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• Programmatically sending bytes to ffmpeg via STDIN to create still image file

  8 octobre 2019, par Sam Marrocco

  I am attempting to use vb.net code to send individual pixel information as bytes to ffmpeg with the purpose of saving a still DPX image file. I have already successfully read DPX files and output them via STDOUT into vb.net code.

  There seem to be many examples out there of piping movie files but there are also discrepancies, such as some people using image2pipe and others using rawvideo. I am uncertain when to use one over the other. The various methods I’ve tried result in ffmpeg returned errors such as "Packet too small for DPX header" or "Error while decoding stream #0:0 : Invalid data found when processing input". As I understand it, I am not providing a header, only the raw individual pixel RGBRGBRGB.... values as a byte array.

  The arguments sent to ffmpeg via command line are :

  -f image2pipe -pix_fmt rgb24 -s 16x16 -bits_per_raw_sample 8 -c:v dpx -i - \MyPath\MyFilename.dpx

  My vb.net code is as follows :

  Dim P As New Process
  
  P.StartInfo.FileName = m_FFMPEGExecutable_PathFile
  
  P.StartInfo.Arguments = (see above arguments)
  
  P.StartInfo.UseShellExecute = False
  
  P.StartInfo.CreateNoWindow = True
  
  P.StartInfo.RedirectStandardInput = True
  
  p.Start
  
  
  
  
  
  'Test image: A single red, green, blue, black and white pixel followed by all black
  
  
  
  Dim Tiny((16 * 16) - 1) As Byte
  
  
  
  Tiny(0) = 255
  
  Tiny(1) = 0
  
  Tiny(2) = 0
  
  
  
  Tiny(3) = 0
  
  Tiny(4) = 255
  
  Tiny(5) = 0
  
  
  
  Tiny(6) = 0
  
  Tiny(7) = 0
  
  Tiny(8) = 255
  
  
  
  For i As byte = 9 To ((16x16)-1)
  
     Tiny(i) = 255
  
  Next
  
  
  
  'Send the rgb byte array to ffmpeg:
  
  P.StandardInput.BaseStream.Write(Tiny, 0, Tiny.Length)
  
  P.StandardInput.Flush()
  
  P.StandardInput.Close()

  I have tried many variations on the above ffmpeg arguments but cannot seem to avoid these errors. Any suggestions would be appreciated, including information on when to use image2pipe vs. rawvideo.

• Changing x264 settings on the fly

  22 décembre 2018, par S Red

  I am curious to know if anyone has experience with modifying x264 settings during encoding (this is for testing live streaming hence I need to be able to modify settings based on cpu and upload characteristics).

  I saw an API for encoder_reconfig() in x264.h, curious if folks have used that, and if its accessible from ffmpeg ? Is it possible to modify a high-level option like ’preset’, or do I need to modify individual options like chroma-me, trellis etc.

• Changing x264 settings on the fly

  22 décembre 2018, par S Red

  I am curious to know if anyone has experience with modifying x264 settings during encoding (this is for testing live streaming hence I need to be able to modify settings based on cpu and upload characteristics).

  I saw an API for encoder_reconfig() in x264.h, curious if folks have used that, and if its accessible from ffmpeg ? Is it possible to modify a high-level option like ’preset’, or do I need to modify individual options like chroma-me, trellis etc.