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• What is the best way to get duration of a video using ffprobe (ffmpeg) ?

  15 juin 2023, par promaxdev

  Most of the solutions to get duration revolves around parsing the output to get the duration. Even FFProbe official documentation here says that there is no duration stored for MKV, webm, etc.

  


  Take the below examples.

  


  ffprobe -v error -i <inputmkv> -show_entries stream=...,duration,.. -of default=noprint_wrappers=1&#xA;</inputmkv>

  


  This gives me the below output. This is not having duration.

  


  

  


  But when I run the same command differently like below, I am getting this output but having duration. Just removed '-v error' part.

  


  ffprobe -i <inputmkv> -show_entries stream=...duration,... -of default=noprint_wrappers=1 &#xA;</inputmkv>

  


  

  


  If you notice the same command shows the duration in one place and not in another place.

  


  So my question is, What is the best way to get duration in ffmpeg, especially for the video streams ?

  


  Edit : I have already explored decoding using null mux option. But that is a costly operation and also need to parse the output.

  


• How to force AVCodecContext to release all references to any buffers

  17 septembre 2024, par imikbox

  I'm using FFMPEG to decode a video stream and I have implemented a custom functions for AVFrame memory allocation and de-allocation (by setting a custom function for codec_ctx->get_buffer2). So when an AVFrame requires new memory, I do the memory allocation and wrap an AvBufferRef around it using av_buffer_create. I also define my custom de-allocation function, so when the reference counted AvBufferRef is not required anymore, I do the memory clean up.
This way I can log precisely when memory gets allocated and when a buffer becomes free.

  


  During video decoding I want to do a seek, for that I need to clear out all buffers from my AVCodecContext. I'm following the official documentation for that :

  


  

  • enter draining mode by sending NULL to the decoder

  


  • collect all frames from the decoder

  


  • flush AVCodecContext

  


  


  This is the code for that :

  


          avcodec_send_packet(codec_ctx, NULL);
        auto result = 0;
        while (result != AVERROR_EOF)
        {
            auto frame = av_frame_alloc();
            result = avcodec_receive_frame(codec_ctx, frame);
            av_frame_free(&frame);
        }
        avcodec_flush_buffers(codec_ctx);


  


  However, I can see (due to my custom memory management) that not all frames are released.
Only when I close the codec context by calling avcodec_free_context, I see all frames getting released.

  


  Any hints how I can completely release all resources in AVCodecContext (without closing it) ?

  


• Compiling FFmpeg with option —enable-libass on CentOS 5 32bit [closed]

  26 mai 2012, par whatUwant

  I have already installed libass and libass-devel

  yum install libass libass-devel
  
  ...
  
  Package libass-0.9.11-1.el5.rf.i386 already installed and latest version
  
  Package libass-devel-0.9.11-1.el5.rf.i386 already installed and latest version
  
  Nothing to do

  The source code of ffmpeg is from official git.
  I try to compile ffmpeg with the option —enable-libass. But it prompts "ERROR : libass not found" every time.

  ./configure --enable-version3 \
  
  --enable-libvorbis \
  
  --enable-libx264 \
  
  --enable-libxvid \
  
  --disable-ffplay \
  
  --enable-shared \
  
  --enable-libmp3lame \
  
  --enable-gpl \
  
  --enable-pthreads \
  
  --enable-postproc \
  
  --enable-x11grab \
  
  --enable-libgsm  \
  
  --enable-swscale \
  
  --enable-nonfree \
  
  --enable-avfilter \
  
  --enable-libass

  In config.log it says

  check_pkg_config libass ass/ass.h ass_library_init
  
  ERROR: libass not found

  I've checked

  /usr/local/include/ass/ass.h

  and

  /usr/include/ass/ass.h

  this ass.h does exist in both places.

  "pkg-config —cflags —libs libass" says

  Package enca was not found in the pkg-config search path.
  
  Perhaps you should add the directory containing `enca.pc'
  
  to the PKG_CONFIG_PATH environment variable
  
  Package 'enca', required by 'libass', not found

  "yum install enca" says

  Package enca-1.10-1.el5.rf.i386 already installed and latest version