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• How to download a part of mp3 from server ?

  20 août 2020, par Sharukh Mohammed

  Use Case

  


  My use case is roughly equal to, adding a 15-second mp3 file to a 1 min video. All transcoding merging part will be done by FFmpeg-android so that's not the concern right now.

  


  The flow is as follows

  


  

  • User can select any 15 seconds (ExoPlayer-streaming) of an mp3 (considering 192Kbps/44.1KHz of 3mins = up to 7MB)

  


  • Then download ONLY the 15 second part and add it to the video's audio stream. (using FFmpeg)

  


  • Use the obtained output

  


  


  Tried solutions

  


  


  • Extracting fragment of audio from a url

    


    RANGE_REQUEST - I have replicated the exact same algorithm/formula in Kotlin using the exact sample file provided. But the output is not accurate (± 1.5 secs * c) where c is proportional to startTime

    


  


  • How to crop a mp3 from x to x+n using ffmpeg ?

    


    FFMPEG_SS - This works flawlessly with remote URLs as input, but there are two downsides,

    


    

    1. as startTime increases, the size of downloaded bytes are closer to the actual size of the mp3.

    


    2. ffmpeg-android does not support network requests module (at least the way we complied)

    


    


  


  


  So above two solutions have not been fruitful and currently, I am downloading the whole file and trimming it locally, which is definitely a bad UX.
I wonder how Instagram's music addition to story feature works because that's close to what I wanted to implement.

  


• FFMpeg, libav, Problem with sws_scale and yuv to rgb conversion - colors are not correct

  7 juillet 2022, par Milika

  I've been trying to create my own video player in Delphi, and ffmpeg works great, until i hit a snag with color spaces, or color conversion.

  


  Been trying everything for a couple of days, but can't figure it out.
I'm using AV_PIX_FMT_RGB48LE as output...

  


  Old context creation :

  


        videoConvContext := sws_getContext(AVStreamInit.codec.width, AVStreamInit.codec.height, AVStreamInit.codec.pix_fmt, AVStreamInit.codec.width, AVStreamInit.codec.height, AV_PIX_FMT_RGB48LE, SWS_POINT, nil, nil, nil);


  


  New context creation :

  


      dstRange := 1;
    srcRange := 1;
    if AVStreamInit.codec.color_range = AVCOL_RANGE_MPEG then
      srcRange := 0;

    videoConvContext := sws_alloc_context();

    av_opt_set_int(videoConvContext, 'sws_flags', SWS_POINT or SWS_PRINT_INFO, 0);

    av_opt_set_int(videoConvContext, 'srcw', AVStreamInit.codec.width, 0);
    av_opt_set_int(videoConvContext, 'srch', AVStreamInit.codec.height, 0);
    av_opt_set_int(videoConvContext, 'src_format', Integer(AVStreamInit.codec.pix_fmt), 0);

    av_opt_set_int(videoConvContext, 'dstw', AVStreamInit.codec.width, 0);
    av_opt_set_int(videoConvContext, 'dsth', AVStreamInit.codec.height, 0);
    av_opt_set_int(videoConvContext, 'dst_format', Integer(AV_PIX_FMT_RGB48LE), 0);

    i1 := sws_getCoefficients2(Integer(AVStreamInit.codec.colorspace));
    i2 := sws_getCoefficients2(SWS_CS_ITU709);

    ret := sws_setColorspaceDetails2(videoConvContext, i1, srcRange, i2, dstRange, 0, 1 shl 16, 1 shl 16);

    sws_init_context(videoConvContext, nil, nil);


  


  Results are exactly the same....

  


  Output from sws_scale does not have correct colors, here are 2 screenshot

  


  ok - from mpc-hc


  


  not ok - from my player via sws_scale (direct raw extract so no color processing done)


  


  This video has pix_fmt AV_PIX_FMT_YUV420P10LE, but it happens on other YUV inputs, but not so obvious. Also on other RGB outputs(8bit etc)...
Here the Netflix logo is pure red, but sws_scale output gives orange-ish...

  


  Sws_scale code just for reference :

  


  sws_scale(videoConvContext, @AVPacketBuffer.AVFrameCopy.Data, @AVPacketBuffer.AVFrameCopy.linesize, 0, AVStream.codec.height, @BitmapXBuffer.data, @linesize);


  


  BitmapXBuffer.data is a signle buffer of correct size...

  


  AVFrameCopy - is a copy of original frame done with :

  


    if Assigned(AVPacketBuffer.AVFrameCopy) then
      av_frame_free(@AVPacketBuffer.AVFrameCopy);

    AVPacketBuffer.AVFrameCopy := av_frame_alloc();
    AVPacketBuffer.AVFrameCopy.format := AVPacketBuffer.AVFrame.format;
    AVPacketBuffer.AVFrameCopy.width := AVPacketBuffer.AVFrame.width;
    AVPacketBuffer.AVFrameCopy.height := AVPacketBuffer.AVFrame.height;
    AVPacketBuffer.AVFrameCopy.channels := AVPacketBuffer.AVFrame.channels;
    AVPacketBuffer.AVFrameCopy.channel_layout := AVPacketBuffer.AVFrame.channel_layout;
    AVPacketBuffer.AVFrameCopy.nb_samples := AVPacketBuffer.AVFrame.nb_samples;
    av_frame_get_buffer(AVPacketBuffer.AVFrameCopy, 32);
    av_frame_copy(AVPacketBuffer.AVFrameCopy, AVPacketBuffer.AVFrame);
    av_frame_copy_props(AVPacketBuffer.AVFrameCopy, AVPacketBuffer.AVFrame);


  


  Thanks !

  


• FFmpeg : chromakey without green edges

  5 septembre 2020, par Igniter

  I have a video of a person on green background and I'm trying to turn background transparent by this :

  


  ffmpeg -i bg.mp4 -i man.mp4 -filter_complex '[1:v]colorkey=0x00ff00:0.3:0.3[ckout];[0:v][ckout]overlay[out]' -map '[out]' result.mp4


  


  Colorkey gives this quite noticeable green edge around the person's figure.
  
Any attempts to increase opacity or blend parameters result in disappearing facial features.

  


  

  


  Is there any smart way to change pure green 0x00ff00 pixels with transparent ones ?