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• 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

• 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...

• Merge commit ’5a0e953c2465be9d449d5f523c3d3e2b886910b2’

  13 mars 2015, par Michael Niedermayer

  Merge commit ’5a0e953c2465be9d449d5f523c3d3e2b886910b2’
  * commit ’5a0e953c2465be9d449d5f523c3d3e2b886910b2’ :
  
    mjpeg : Mark decoder family as thread safe
  Conflicts :
  
  	libavcodec/mjpegbdec.c
  
  	libavcodec/mjpegdec.c
  
  	libavcodec/mxpegdec.c
  
  	libavcodec/sp5xdec.c
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/jpeglsdec.c
  • [DH] libavcodec/mjpegbdec.c
  • [DH] libavcodec/mjpegdec.c
  • [DH] libavcodec/mxpegdec.c
  • [DH] libavcodec/sp5xdec.c