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• vf_colorspace : Allow overriding input color properties

  3 septembre 2016, par Vittorio Giovara

  vf_colorspace : Allow overriding input color properties
  The filter needs input frames with color properties filled out by
  
  the decoder. Since this is not always possible, add input options to
  
  the filter so that user may override color space, color primaries,
  
  transfer characteristics, and color range, as well as a generic option
  
  to set all properties at once.
  Signed-off-by : Vittorio Giovara <vittorio.giovara@gmail.com>
  

  • [DH] doc/filters.texi
  • [DH] libavfilter/vf_colorspace.c

• How do I extract color matrix from MP4 an x264 stream in Media Foundation

  23 août 2016, par Jules

  I am playing a video (mp4 containing x264 encoded video stream) with a custom player using media foundation.

  When I convert the YUV information into RGB I need to account for the color matrix and range used at encode time.

  Some of my videos have this information, I can use MediaInfo.exe or FFMPEG to see that it is present.

  However, for such videos if I look at the relevant Media Foundation properties (Extended Color Information) the properties are not present in the files.

  So, somehow I need to find a way to access the information.

  Media Foundation does provide access to MF_MT_MPEG4_SAMPLE_DESCRIPTION and MF_MT_MPEG_SEQUENCE_HEADER for the video stream but I can’t find descriptions of what these contain.

  I noticed that the MF_MT_MPEG_SEQUENCE_HEADER is much longer for the videos with the information present and this (MPEG Headers Quick Reference) seems to suggest headers might contain the information I need.

  I’m looking for Color Range (limited/full), Color Primaries, Transfer Characteristics and Matrix Coefficients (BT.709 etc).

  I’d greatly appreciate any help finding this information from a Media Foundation video stream.

  Thanks

  Jules

  ---

  Update - Sequence Header

  The sequence header appears to be a subset of MPEG4 sample description, though I can’t find anything that indicates what either bits of data actually contains / doesn’t contain specifically.

  The sequence header appears to contain data structured as an MP4 byte stream as described in the H264 Standards Document and includes the VUI (Video Usability Information - Annex E of document) which may then include the colour information I’m interested in.

  Given that it’s a byte stream I need to know where it starts and whether there’s some existing code I could use to decode it.

  In FFMPEG in libavcodec/h264_ps.c there is a function called ff_h264_decode_seq_parameter_set which ends up calling decode_vui_parameters. It seems possible that seq_parameter_set maps to MF_MT_MPEG_SEQUENCE_HEADER and it may be possible to use that code to decode the data.

  If anyone one has any direct experience with decoding this data it would be very useful.

  Thanks again

  ---

  Update - Related posts

  I found this How to decode sprop-parameter-sets in a H264 SDP ? and Possible Locations for Sequence/Picture Parameter Set(s) for H.264 Stream which are fairly helpful.

  The sequence header would appear to be Sequence or picture parameter set (pps) and the parameters I want are the VUI extension subset.

  Plus this post H.264 stream structure gives the high level of how the stream data is structured, and the MF_MT_MPEG_SEQUENCE_HEADER appears to start with a NAL 0x00 0x00 0x01 so I’m guessing it is a NAL containing the PPS.

• YUV8_420P - AVFrame conversion hazard (only Y plan)

  4 mai 2017, par Flow

  I’m working on a FFMPEG application. The goal is to convert a picture (YUV input format) to an AVFrame to be able to process it (by applying a specific filter) and then realize the invert conversion to redirect it to the output.

  Although some filters as drawgrid or noise are perfectly working, filters which apply some "space transformation" (as a "crop" or a "hflip") seem to affect only over the Y component. The colors of the output pictures aren’t filtered which leads to an unsatisfying result.

  I’m asking myself why I have such a result but I didn’t reach to find the problem origin.

  Here is the part of cod which convert the YUV picture to an AVFrame :

  unsigned int i = 0;
  
  int number_common_channels = MIN(IMAGEFORMAT_COMPONENTS, AV_NUM_DATA_POINTERS);
  
  
  
  // Transfer the image informations (width, height, pitch and data)
  
  if ((av_im->width = yuv_im->width[0]) <= 0)
  
  {
  
      cu_printf(ERROR, "Width of destination picture null or negative");
  
      return -1;
  
  }
  
  if((av_im->height = yuv_im->height[0]) <= 0)
  
  {
  
      cu_printf(ERROR, "Height of destination picture null or negative");
  
      return -1;
  
  }
  
  for (i=0; i < number_common_channels; i++)
  
  {
  
      av_im->linesize[i] = yuv_im->pitch[i];
  
      av_im->data[i] = yuv_im->data[i];
  
  }

  If necessary, I can transmit you other parts of the cod where the problem could be. Thanks for your cooperation.

  Flow.

  EDIT 1 : After some researches, it would be possible the problem came from my function which initializes the filter graph. Actually, I used the FFMPEG example given on their website to make it and I deleted the options to the pixel format list because I thought it was useless. It’s possible this function and more precisely the av_opt_set_int_list could be the key, but I don’t reach to find a good example using it. Also, another function, av_opt_set_pixel_fmt was created in the last FFMPEG versions and this could be well to try using it, but I don’t know how to do. So please if someone has a good example with that, I’ll took it with hapiness.

  EDIT 2 : The problem came from the way I copied my data back after the filter was applied. Closed.