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• Libav (ffmpeg) What is the most robust way to set the output stream time base ?

  29 octobre 2016, par Jason C

  This is a follow up to the solution to this question. My question is : When creating a new output stream, what is the most robust way to ensure that the output stream time base is set to a valid value for arbitrary formats ?

  Another way to phrase this question is : If I leave the output stream time base set to 0/0, will avformat_write_header always initialize it to something appropriate ?

  Consider the following snippet (assume, unlike the above linked question, that I’m just encoding video and I do not have any input video timing info to refer to or copy from) :

  AVFormatContext *formatx;
  
  AVCodec *codec;
  
  AVStream *stream;
  
  ...
  
  stream = avformat_new_stream(formatx, codec);
  
  stream->time_base = { 1, 10000 };
  
  ...
  
  avformat_write_header(formatx, NULL);

  Here, my rationale is as follows :

  • I observed, for MOV output formats, that if the stream time base is 0/0 when avformat_write_header is called, it is changed to 1/90000. Conclusion : At least one format (MOV) has a preferred time base that is set here, so others may be the same.
  • I do not know if avformat_write_header can be relied on to do this first, so I figure I’ll give it an initial reasonable value (1/10000) just in case.

  So this covers cases where avformat_write_header doesn’t set the time base. However, now I’ve observed two worrisome things :

  • If I do initialize the time base (to 1/10000 in this case), avformat_write_header does not modify it. No worries yet, except...
  • As an experiment I set it to 1/1000000. The MOV muxer issued a warning that the time base was too high. This means avformat_write_header seems to obey the time base that was set even if it’s not necessarily appropriate for the muxer.

  So my conflict is as follows :

  • If I don’t set the time base before writing the header, then I know that in at least some cases avformat_write_header will initialize it to something appropriate. However, I don’t know if this is true in all cases, so I run the risk of this failing (or do I ? that’s the question here).
  • If I do set the time base before writing the header, then I’m safe in situations where avformat_write_header doesn’t, but I run the risk of breaking the muxer, since I can’t know what time bases are valid for arbitrary muxers (or can I ?)
  • The time base can’t be changed after writing the header, of course. So I can’t initialize it to 0/0 then check it for validity and set it to something afterwards. That is, if I set it to 0/0, and avformat_write_header does not fill it in, then I’ve missed an opportunity to set it myself and the program unnecessarily fails.

  So what do I do ? How do I ensure that an output stream time base is both a) always set, and b) always set to something appropriate for the muxer ?

• Directshow how to use Monogram X264 Encoder to capture video from webcam ?

  17 août 2016, par Phung Tien Trieu

  I am new with Directshow. Today i am trying to use Monogram x264 encoder filter with GraphStudioNext. But when i connect camera to monogram x264 encoder filter. There is an error. I don’t know what intermediate filter do i need. Can you please help ?

  See the picture : http://tientrieu.net/wp-content/uploads/2016/08/how_to_use_monogram_x264_encoder.png

• libFLAC/cpu.c : Remove OS SSE detection

  4 décembre 2016, par Erik de Castro Lopo

  libFLAC/cpu.c : Remove OS SSE detection
  Assume that all OSes that are usable today support SSE.
  Patch-from : lvqcl.mail <lvqcl.mail@gmail.com>
  

  • [DH] src/libFLAC/cpu.c