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• Concatenating/Splicing overlapping video clips with ffmpeg

  16 décembre 2020, par Jimbo1987

  I'm trying to concatenate multiple short .mp4 video clips from a security camera. The camera records short clips, with a few seconds on either end of a timespan when motion is detected. For example, two minutes of video will often be broken up into four 35 second clips, with the first/last few seconds of each clip being duplicative of the last/first few seconds of the previous/next clip.

  


  I simply concatenate the clips together using the ffmpeg concat demuxer, as described here : How to concatenate two MP4 files using FFmpeg ?, with

  


  (echo file 'first file.mp4' & echo file 'second file.mp4' )>list.txt
ffmpeg -safe 0 -f concat -i list.txt -c copy output.mp4


  


  Or else I transcode them into intermediate MPEG-2 transport streams, which I can then concatenate with the file-level concat protocol, as described here : https://trac.ffmpeg.org/wiki/Concatenate#protocol, with

  


  ffmpeg -i "first file.mp4" -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts
ffmpeg -i "second file.mp4" -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts
ffmpeg -i "concat:intermediate1.ts|intermediate2.ts" -c copy -bsf:a aac_adtstoasc output.mp4


  


  But either way, the resulting video (output.mp4) jumps backward in time a few seconds every half-minute or so because of the duplicated frames.

  


  I want to throw out the duplicate frames, and tie the clips together based on timestamps to achieve smooth playback of the concatenated full-length video. I'd strongly prefer to do this on Windows with ffmpeg if possible. Surely this has been done before, right ? Are there timestamps in the .mp4 files that I can use to determine how much overlap there is, and then splice at the proper point-in-time ? And if so, how do I read them, how do I splice at an exact point in time, and how do I get around the KeyFrames issue if I can splice at the exact point in time ?

  


• Flutter record front facing camera at exact same time as playing video

  27 novembre 2020, par xceed

  I've been playing around with Flutter and trying to get it so I can record the front facing camera (using the camera plugin [https://pub.dev/packages/camera]) as well as playing a video to the user (using the video_player plugin [https://pub.dev/packages/video_player]).

  


  Next I use ffmpeg to horizontally stack the videos together. This all works fine but when I play back the final output there is a slight delay when listening to the audio. I'm calling Future.wait([cameraController.startVideoRecording(filePath), videoController.play()]); but there is a slight delay in these tasks actually starting. I don't even need them to fire at the exact same time (which I'm realising is probably impossible), instead if I knew exactly when each of the tasks begun then I can use the time difference to sync the audio using ffmpeg or similar.

  


  I've tried adding a listener on the videoController to see when isPlaying first returns true, and also watching the output directory for when the recorded video appears on the filesystem :

  


        listener = () {
        if (videoController.value.isPlaying) {
          isPlaying = DateTime.now().microsecondsSinceEpoch;
          log('isPlaying '+isPlaying.toString());
        }
        videoController.removeListener(listener);
      };
      videoController.addListener(listener);

      var watcher = DirectoryWatcher('${extDir.path}/');
      watcher.events.listen((event) {
        if (event.type == ChangeType.ADD) {
          fileAdded = DateTime.now().microsecondsSinceEpoch;
          log('added '+fileAdded.toString());
        }
      });


  


  Then likewise for checking if the camera is recording :

  


      var listener;
    listener = () {
      if (cameraController.value.isRecordingVideo) {
        log('isRecordingVideo '+DateTime.now().microsecondsSinceEpoch.toString());
        //cameraController.removeListener(listener);
      }
    };
    cameraController.addListener(listener);


  


  This results in (for example) the following order and microseconds for each event :

  


  is playing: 1606478994797247
is recording: 1606478995492889 (695642 microseconds later)
added: 1606478995839676 (346787 microseconds later)


  


  However, when I play back the video the syncing is off by approx 0.152 seconds so doesn't marry up to the time differences reported above.

  


  Does anyone have any idea how I could accomplish near perfect syncing when combining 2 videos ? Thanks.

  


• How do I know the time left in order to convert to an audio file, to use that to display the remainder for downloading in front of the user

  6 novembre 2020, par Kerols afifi

  I got this code from GITHUB, and this is better for me than using the FFmpeg library, because this library only works at a minimum. Issued 24 APIs, but the code that I got I don't know exactly how to tell me when the conversion is finished and also how much time is left because it's the conversion to appear. In front of the user

  


  @SuppressLint("NewApi")
    public void genVideoUsingMuxer(Context context,String srcPath, String dstPath, int startMs, int endMs, boolean useAudio, boolean useVideo,long time) throws IOException {
        // Set up MediaExtractor to read from the source.
         extractor = new MediaExtractor();
        extractor.setDataSource(srcPath);
        int trackCount = extractor.getTrackCount();
        // Set up MediaMuxer for the destination.

    mediaMuxer = new MediaMuxer(dstPath, MediaMuxer.OutputFormat.MUXER_OUTPUT_MPEG_4);
    // Set up the tracks and retrieve the max buffer size for selected
    // tracks.
    HashMap indexMap = new HashMap(trackCount);
    int bufferSize = -1;
    for (int i = 0; i < trackCount; i++) {
        MediaFormat format = extractor.getTrackFormat(i);
        String mime = format.getString(MediaFormat.KEY_MIME);
        boolean selectCurrentTrack = false;
        if (mime.startsWith("audio/") && useAudio) {
            selectCurrentTrack = true;
        } else if (mime.startsWith("video/") && useVideo) {
            selectCurrentTrack = true;
        }
        if (selectCurrentTrack) {
            extractor.selectTrack(i);
            int dstIndex = mediaMuxer.addTrack(format);
            indexMap.put(i, dstIndex);
            if (format.containsKey(MediaFormat.KEY_MAX_INPUT_SIZE)) {
                int newSize = format.getInteger(MediaFormat.KEY_MAX_INPUT_SIZE);
                bufferSize = newSize > bufferSize ? newSize : bufferSize;
            }
        }
    }
    if (bufferSize < 0) {
        bufferSize = DEFAULT_BUFFER_SIZE;
    }
    // Set up the orientation and starting time for extractor.
    MediaMetadataRetriever retrieverSrc = new MediaMetadataRetriever();
    retrieverSrc.setDataSource(srcPath);
    String degreesString = retrieverSrc.extractMetadata(MediaMetadataRetriever.METADATA_KEY_VIDEO_ROTATION);
    if (degreesString != null) {
        int degrees = Integer.parseInt(degreesString);
        if (degrees >= 0) {
            mediaMuxer.setOrientationHint(degrees);
        }
    }
    if (startMs > 0) {
        extractor.seekTo(startMs * 1000, MediaExtractor.SEEK_TO_CLOSEST_SYNC);
    }
    // Copy the samples from MediaExtractor to MediamediaMuxer. We will loop
    // for copying each sample and stop when we get to the end of the source
    // file or exceed the end time of the trimming.
    int offset = 0;
    int trackIndex = -1;
    time = bufferSize;
    ByteBuffer dstBuf = ByteBuffer.allocate(bufferSize);
    mediaMuxer.start();
    while (true) {
        bufferInfo.offset = offset;
        bufferInfo.size = extractor.readSampleData(dstBuf, offset);
        if (bufferInfo.size < 0) {
            Log.d(TAG, "Saw input EOS.");
            bufferInfo.size = 0;
            break;
        } else {
            bufferInfo.presentationTimeUs = extractor.getSampleTime();
            if (endMs > 0 && bufferInfo.presentationTimeUs > (endMs * 1000)) {
                Log.d(TAG, "The current sample is over the trim end time.");
                break;
            } else {
                bufferInfo.flags = extractor.getSampleFlags();
                trackIndex = extractor.getSampleTrackIndex();
                mediaMuxer.writeSampleData(indexMap.get(trackIndex), dstBuf, bufferInfo);
                extractor.advance();
            }
        }
    }

    mediaMuxer.stop();
    mediaMuxer.release();

    return;
}