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• ffmpeg in:h264 out:yuv to stdout - data format ?

  27 février 2019, par Petr

  I am (like many) trying to get a continuous series of still images out of the camera attached to a raspberry pi. I want to do this in java for all the usual reasons, and am using a Runtime exec command to pipe the output of raspivid to the following ffmpeg command, and then collecting the result via stdout --- note xxx.h264 is a test file generated by the camera that does not play because there is no container, but I am getting images out so half good.

  ffmpeg -i xxx.h264 -vcodec rawvideo -r 2 -pix_fmt yuv420p -f nut -

  I have some code displaying the frames, but they "march" across the display area from left to right, and there appears to be a growing amount of rubbish across the top of the images. I have looked at the bytes it outputs by running the same command and redirecting it into a file, then using vi/xxd and find that there is headder material ("nut/multimedia container ...").

  I am guessing that there is more metadata inserted by my ffmpeg command, that I am failing to remove when processing the raw yuv420p data as described here : https://en.wikipedia.org/wiki/YUV#Y%E2%80%B2UV420sp_%28NV21%29_to_RGB_conversion_%28Android%29

  For the life of me I cannot find the nut documentation anywhere in a readable format and anyway, it seems that is not what I should be looking for. Any pointers as to how I can recognise the frame boundaries in my byte stream ?

• FFmpeg check channels of a 7.1 audio for silence

  24 septembre 2019, par Tina J

  This is a follow-up question from my previous question asked here, where I needed to look for silence within a specific audio track. Here is the ffmpeg life-saver solution where helps to get some metadata :

  ffmpeg -i file -map 0:a:1 -af astats -f null -

  But I have other type of input .mp4 files where they have one single track of 8 (i.e. 7.1) audio channels. Apparently these files are transcoded from an original file (somehow the 4 track stereos are squished into these files). Now similar to my previous, I need to know if the original file was 2-channel stereo or 5.1 (6) channel.

  How to know if a specific channel of an audio track (say Center channel) is silent/mute, possibly using ffmpeg ? Here is a sample .mp4 file.

• Can VideoView be detach and reattached without stopping the stream ?

  17 septembre 2018, par Thierry-Dimitri Roy

  I’m building an app where the user clicks on a button to show a video full screen. Initially the video is attached to a view inside a ViewPager. To be able to show it fullscreen I detach it from its parent and reattach it to the root view. This works fine, except when the video is switched to fullscreen while playing. When I detach a playing VideoView it just stop and I need to restart it. This is not acceptable since the video starts buffering before resume. Here the part of the code where the detach is done :

      final ViewGroup parent = (ViewGroup) findViewById(R.id.parent);
  
  
  
      final ViewGroup root = (ViewGroup) findViewById(R.id.root);
  
  
  
      Button b = (Button) findViewById(R.id.button);
  
      b.setOnClickListener(new OnClickListener() {
  
  
  
          @Override
  
          public void onClick(View v) {
  
              parent.removeView(mVideoView);
  
  
  
              LayoutParams lp = new FrameLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
  
              root.addView(mVideoView, lp);
  
          }
  
      });

  Depending of the device, I have a different log error. Probably because the actual video player is provided by the manufacturer and not the Android SDK. Here are the error logs for a Nexus 7 :

  10-30 20:26:18.618: D/NvOsDebugPrintf(124): NvMMDecTVMRDestroyParser Begin 
  
  10-30 20:26:18.618: D/NvOsDebugPrintf(124): --------- Closing TVMR Frame Delivery Thread -------------
  
  10-30 20:26:18.678: D/NvOsDebugPrintf(124): ------- NvAvpClose -------
  
  10-30 20:26:18.678: D/NvOsDebugPrintf(124): NvMMDecTVMRDestroyParser Done 
  
  10-30 20:26:18.678: D/NvOsDebugPrintf(124): NvMMLiteTVMRDecPrivateClose Done 

  I haven’t been able to detach the video without stopping it. I tried using SurfaceView or TextureView without success.

  I also tried finding a third party video player. I found a commercial one (http://www.vitamio.org/) that I can’t really use for business reason. I found an open source one, that hasn’t been updated in the last year (https://code.google.com/p/dolphin-player/).

  I’m currently targeting Android 4.2 or better on tablet only.

  ---

  Note that the ViewPager is not fullscreen. So I can’t use LayoutParams to make the video fullscreen. I need to remove the VideoView from the parent in the ViewPager and add it to the root view to be able to show it fullscreen.

  The URL I’m testing with : http://bellvps1.cpl.delvenetworks.com/media/e1b3e24ecb944abd8f4ed823a0b76ddc/68f78d35296243bfb46d2418f03f2fd0/bande-annonce---the-secret-life-of-walter-mitty-1-9efcc5c6e52ac07a3edf84a1b21967995b7796a2.m3u8