65c5ea762046bd749a2e632ccbb -i C:\ffmpeg-3.2.2-win64-static\resultfragm.mp4 -max_muxing_queue_size 9999 C:\ffmpeg-3.2.2-win64-static\resultlast.mp4


  



  Result :

  



  Result image

  


• FFmpeg SwrContext incorrectly converting leftover data after seek

  27 avril 2017, par trigger_death

  I currently have my own custom SFML SoundFileReader that uses FFmpeg for more file formats. It works great for the most part until you seek and then you get leftover data from the previous location when using swr_convert. I currently have a hackish (I think) solution to the problem where I call swr_init after seeking to remove whatever data is leftover in there. I assumed that swr_convert’s documentation on flushing would be the solution to the issue yet either it doesn’t help or I’m not doing it correctly. Is there a proper way to clear the leftover data in the SwrContext after seeking ?

  void seekBeginning() {
  
      av_seek_frame(
  
          m_formatContext, m_audioStream,
  
          m_formatContext->streams[m_audioStream]->first_dts,
  
          AVSEEK_FLAG_BACKWARD | AVSEEK_FLAG_ANY
  
      );
  
      avcodec_flush_buffers(m_codecContext);
  
  
  
      // This fixes the issue but it seems like a horribly incorrect way of doing it
  
      swr_init(m_convertContext);
  
  
  
      // I've tried this but it doesn't seem to work
  
      //swr_convert(m_convertContext, NULL, 0, NULL, 0);
  
  }
  
  
  
  Uint64 read(Int16* samples, Uint64 maxCount) {
  
      Uint64 count = 0;
  
      while (count < maxCount) {
  
          if (m_packet->stream_index == m_audioStream) {
  
              while (m_packet->size > 0) {
  
                  int gotFrame = 0;
  
                  int result = avcodec_decode_audio4(m_codecContext, m_frame, &gotFrame, m_packet);
  
                  if (result >= 0 && gotFrame) {
  
                      int samplesToRead = static_cast<int>(maxCount - count) / m_codecContext->channels;
  
                      if (samplesToRead > m_frame->nb_samples)
  
                          samplesToRead = m_frame->nb_samples;
  
                      m_packet->size -= result;
  
                      m_packet->data += result;
  
                      result = swr_convert(m_convertContext, (uint8_t**)&amp;samples, samplesToRead, (const uint8_t**)m_frame->data, m_frame->nb_samples);
  
  
  
                      if (result > 0) {
  
                          count += result * m_codecContext->channels;
  
                          samples += result * m_codecContext->channels;
  
                      }
  
                      else {
  
                          m_packet->size = 0;
  
                          m_packet->data = NULL;
  
                      }
  
                  }
  
                  else {
  
                      m_packet->size = 0;
  
                      m_packet->data = NULL;
  
                  }
  
              }
  
          }
  
          av_free_packet(m_packet);
  
      }
  
  
  
      return count;
  
  }
  
  </int>

• Concatenating chunks of videos with different formats using FFmpeg

  12 avril 2014, par SCC

  I was exploring the functionalities of FFmpeg recently. I have two different videos with different formats (e.g. mov and mp4). I will first split these videos up into smaller chunks, and concatenate them back with a mix of chunks from these two videos. However the concatenated video wasn't able to show properly. I did some research and found that mp4 cannot be concatenated using the normal concatenation method since it contains extra headers and information. Therefore I first converted all the videos into mpg, split them up, concatenate an convert back to mp4. However, still no luck on that.

  Below are the commands I used :

  // convert input (1st video) to mpg
  
  ffmpeg -i input.mp4 input.mpg
  
  
  
  // convert to keyframe video
  
  ffmpeg -i input.mpg -strict -2 -g 20 keyframe_input.mpg
  
  
  
  // split keyframe_input into smaller chunks
  
  ffmpeg -i keyframe_input.mpg -acodec copy -f segment -segment_time 0.3 -segment_list  s.m3u8 -vcodec copy -reset_timestamps 1 -map 0 split_input-%d.mpg
  
  
  
  // convert input2 (2nd video) to mpg
  
  ffmpeg -i input2.mov input2.mpg
  
  
  
  // convert to keyframe video
  
  ffmpeg -i input2.mpg -strict -2 -g 20 keyframe_input2.mpg
  
  
  
  // split keyframe_input2 into smaller chunks
  
  ffmpeg -i keyframe_input2.mpg -acodec copy -f segment -segment_time 0.3 -segment_list  s.m3u8 -vcodec copy -reset_timestamps 1 -map 0 split_input2-%d.mpg
  
  
  
  // concatenate video according to the video files written in mylist.txt
  
  ffmpeg -f concat -i mylist.txt -c copy output.mpg

  When I tried to concatenate these chunks of videos, errors were thrown out saying buffer underflow, packet size too large.

  These are parts of the errors I had. I am not really sure about which errors refer to which video (either input.mp4 or input2.mov), but this is what I had :

  [mpeg @ 0x7f972406ca00] Non-monotonous DTS in output stream 0:0; previous: 2953328, current: 2541459; changing to 2953329. This may result in incorrect timestamps in the output file.
  
  [mpeg @ 0x7f972406ca00] Non-monotonous DTS in output stream 0:0; previous: 2953329, current: 2545059; changing to 2953330. This may result in incorrect timestamps in the output file.
  
  [mpeg @ 0x7f972406ca00] Non-monotonous DTS in output stream 0:0; previous: 2953330, current: 2548659; changing to 2953331. This may result in incorrect timestamps in the output file.
  
  [mpeg @ 0x7f972406ca00] Non-monotonous DTS in output stream 0:0; previous: 2953331, current: 2552259; changing to 2953332. This may result in incorrect timestamps in the output file.
  
  
  
  
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=7973 size=8360
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=923 size=954
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=2538 size=7686
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=4579 size=7686
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=6620 size=7686
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=339 size=511
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=721 size=2766
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=2762 size=2766
  
  [mpeg @ 0x7f972406ca00] buffer underflow st=0 bufi=988 size=1814

  Does any experts know why this happens ?