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• Saving frames in different formats yields different MSE

  8 septembre 2022, par Mattia

  I am trying to find the frame in a video that is the most different from its previous and next one. Selecting this frame would give me the best chance of synchronizing two videos coming from different sources.
I am using the psnr filter between the target video and its delayed version, i.e., with ss=1/fps.

  


  Everything seems to work, but something strange happens when I am trying to see which frame (and surrounding frames) was chosen.

  


  I extract the frames as follows :

  


  ffmpeg -ss  -i  -frames 1 tmp/.png -y


  


  Doing this for the 2 frames before and the 2 frames after the selected frame, I get mse_avg and psnr_avg from the psnr filter as follows :

  


  mse_avg  psnr_avg          comment
2099.68     14.91     prev2 - prev
3365.92     12.86  prev - keyframe
2716.40     13.79  keyframe - next
2581.58     14.01     next - next2


  


  Instead, when dealing with the video, as well as when extracting single frames in .mp4 format I get :

  


  mse_avg  psnr_avg          comment
 942.57     18.39     prev2 - prev
1611.20     16.06  prev - keyframe
1348.51     16.83  keyframe - next
1208.34     17.31     next - next2


  


  I thought that saving frames in lossless image format would preserve their visual characteristics, thus providing the same performance.
Why does changing the frame output to PNG format yield different MSE ?

  


• Can't hear the audio rtp streaming

  18 juillet 2016, par starter

  i am trying to get the streaming audio from my computer’s mic to my tablet so i used the ffmpeg to create the stream :

  ffmpeg -f alsa -i hw:0  -acodec libmp3lame -f rtp rtp://224.1.2.4:7001/test.ffm

  The streaming is working perfectly between 2 computers in the same lanso i tried this code to get the audio streaming working on tablet but i hear nothing coming out from the tablet . note that 192.168.1.120 is my tablet’s ip .

   try {
  
                      audioGroup = new AudioGroup();
  
                      audioGroup.setMode(AudioGroup.MODE_NORMAL);
  
                      audioStream = new AudioStream(InetAddress.getByAddress(new byte[] {(byte)192, (byte)168, (byte)1, (byte)120 }));
  
                      audioStream.setCodec(AudioCodec.PCMU);
  
                      audioStream.setMode(RtpStream.MODE_NORMAL);
  
                      audioStream.associate(InetAddress.getByAddress(new byte[] {(byte)224, (byte)1, (byte)2, (byte)4 }), 7001);
  
                     audioStream.join(audioGroup);
  
                     AudioManager Audio =  (AudioManager) getSystemService(Context.AUDIO_SERVICE);
  
                      Audio.setMode(AudioManager.MODE_IN_COMMUNICATION);
  
                  }
  
                  catch (SocketException e) { e.printStackTrace();}
  
                  catch (UnknownHostException e) { e.printStackTrace();}
  
                  catch (Exception ex) { ex.printStackTrace();}}

  Please i need to know what’s the problem and how to fix it .

• FFMPEG - Make fragmented MP4 video start at 5 seconds (start time 00:05 instead of 00:00)

  17 mars 2021, par danielbernatek

  I am developing a live video streaming website (webinars), using MSE. I have almost done - everything in the whole process is working perfectly, except this :

  


  Data coming from the streamer in 5 second intervals are appended to the one WEBM file. Then I push this file into FFMPEG like this :

  


  ffmpeg -n -ss SEGMENT_I_WANT_START_TIME -to SEGMENT_I_WANT_END_TIME -i INPUT_WEBM_FILE -preset veryfast -max_muxing_queue_size 9999 -crf 30 -vf \"fps=15\" -copyts OUTPUT_MP4_SEGMENT


  


  The example above works perfectly, but output is not fragmented so it is not playable in MSE.

  


  When I add this : -movflags empty_moov+default_base_moof+frag_keyframe , the output is properly fragmented and playable in MSE but -copyts is not working, so my fragment starts at 0:00 instead of, for example, 0:05. This is making it unable for me to use SEGMENTS mode in MSE (because all segments sent to the client are appended to 0:00) and have to use the SEQUENCE mode, which is causing AV sync issues.

  


  I have also tried -output_ts_offset but with the same result - when used without fragmentation flag it is working well, but with it, it is not working at all. Looks like fragmented MP4 needs to start at 0:00 which I guess is not true.

  


  So the question is HOW TO USE -COPYTS OR -OUTPUT_TS_OFFSET WITH -MOVFLAGS ? Expected result is properly fragmented MP4 video segment which is playable using MSE and starts at not null time.

  


  Many thanks for any advice, I am fighting with this for days !