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• How to decode in C a stream from this noname almost-UVC grayscale camera

  18 janvier 2019, par scriptfoo

  Edit : I found the cause. The stream always begins with something which is not a JPEG. Only after it there is a normal MJPEG stream. Interestingly, not all of the small examples of using V4L2/MJPEG decoders can divide what the camera produces properly into frames. Something called capturev4l2.c is a rare example of doing it properly. Possibly there is some detail, which decides if the camera’s bugginess is worked around or not.

  I have a noname almost-UVC-compliant camera (it fails several compatibility tests). This is a relatively cheap global shutter camera, and thus I would like to use it instead of something properly documented. It outputs what is reported (and properly played) by mplayer as

  Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
  
  libavcodec version 57.107.100 (external)
  
  Selected video codec: [ffmjpeg] vfm: ffmpeg (FFmpeg MJPEG)

  ffprobe shows the following :

  [mjpeg @ 0x55c086dcc080] Format mjpeg detected only with low score of 25, misdetection possible!
  
  Input #0, mjpeg, from '/home/sc/Desktop/a.raw':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: mjpeg, yuvj422p(pc, bt470bg/unknown/unknown), 640x480, 25 tbr, 1200k tbn, 25 tbc

  But as opposed to mplayer, it is unable to play it.

  I tried decode_jpeg_raw from mjpegtools, it complains about the header, which seems to change with each captured stream. So does not look like an unwrapped stream of JPEG images.

  I thus tried 0_hello_world.c from libavcodec/libavformat, but its stops at avformat_open_input() with an error Invalid data found when processing input. A 100-frame sample file is sitting here a.raw. Do you have any idea how to determine a method of decoding it in C into anything plain bitmap ?

  The file is grayscale, does not begin with a constant value, guvcview and mplayer are the only players I know, which can decode it without artifacts...

• avutil/frame : add AV_SIDE_DATA_PROP_{SIZE,COLOR}_DEPENDENT

  4 décembre 2024, par Niklas Haas

  avutil/frame : add AV_SIDE_DATA_PROP_SIZE,COLOR_DEPENDENT
  Many filters modify certain aspects of frame data, e.g. through resizing
  
  (vf_*scale* family), color volume mapping (vf_lut*, vf_tonemap*), or
  
  possibly others.
  When this happens, we should strip all frame side data that will no
  
  longer be correct/relevant after the operation. For example, changing
  
  the image size should invalidate AV_FRAME_DATA_PANSCAN because the crop
  
  window (given in pixels) no longer corresponds to the actual image size.
  
  For another example, tone-mapping filters (e.g. from HDR to SDR) should
  
  strip all of the dynamic HDR related metadata.
  Since there are a lot of different side data types that are affected by such
  
  operations, it makes sense to establish this information in a common, easily
  
  accessible way. The existing side data properties enum is a perfect fit for
  
  this.
  

  • [DH] doc/APIchanges
  • [DH] libavutil/frame.c
  • [DH] libavutil/frame.h
  • [DH] libavutil/version.h

• What is the "Error initializing filter 'drawtext' with args..." error in using of ffmpeg at c# process class ?

  7 novembre 2016, par parsa

  I used this below code for create a resolution of a video and write text on it.

      var proc = new System.Diagnostics.Process();
  
      strin OrginalResolution="nhd";
  
      proc.EnableRaisingEvents = false;
  
      proc.StartInfo.FileName = ffmpegPath;
  
      proc.StartInfo.Arguments = "-i \"" + fileIn +
  
                                 "\" -f mp4 -s " + OrginalResolution + " -vf drawtext=fontfile=/OtherProjects/ConvertProj/ff‌​mpeg/OpenSans-Reg‌​ular.ttf:text=Parsa" \"" + fileOut.Split('.')[0] +
  
                                 ".mp4";
  
      proc.StartInfo.UseShellExecute = false;
  
      proc.StartInfo.CreateNoWindow = false;
  
      proc.StartInfo.RedirectStandardOutput = true;
  
      proc.StartInfo.RedirectStandardError = true;
  
  
  
      proc.Start();
  
      proc.WaitForExit();
  
      string sdsd = proc.StandardError.ReadToEnd();
  
      proc.Close();

  I faced with this problem(some string output of StandardError is in below) :

  Fontconfig error: Cannot load default config file\r\n[Parsed_drawtext_0       
  
  @0000000002fd8c20] Cannot find a valid font for the family 
  
  Sans\r\n[AVFilterGraph @ 0000000000511660] Error initializing 
  
  filter'drawtext' with args 
  
  'fontfile=/OtherProjects/ConvertProj/ffmpeg/OpenSans-
  
  Regular.ttf:text=parsa'\r\nError opening 
  
  filters!\r\n

  In cmd the same argument value of process works fine.
  I read that this issue related to how to using quotation mark at using
  of text property of drawtext in ffmpeg.but I can’t find any
  solution for solving this issue.
  Can anyone help me ?

  Can anyone help me still ?Is this a bug ?
  I used any solutions for escape from : in my code,but can’t solve this problem.
  It can’t find font.I delete other filters of drawtext to findout that any of filters don’t mistake, but still error exists yet.

  expansion=none property of drawtext doesn’t influence on this case, for escape :.