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• FFmpeg screencast recording : which codecs to use ?

  24 avril 2013, par mkaito

  I've been experimenting with recording screencasts using FFmpeg's X11grab module, which has worked more or less fine so far. I understand that a/v encoding is a complex process with many fine details, but I'm doing my best to learn.

  I'd like to do "lightweight" recording of a video stream, that puts as little strain as possible on the system while the stream is being recorded. I record two audio streams separately with pacat and sox. Later, the whole thing is filtered, normalized, encoded, and combined into a Matroska container.

  Right now, I'm having ffmpeg record a rawvideo stream to be fed to x264's yuv4 demuxer. I experimented with ffv1 and straight x264 recording before. My system can't handle real time encoding with x264 on the settings I want for the final stream, so I have to recompress separately once the recording is done. I've found that ffv1 gives me terrible frame dropping, and yuv4 too, but less so. I suspect this is due to hard drive speed, even if I'm sitting in a SATA3 Caviar Black that's being used exclusively to hold the recorded data.

  The question is, which combination of video codecs should I look at ? Record straight in x264 and recompress to "better" x264 later ? Raw video, then compress ? How would I go about pinpointing issues such as the frame drops I've been experiencing ?

  EDIT : This is the ffmpeg line I currently use.

  ffmpeg -v warning -f x11grab -s 1920x1080 -r 30000/1001 -i :0.0\
  
  -vcodec rawvideo -pix_fmt yuv420p -s 1280x720\
  
  -threads 0\
  
  recvideo.y4m

• FFmpeg X264 multithread decoding

  16 novembre 2013, par Xin He

  I want to do H264 multithread decoding using FFmpeg.
  First I use X264 to encode yuv420 to file.x264
  ./x264 -o file.x264 —slices 4 —input-res 1280x720 —fps 25 file_560x420.yuv

  The slices count is 4.

  However, when I use FFmpeg to decode,
  ./ffmpeg -y -threads 4 -thread_type slice -i file.x264 final.yuv

  FFmpeg calls func"execute_decode_slices" four times, not in a multithread way.
  I also found that in *execute_decode_slices(h, context_count)*, the context_count is 1.
  FFmpeg call this 4 times.

  Could someone help to solve this problem ?

  Thanks very much !

• Revision 644bd87e8e : In frame Q adjustment experiment. The idea here is to allow "in frame" adjustme

  22 novembre 2013, par Paul Wilkins

  Changed Paths :
   Modify /vp9/common/vp9_onyx.h

  
   Modify /vp9/encoder/vp9_encodeframe.c

  
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Modify /vp9/encoder/vp9_onyx_int.h

  
   Modify /vp9/encoder/vp9_ratectrl.c

  
   Modify /vpxenc.c

  
  
  In frame Q adjustment experiment.

  The idea here is to allow "in frame" adjustment of the final Q
  value used to encode each SB64, using segmentation.

  There is also adjustment of the rd mult in regions of overspend.

  Activated using aq_mode=2

  Change-Id : I2f140cd898c9f877c32cd6d2e667f5e11ada4b1c