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• ffmpeg : Use actual frame dimensions in checks in sub2video_update()

  15 août 2015, par Michael Niedermayer

  ffmpeg : Use actual frame dimensions in checks in sub2video_update()
  Fixes Ticket4744 part2
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] ffmpeg.c

• How to find the actual size occupied by an AVFrame ?

  23 septembre 2013, par jsp99

  The main task at hand is to find the actual size of a decoded AVFrame.

  Here is some background information about the problem -
  I wrote a program which takes as input a media file and displays all the video frames of the file, on the screen. My Code (written in C using SDL and ffmpeg) worked perfectly with .wmv files. When it came to .mkv files, it failed (SIGSEGV) due to the following reason :

  Example : Suppose I have a decoded frame from my video stream of file (filename.mkv) in AVFrame *pFrame. The frame has a pix_fmt (pFrame->pix_fmt) of yuv420p. It has dimensions 640 * 346. The Y-plane has it's linesize (pFrame->linesize[0]) as 672.

  I think you get the point here. When I use avpicture_get_size() to get the size of the frame, it calculates a wrong size. It takes pix_fmt, width and height as arguments. Nowhere does it consider 672 instead of 640.

  avpicture_get_size() : Calculates the size in bytes that a picture of the given width and height would occupy if stored in the given picture format.

  I got around this problem by adding some yuv420p frame specific code, which can find the size of the frame in situations like above.

  • Can someone explain why are most of the decoded frames (from video streams of most of the formats) this way ? And why is it not this way with the wmv format ?

  But if I have to find the actual size occupied by an AVFrame of another format (Eg: yuv410p), I have to write the format specific code again. Coming to the main problem,

  • How can I find the actual size occupied the decoded AVFrame (size in bytes occupied by the data of the AVFrame) ?

  • I tried using av_image_get_buffer_size(), but I couldn't understand how to use the align parameter. Can someone explain the usage of the parameter align ? Tried using many other functions in pixdesc.c, but I am missing something.

• How to get actual PTS and DTS after frame decoding with libavcodec of FFmpeg

  17 décembre 2022, par Elija

  C++, FFmpeg, libavcodec, video frames decoding.

  


  To parse data from the network and split it into frames, I use the av_parser_parse2(_parser, _context, &_packet_encoded_frame->data, &_packet_encoded_frame->size, data, data_size, pts ? pts : AV_NOPTS_VALUE, dts ? dts : AV_NOPTS_VALUE, 0) function to which I pass non-zero values PTS and DTS as inputs.

  


  Next, I use the avcodec_send_packet(_context, _packet_encoded_frame) and avcodec_receive_frame(_context, _frame) functions to decode the frames.

  


  Why do I ALWAYS have PTS(_frame->pts) and DTS(_frame->pkt_dts) equal to AV_NOPTS_VALUE after SUCCESSFUL frame decoding ? How can I get the actual PTS and DTS values of that frame after decoding a frame ? What am I doing wrong ?