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• avformat/hlsenc : Add resend_headers option

  27 juin 2022, par huheng

  avformat/hlsenc : Add resend_headers option
  Add pat and pmt table at start of each segment in single_file mode enhanced
  
  compatibility of hls stream. Because some hls clients separate parsing segment
  
  of hls stream, the absence of pat/pmt will cause parsing to fail.
  Reviewed-by : Steven Liu <liuqi05@kuaishou.com>
  
  Signed-off-by : huheng <heng.hu.1989@gmail.com>
  

  • [DH] libavformat/hlsenc.c

• What is this initial delay when using FFmpeg ?

  9 juin 2022, par massivemoisture

  I have a C# application that receives H264 stream through a socket. I want to continuously get the latest image from that stream as a byte array.

  


  Here's how I start ffmpeg.

  


  var ffmpegInfo = new ProcessStartInfo(FFMPEG_PATH);
ffmpegInfo.RedirectStandardInput = true;
ffmpegInfo.RedirectStandardOutput = true;
ffmpegInfo.RedirectStandardError = true;
ffmpegInfo.UseShellExecute = false;
ffmpegInfo.CreateNoWindow = true;

ffmpegInfo.Arguments = "-i pipe: -f rawvideo -pix_fmt bgr24 -an -sn pipe:"; 
Process myFFmpeg = new Process();
myFFmpeg.StartInfo = ffmpegInfo;
myFFmpeg.EnableRaisingEvents = true;

myFFmpeg.Start();
var inStream = myFFmpeg.StandardInput.BaseStream;
FileStream baseStream = myFFmpeg.StandardOutput.BaseStream as FileStream;
myFFmpeg.BeginErrorReadLine();


  


  Then I put the method receiving the stream in a ThreadPool thread. In this method, I put a Console.WriteLine to see how many bytes I get from socket for each Receive() method. I will call this the receive part.

  


  // inStream is the "var inStream = myFFmpeg.StandardInput.BaseStream;" from the block above
// var len = mySocket.Receive(receiveBuffer); receiveBuffer is a byte array with size of 65535
var t = Task.Run(() => ReceiveVideoStream(inStream));


  


  Lastly, I read the output from FFmpeg in a while loop. I will call this the read part.

  


  int frameCount = 0;

int BufferSize = Width * Height * 3;
decoded = new byte[BufferSize];

int numBytesToRead = BufferSize;
int numBytesRead = 0;

while (true)
{
   while (numBytesToRead > 0)
   {
      int n = baseStream.Read(decoded, numBytesRead, numBytesToRead);
      Console.WriteLine($"Read {n} bytes from ffmpeg, remaining = {numBytesToRead - n}");
      if (n == 0)
      {
         break;
      }
      numBytesRead += n;
      numBytesToRead -= n;
   }
   numBytesRead = 0;
   numBytesToRead = BufferSize;

   frameCount++;
   Console.WriteLine($"--- Received {frameCount} frames");
}


  


  With the receive part in a separate thread from the read part, I expected that the two parts would run in parallel, the debug messages that I put in those two parts will show up in between each other. But I notice that in the beginning, the read part is not executed (it seems that the Read method call blocks, if so, why does it block at this time ?), the receive part will receive for an X amount of bytes, then FFmpeg shows this log :

  


  Input #0, h264, from 'pipe:':
Duration: N/A, bitrate: N/A
Stream #0:0: Video: h264 (Baseline), yuv420p(progressive), 1280x720, 25 fps, 25 tbr, 1200k tbn, 50 tbc
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> rawvideo (native))
Output #0, rawvideo, to 'pipe:':
Metadata:
encoder : Lavf58.45.100
Stream #0:0: Video: rawvideo (BGR[24] / 0x18524742), bgr24, 1280x720, q=2-31, 552960 kb/s, 25 fps, 25 tbn, 25 tbc
Metadata:
encoder : Lavc58.91.100 rawvideo


  


  now the receive part and the read part run over each other.

  


  And if the source H264 video frames do not have movement, after several runs, I find that these X bytes are constant.

  


  I want to know what those first X amount of bytes are. And can I change it ?

  


• FFMpeg : 2 pass encoding, first with CRF and second with maxrate of first pass average bitrate ?

  28 septembre 2022, par Alireza Rinan

  I usually do conversions with ffmpeg 1 pass CRF 22 with maxrate 1400k for some movies to convert them to 720p and generate smallest size with best quality, the parameters I use is :

  


  c:v libx264 -vf format=yuv420p,scale=1280:-2 -crf 22 -maxrate 1400k -bufsize 7000k


  


  Doing this too much I found that apart from the black bars that reduces bitrate, the color theme, number of high movement scenes... etc affects the bitrate too much, CRF 22 makes sure you get constant quality at every scene, that makes bitrate reaches my maximum 1400k at some scenes while the reset of the scenes in some movies are barely 800k, this result the average bitrate for a same movie reaches for example about 1100k, for these movies I do the encoding again with lower maxrate
(Ex:1100k) and I get same quality with lower average rate 1000k.

  


  Now I'm wondering is there any automated method in 2 pass to get same result ?
For example doing the first pass in CRF 22 and the second pass at average bitrate of first pass to lower the quality of those bitrate rages in first pass ?