Recherche avancée

Sur d’autres sites (10889)

• How to identify exact type or variation of a .mp4 file

  5 octobre 2017, par Dave502619

  Can anyone tell me if there are different variations of mp4 file and if so, how to identify the exact type or variation of a mp4 file ?

  The reason I need to know this is if I pass an .mp4 through FFMPEG to create an uncompressed grayscale rgb24 avi file, depending on
  where the .mp4 file has been sourced from will produce a different internally structured avi file as output from FFMPEG. Ie, the file header
  and interframe header sizes differ.

  The ffmpeg command i am using is :
  ffmpeg.exe -i source.mp4 -b 1150 -r 20.97 -g 120 -an -vf format=gray -f rawvideo -pixfmt rgb24 -s 384x216 -vcode rawvideo -y fileX.avi

  So far I have identified that .mp4 files generated by my Samsung S5 mobile phone differ from .mp4 files generated by Power Director 14. So I suspect there are different variations of .mp4 files.

  I have written some software which steps into the FFMPEG output .avi file to extract video frames, but it requires fixed offset positions to work so I can only make it work for one variation of .mp4.

• Pass individual frames as BGRA byte array and set the timestamps via pipe to FFmpeg

  30 juillet 2023, par Nicke Manarin

  I have a set of images (as BGRA byte[]) with their respective timestamps in milliseconds and I want to pass it to FFmpeg to build an animation.

  


  I'm using FFmpeg v6 right now and in this example I'm expecting a GIF as output, but I'm going to export to multiple formats later.

  


  var arguments = "-vsync passthrough  
-f rawvideo 
-pix_fmt bgra 
-video_size {width}x{height} 
-i -  
-loop 0 
-lavfi palettegen=stats_mode=diff[pal],[0:v][pal]paletteuse=new=1:dither=sierra2_4a:diff_mode=rectangle 
-f gif 
-y \"C:\Users\User\Desktop\test.gif\"";

var process = new Process
{
    StartInfo = new ProcessStartInfo
    {
        FileName = "./ffmpeg.exe",
        Arguments = arguments.Replace("{width}", width.ToString()).Replace("{height}", height.ToString()),
        RedirectStandardInput = true,
        RedirectStandardOutput = true,
        UseShellExecute = false,
        CreateNoWindow = true
    }
};

_process.Start();



  


  Then on my render loop, I'm trying to send the frames and their timestamps one by one.

  


  public void EncodeFrame(IntPtr bufferAddress, int bufferStride, int width, int height, int index, long timestamp, int delay)
{
    var frameSize = height * bufferStride;
    var frameBytes = new byte[frameSize];
    System.Runtime.InteropServices.Marshal.Copy(bufferAddress, frameBytes, 0, frameSize);

    _process.StandardInput.BaseStream.Write(frameBytes, 0, frameSize);
    _process.StandardInput.BaseStream.Write(_delimiter, 0, _delimiter.Length);
    _process.StandardInput.BaseStream.Write(BitConverter.GetBytes(timestamp), 0, sizeof(long));
}


  


  The issue is that I'm getting an IOException (The pipe has been ended), so probably I'm not sending the frames correctly (not sending the delimiter and timestamp doesn't help).

  


  Is this even possible ?

  


• Setting individual pixels of an RGB frame for ffmpeg encoding

  15 mai 2013, par Camille Goudeseune

  I'm trying to change the test pattern of an ffmpeg streamer, Trouble syncing libavformat/ffmpeg with x264 and RTP , into familiar RGB format. My broader goal is to compute frames of a streamed video on the fly.

  So I replaced its AV_PIX_FMT_MONOWHITE with AV_PIX_FMT_RGB24, which is "packed RGB 8:8:8, 24bpp, RGBRGB..." according to http://libav.org/doxygen/master/pixfmt_8h.html .

  To stuff its pixel array called data, I've tried many variations on

  for (int y=0; y/  const double j = y/double(HEIGHT);
  
      rgb[0] = 255*i;
  
      rgb[1] = 0;
  
      rgb[2] = 255*(1-i);
  
    }
  
  }

  At HEIGHTxWIDTH= 80x60, this version yields
  , when I expect a single blue-to-red horizontal gradient.

  640x480 yields the same 4-column pattern, but with far more horizontal stripes.

  640x640, 160x160, etc, yield three columns, cyan-ish / magenta-ish / yellow-ish, with the same kind of horizontal stripiness.

  Vertical gradients behave even more weirdly.

  Appearance was unaffected by an AV_PIX_FMT_RGBA attempt (4 not 3 bytes per pixel, alpha=255). Also unaffected by a port from C to C++.

  The argument srcStrides passed to sws_scale() is a length-1 array, containing the single int HEIGHT.

  Access each Pixel of AVFrame asks the same question in less detail, so far unanswered.

  The streamer emits one warning, which I doubt affects appearance :

  [rtp @ 0x269c0a0] Encoder did not produce proper pts, making some up.

  So. How do you set the RGB value of a pixel in a frame to be sent to sws_scale() (and then to x264_encoder_encode() and av_interleaved_write_frame()) ?