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• JavaCV FFmpegFrameGrabber preload audio

  1er juillet 2015, par James

  I have an application that streams video data to a RTMP server using javacv’s FFmpegFrameRecorder. I want to add some audio to this stream from a separate file - a short sound clip that I want to play on repeat.

  Given the sound clip is very short, I want to preload the audio data into memory and just loop over it - so I can avoid excessive IO etc.

  I’ve attempted to add audio to the stream using javacv’s FFmpegFrameGrabber, as prescribed on multiple tutorials.

  The addition of audio works perfectly if I don’t attempt to preload/cache any of the audio data, for example :

  private FFmpegFrameRecorder frameRecorder;
  
  private FFmpegFrameGrabber frameGrabber;
  
  
  
  ...
  
  //frameRecorder and frameGrabber setup during initialization
  
  ...
  
  
  
  public void record(IplImage image) {
  
          try {
  
              frameRecorder.record(image);
  
              Frame frame = frameGrabber.grabFrame();
  
              if(frame == null) {
  
                  frameGrabber = new FFmpegFrameGrabber("audioFileHere.wav");
  
                  frameGrabber.start();
  
                  frame = frameGrabber.grabFrame();
  
              }
  
              frameRecorder.record(frame);
  
          } catch (FrameRecorder.Exception e) {
  
              log.error(getMarker(FATAL), "Can't record frame!", e);
  
          } catch (FrameGrabber.Exception e) {
  
              log.error(getMarker(FATAL), "Can't record frame!", e);
  
          }
  
  }

  However, if I try to preload the audio data I get garbage sound being played :

  private FFmpegFrameRecorder frameRecorder;
  
  private List<framedata> audioData;
  
  
  
  private static final class FrameData {
  
      public final Buffer[] samples;
  
      public final Integer sampleRate;
  
      public final Integer audioChannels;
  
  
  
      //Constructors, getters and setters here
  
  }
  
  
  
  ...
  
      //frameRecorder setup during initialization
  
      audioData = new ArrayList&lt;>();
  
      FFmpegFrameGrabber audioGrabber = new FFmpegFrameGrabber("audioFileHere.wav");
  
      try {
  
          audioGrabber.start();
  
          Frame frame;
  
          while ((frame = audioGrabber.grabFrame()) != null) {
  
              Buffer[] buffers = frame.samples;
  
              Buffer[] copiedBuffers = new Buffer[buffers.length];
  
              for (int i = 0; i &lt; buffers.length; i++) {
  
                  copiedBuffers[i] = ((ShortBuffer) buffers[i]).duplicate();
  
              }
  
              FrameData frameData = new FrameData(copiedBuffers, frame.sampleRate, frame.audioChannels);
  
              audioData.add(frameData);
  
          }
  
      } catch (FrameGrabber.Exception e) {
  
          e.printStackTrace();
  
      }
  
  ...
  
  
  
  private int frameCount = 0;
  
  
  
  public void record(IplImage image) {
  
      frameCount++;
  
      try {
  
          FrameData frameData = audioData.get(frameCount % audioData.size());
  
          frameRecorder.record(image);
  
          frameRecorder.record(frameData.sampleRate, frameData.audioChannels, frameData.samples);
  
      } catch (FrameRecorder.Exception e) {
  
          log.error(getMarker(FATAL), "Can't record frame!", e);
  
      }
  
  }
  
  </framedata>

  NOTE : I have to deep copy the Frame object because FFmpegFrameGrabber.grabFrame() recycles a single Frame object

  Can someone explain why this doesn’t work and/or how I could achieve the desired result ?

• Create video with size based on image and place a video somewhere with an offset

  10 mars 2024, par NoKey

  I am trying out FFMPEG and I am unsure how hard it is to do what I want. I have some device frames and I want to play a video inside the frame. For example, this is a device frame :

  


  

  


  Now I want to play a video within the screen of the iPhone. I already got the exact X and Y offset where the video must be placed to show it correctly. I have the following challenges to make it work, and I want to make sure FFMPEG can do it before I spend to much time reinventing the wheel :

  


  


  • The output of the video must be as big as the PNG. This is already a
confusing part for me. I have the width and height already available,
but the things I saw is that FFMPEG will take over the input of the
video as final size. The final output of the video should of course
be the length of the input video.

    


  


  • The background must be transparant (so no black background, I want to
play the video on top of a website so it's nice if it's transparant and the corners are not black).

    


  


  • The ability to place a video somewhere with a specified X and Y
offset inside the device frame.

    


  


  • Not sure if it's possible in the same command, but maybe the video
needs to be resized to make it fit. I got the exact dimensions for
the video.

    


  


  


  The things I struggle most is point 1 where the output video must have a transparant background and where the device frame is placed in. Does anybody got tips ?

  


• delay in lyrics shown when concat video with lyrics with an intro video using ffmpeg

  19 mars 2018, par no name

  I have a video with lyrics I add the lyrics used ffmpeg too. I have the lyrics in lrc formate and i change it to ass lyrics formate then I start to add it to my video using this command

  ffmpeg -i video.mp4 -vf "ass=out.ass,fade=in:0:30" -y amr.mp4

  I use fade=in:0:30 to make fade in the start of the video so when I start merge intro video my original video not start at once but to have some fade in, in the start to have a good view.
  then I start to add the intro video using a text file which has this

  file intro.mp4
  
  file amr.mp4

  then I merge them using this command

  ffmpeg -f concat -safe 0 -i out.txt -c copy -y final.mp4

  i got these message

  [mov,mp4,m4a,3gp,3g2,mj2 @ 03eadb80] Auto-inserting h264_mp4toannexb bitstream filter
  
  [mp4 @ 06419580] Non-monotonous DTS in output stream 0:1; previous: 310272,     current: 285626; changing to 310273. This may result in incorrect timestamps in   the output file.

  repeated many times.
  when i watch the final video the lyrics have some delay from the sound the problem appeared when I merge the intro video but without it the lyrics have no problem so what I made wrong make the lyrics shown in this way and not in the right timing as it should have no problems as I merge only the intro video and after add the lyrics to the original one
  Thanks in advance