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• cuvid : Implement flush to support seeking in media players

  4 septembre 2016, par Philip Langdale

  cuvid : Implement flush to support seeking in media players
  Right now, if we attempt to use cuvid in a media player and then
  
  try to seek, the decoder will happily pass out whatever frames were
  
  already in flight before the seek.
  There is both the output queue in our code and some number of frames
  
  within the cuvid decoder that need to be accounted for.
  cuvid doesn’t support flush, so our only choice is to do a brute-force
  
  re-creation of the decoder, which also implies re-creating the parser,
  
  but this is fine.
  The only subtlty is that there is sanity check code in decoder
  
  initialisation that wants to make sure the HWContextFrame hasn’t already
  
  been initialised. This is a fair check to do at the beginning but not
  
  after a flush, so it has to be made conditional.
  Signed-off-by : Philip Langdale <philipl@overt.org>
  
  Signed-off-by : Timo Rothenpieler <timo@rothenpieler.org>
  

  • [DH] libavcodec/cuvid.c
  • [DH] libavcodec/version.h

• 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.

• Media Type Unrecognized with FFMPEG file generated

  2 août 2016, par pirmax

  I have an upload problem with the Twitter API.
  The problem is caused by codecs I think.

  I use FFMPEG to concatenate an audio file and an image, so to build a 30-second video to a file not exceeding in the 1MB.

  Here is the code that allows me to build this file and then upload the video via the Twitter API :

      var convert = function(image, audio, output) {
  
      var proc = ffmpeg(image)
  
      .loop(30)
  
      .addInput(audio)
  
      .format('mp4')
  
      .videoBitrate('1024k')
  
      .videoCodec('mpeg4')
  
      .size('640x640')
  
      .audioBitrate('128k')
  
      .audioChannels(2)
  
      .audioCodec('libfaac')
  
      .on('end', function() {
  
          console.log(output);
  
          fs.readFile(output, function(err, base64data) {
  
              client.post('media/upload', { media: base64data }, function (error, media, response) {
  
                  console.log(media);
  
              });
  
          });
  
      })
  
      .on('error', function(err) {
  
          console.log('an error happened: ' + err.message);
  
      })
  
      .save(output);
  
  };

  Each upload, I get the following message : unrecognized media type

  { request: '/1.1/media/upload.json',
  
    error: 'media type unrecognized.' }

  Could you help me please ? Thanks !