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• avcodec/pngdec : Fix APNG_DISPOSE_OP_BACKGROUND

  20 août 2022, par Andreas Rheinhardt

  avcodec/pngdec : Fix APNG_DISPOSE_OP_BACKGROUND
  APNG works with a single reference frame and an output frame.
  
  According to the spec, decoding APNG works by decoding
  
  the current IDAT/fdAT chunks (which decodes to a rectangular
  
  subregion of the whole image region), followed by either
  
  overwriting the region of the output frame with the newly
  
  decoded data or by blending the newly decoded data with
  
  the data from the reference frame onto the current subregion
  
  of the output frame. The remainder of the output frame
  
  is just copied from the reference frame.
  
  Then the reference frame might be left untouched
  
  (APNG_DISPOSE_OP_PREVIOUS), it might be replaced by the output
  
  frame (APNG_DISPOSE_OP_NONE) or the rectangular subregion
  
  corresponding to the just decoded frame has to be reset
  
  to black (APNG_DISPOSE_OP_BACKGROUND).
  The latter case is not handled correctly by our decoder :
  
  It only performs resetting the rectangle in the reference frame
  
  when decoding the next frame ; and since commit
  
  b593abda6c642cb0c3959752dd235c2faf66837f it does not reset
  
  the reference frame permanently, but only temporarily (i.e.
  
  it only affects decoding the frame after the frame with
  
  APNG_DISPOSE_OP_BACKGROUND). This is a problem if the
  
  frame after the APNG_DISPOSE_OP_BACKGROUND frame uses
  
  APNG_DISPOSE_OP_PREVIOUS, because then the frame after
  
  the APNG_DISPOSE_OP_PREVIOUS frame has an incorrect reference
  
  frame. (If it is not followed by an APNG_DISPOSE_OP_PREVIOUS
  
  frame, the decoder only keeps a reference to the output frame,
  
  which is ok.)
  This commit fixes this by being much closer to the spec
  
  than the earlier code : Resetting the background is no longer
  
  postponed until the next frame ; instead it is applied to
  
  the reference frame.
  Fixes ticket #9602.
  (For multithreaded decoding it was actually already broken
  
  since commit 5663301560d77486c7f7c03c1aa5f542fab23c24.)
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/pngdec.c

• Audio and video out of sync. Stream mp4 files Concatenation using fluent-ffmpeg

  13 mars 2021, par JosepB

  First of all sorry if the question is duplicated. But I couldn't find out the right answer in other questions.

  


  I'm trying to concatenate AWS S3 mp4 files using streams and fluent-ffmpeg. I managed to download and upload the concatenated files without storing it to the disk.

  


  The concatenation seems correct but when I'm selecting a point in time of the video player (VLC media player or QuickTime) time bar seems the audio and video are out of sync.

  


  This is the nodejs fluent-ffmpeg implementation :

  


  concatenation = (listFileName, passthroughStream) => {

    return new Promise((resolve) => {  
        let command = ffmpeg().input(listFileName)
            .inputOptions(['-f concat', '-safe 0', '-protocol_whitelist', 'file,http,tcp,https,tls'])
            //.videoCodec('libx264')
            .outputFormat('mp4')
            .outputOptions('-movflags frag_keyframe+empty_moov')
            
            var ffstream = command.on('end', function() {
                const result = 'files have been merged succesfully';
                resolve(result);
            })
            .on('error', function(err) {
                console.log('an error happened: ' + err.message);
                reject(err);
            }).pipe(passthroughStream);
            ffstream.on('data', ((chunk) => {
                console.log('ffmpeg just wrote ' + chunk.length + ' bytes');
            }));
    });        
}


  


  I'm using S3 file signed URLs in the file. Somthing like this :

  


  file 'https://bucket.s3.region.amazonaws.com/file_0.mp4'
file 'https://bucket.s3.region.amazonaws.com/file_1.mp4'


  


  I think that this out of sync is because of the fragmentated output and maybe is not possible to do that without downloading the files, but maybe there's a possible solution.

  


  Is there some way to do the mp4 concatenation without storing the files to the disk ? Or am I doing something wrong ?

  


• how to crop the video with ffmpeg . needed c api to do same

  9 avril 2016, par OpenSource

  I want to crop the video at particular portion.Given height,width,x and y ,I want crop the particular region on the video with help of ffmpeg in iOS.
  any help