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• ffplay : Use sws_scale to scale subtitles

  26 juillet 2015, par Michael Niedermayer

  ffplay : Use sws_scale to scale subtitles
  Fixes some files from Ticket679
  This also changes subtitles to 4:2:0 matching the output format and thus
  
  simplifying the blend code.
  
  This restricts placement to the chroma sample resolution though, speak up
  
  if you consider this a problem, say so, the code could be changed to use
  
  YUV444 for subtitles and scaling them down while blending, this would be
  
  slower though.
  
  The current code only uses a single swscale context and reinitializes it
  
  as needed, this could be changed as well if needed
  Reviewed-by : Marton Balint <cus@passwd.hu>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] ffplay.c

• libav/ffmpeg : avcodec_decode_video2() returns -1 when separating demultiplexing and decoding

  26 avril 2013, par unbekannt

  I'm using libav (from a C++ program on Linux and Windows) to decode video streams from a file, which works fine (decoding various formats like H264 and MPEG2) using avformat_open_input(), av_read_frame() and avcodec_decode_video2().

  Now I have to separate demultiplexing and decoding. One class will call avformat_open_input() and av_read_frame() and then pass the AVPackets into a queue that is read by another class. There I use avcodec_alloc_context3() to get the AVCodecContext needed for avcodec_decode_video2(). I've tested that with a MPEG2 video stream and it works.

  Problems arise if I try to decode a H264 stream : avcodec_decode_video2() always returns -1 and outputs "no frame". I understand that additional data (SPS/PPS) is needed to decode this stream, so I've tried to replicate the original AVCodecContext from the demultiplexer in the decoder, but it won't work :

  • Copying the content of the extradata field and setting all other values that differ from the default ones in the decoder : -1 is returned
  • Using the same context (i.e. passing along the pointer) results in a crash

  I also tried to set CODEC_FLAG2_CHUNKS. avcodec_decode_video2() then always returns packet.size - 3 (??) and frameFinished is never set to 1.

  In my opinion I have a general problem here that will arise whenever settings from the original CodecContext are needed to decode the AVPackets. I'd be grateful for any hints on how to solve that problem !

  EDIT : Sometimes writing down your problem helps solving it... Using a copy of the context struct (avcodec_copy_context) and opening the codec only after receiving the copy results in decoded frames. Does anyone know if that is safe or the best way to do it ?

• avformat : Append data in fill_buffer() when possible

  30 juin 2013, par Michael Niedermayer

  avformat : Append data in fill_buffer() when possible
  Data is appended in fill_buffer() when there is sufficient space left
  
  and the data pointer only reset when needed.
  
  Previously the data pointer was more often reset, loosing more seekback
  
  space than otherwise needed.
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavformat/aviobuf.c