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• How to extract MP4 seekpoints information from PHP/FFmpeg/MP4Box/Anything ?

  22 octobre 2014, par user3052587

  Is it possible to extract the seekpoints/keyframes from a MP4 file in the following fashion :

  Keyframe - Time Range (in seconds) - Offset (in bytes)

  Example :
  0 - 0s - 77262

  1 - 0.5s - 144183

  2 - 1s - 222965

  3 - 1.5s - 293303

  4 - 2s - 362199

  5 - 2.5s - 431178

  Thanks in advance.

• 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()) ?