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• What's wrong with my use of timestamps/timebases for frame seeking/reading using libav (ffmpeg) ?

  17 septembre 2013, par mtree

  So I want to grab a frame from a video at a specific time using libav for the use as a thumbnail.

  What I'm using is the following code. It compiles and works fine (in regards to retrieving a picture at all), yet I'm having a hard time getting it to retrieve the right picture.

  I simply can't get my head around the all but clear logic behind libav's apparent use of multiple time-bases per video. Specifically figuring out which functions expect/return which type of time-base.

  The docs were of basically no help whatsoever, unfortunately. SO to the rescue ?

  #define ABORT(x) do {fprintf(stderr, x); exit(1);} while(0)
  
  
  
  av_register_all();
  
  
  
  AVFormatContext *format_context = ...;
  
  AVCodec *codec = ...;
  
  AVStream *stream = ...;
  
  AVCodecContext *codec_context = ...;
  
  int stream_index = ...;
  
  
  
  // open codec_context, etc.
  
  
  
  AVRational stream_time_base = stream->time_base;
  
  AVRational codec_time_base = codec_context->time_base;
  
  
  
  printf("stream_time_base: %d / %d = %.5f\n", stream_time_base.num, stream_time_base.den, av_q2d(stream_time_base));
  
  printf("codec_time_base: %d / %d = %.5f\n\n", codec_time_base.num, codec_time_base.den, av_q2d(codec_time_base));
  
  
  
  AVFrame *frame = avcodec_alloc_frame();
  
  
  
  printf("duration: %lld @ %d/sec (%.2f sec)\n", format_context->duration, AV_TIME_BASE, (double)format_context->duration / AV_TIME_BASE);
  
  printf("duration: %lld @ %d/sec (stream time base)\n\n", format_context->duration / AV_TIME_BASE * stream_time_base.den, stream_time_base.den);
  
  printf("duration: %lld @ %d/sec (codec time base)\n", format_context->duration / AV_TIME_BASE * codec_time_base.den, codec_time_base.den);
  
  
  
  double request_time = 10.0; // 10 seconds. Video's total duration is ~20sec
  
  int64_t request_timestamp = request_time / av_q2d(stream_time_base);
  
  printf("requested: %.2f (sec)\t-> %2lld (pts)\n", request_time, request_timestamp);
  
  
  
  av_seek_frame(format_context, stream_index, request_timestamp, 0);
  
  
  
  AVPacket packet;
  
  int frame_finished;
  
  do {
  
      if (av_read_frame(format_context, &packet) < 0) {
  
          break;
  
      } else if (packet.stream_index != stream_index) {
  
          av_free_packet(&packet);
  
          continue;
  
      }
  
      avcodec_decode_video2(codec_context, frame, &frame_finished, &packet);
  
  } while (!frame_finished);
  
  
  
  // do something with frame
  
  
  
  int64_t received_timestamp = frame->pkt_pts;
  
  double received_time = received_timestamp * av_q2d(stream_time_base);
  
  printf("received:  %.2f (sec)\t-> %2lld (pts)\n\n", received_time, received_timestamp);

  Running this with a test movie file I get this output :

      stream_time_base: 1 / 30000 = 0.00003
  
      codec_time_base: 50 / 2997 = 0.01668
  
  
  
      duration: 20062041 @ 1000000/sec (20.06 sec)
  
      duration: 600000 @ 30000/sec (stream time base)
  
      duration: 59940 @ 2997/sec (codec time base)
  
  
  
      requested: 10.00 (sec)  -> 300000 (pts)
  
      received:  0.07 (sec)   -> 2002 (pts)

  The times don't match. What's going on here ? What am I doing wrong ?

  ---

  While searching for clues I stumbled upon this this statement from the libav-users mailing list…

  [...] packet PTS/DTS are in units of the format context's time_base,
  where the AVFrame->pts value is in units of the codec context's time_base.

  In other words, the container can have (and usually does) a different
  time_base than the codec. Most libav players don't bother using the
  codec's time_base or pts since not all codecs have one, but most
  containers do. (This is why the dranger tutorial says to ignore AVFrame->pts)

  …which confused me even more, given that I couldn't find any such mention in the official docs.

  Anyway, I replaced…

  double received_time = received_timestamp * av_q2d(stream_time_base);

  …with…

  double received_time = received_timestamp * av_q2d(codec_time_base);

  …and the output changed to this…

  ...
  
  
  
  requested: 10.00 (sec)  -> 300000 (pts)
  
  received:  33.40 (sec)  -> 2002 (pts)

  Still no match. What's wrong ?

• Ffmpeg examples run in debug mode [on hold]

  25 août 2017, par Saeid Zangeneh

  I’m not so professional in c and cpp. I want to run FFmpeg official examples but there are many errors on include files. I can’t solve them.

  below output :when i try to run or debug the sample code

  debug output :

  cd '/home/saeid/NetBeansProjects/CppApplication_2'
  
  /usr/bin/make -f Makefile CONF=Debug
  
  "/usr/bin/make" -f nbproject/Makefile-Debug.mk QMAKE= SUBPROJECTS= .build-  conf
  
  make[1]: Entering directory '/home/saeid/NetBeansProjects
  
  /CppApplication_2'
  
  
  
  "/usr/bin/make"  -f nbproject/Makefile-Debug.mk dist/Debug/GNU-
  
  Linux/cppapplication_2
  
  
  
  make[2]: Entering directory '/home/saeid/NetBeansProjects
  
  /CppApplication_2'
  
  
  
  mkdir -p dist/Debug/GNU-Linux
  
  
  
  gcc     -o dist/Debug/GNU-Linux/cppapplication_2 build/Debug/GNU-
  
  Linux/sample.o 
  
  
  
  build/Debug/GNU-Linux/sample.o: In function `select_channel_layout':
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:87: undefined 
  
  reference to `av_get_channel_layout_nb_channels'
  
  
  
  build/Debug/GNU-Linux/sample.o: In function `audio_encode_example':
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:112: undefined 
  
  reference to `avcodec_find_encoder'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:117: undefined 
  
  reference to `avcodec_alloc_context3'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:127: undefined 
  
  reference to `av_get_sample_fmt_name'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:134: undefined 
  
  reference to `av_get_channel_layout_nb_channels'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:136: undefined 
  
  reference to `avcodec_open2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:146: undefined 
  
  reference to `av_frame_alloc'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:156: undefined 
  
  reference to `av_samples_get_buffer_size'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:162: undefined 
  
  reference to `av_malloc'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:169: undefined 
  
  reference to `avcodec_fill_audio_frame'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:179: undefined 
  
  reference to `av_init_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:183: undefined 
  
  reference to `sin'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:189: undefined 
  
  reference to `avcodec_encode_audio2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:196: undefined 
  
  reference to `av_free_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:201: undefined 
  
  reference to `avcodec_encode_audio2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:208: undefined 
  
  reference to `av_free_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:212: undefined 
  
  reference to `av_freep'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:213: undefined 
  
  reference to `av_frame_free'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:214: undefined 
  
  reference to `avcodec_close'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:215: undefined 
  
  reference to `av_free'
  
  
  
  build/Debug/GNU-Linux/sample.o: In function `audio_decode_example':
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:229: undefined 
  
  reference to `av_init_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:232: undefined 
  
  reference to `avcodec_find_decoder'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:237: undefined 
  
  reference to `avcodec_alloc_context3'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:243: undefined 
  
  reference to `avcodec_open2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:254: undefined 
  
  reference to `av_free'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:264: undefined 
  
  reference to `av_frame_alloc'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:269: undefined 
  
  reference to `avcodec_decode_audio4'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:276: undefined 
  
  reference to `av_get_bytes_per_sample'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:305: undefined reference to `avcodec_close'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:306: undefined reference to `av_free'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:307: undefined reference to `av_frame_free'

  build/Debug/GNU-Linux/sample.o : In function `video_encode_example’ :

  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:323: undefined reference to `avcodec_find_encoder'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:328: undefined reference to `avcodec_alloc_context3'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:350: undefined reference to `av_opt_set'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:352: undefined reference to `avcodec_open2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:361: undefined reference to `av_frame_alloc'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:371: undefined reference to `av_image_alloc'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:379: undefined reference to `av_init_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:399: undefined reference to `avcodec_encode_video2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:407: undefined reference to `av_free_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:413: undefined reference to `avcodec_encode_video2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:421: undefined reference to `av_free_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:427: undefined reference to `avcodec_close'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:428: undefined reference to `av_free'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:429: undefined reference to `av_freep'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:430: undefined reference to `av_frame_free'
  
  
  
  build/Debug/GNU-Linux/sample.o: In function `decode_write_frame':
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:452: undefined reference to `avcodec_decode_video2'

  build/Debug/GNU-Linux/sample.o : In function `video_decode_example’ :

  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:481: undefined reference to `av_init_packet'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:486: undefined reference to `avcodec_find_decoder'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:491: undefined reference to `avcodec_alloc_context3'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:502: undefined reference to `avcodec_open2'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:511: undefined reference to `av_frame_alloc'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:545: undefined reference to `avcodec_close'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:546: undefined reference to `av_free'
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:547: undefined reference to `av_frame_free'
  
  
  
  build/Debug/GNU-Linux/sample.o: In function `main':
  
  
  
  /home/saeid/NetBeansProjects/CppApplication_2/sample.c:556: undefined 
  
  reference to `avcodec_register_all'
  
  
  
  collect2: error: ld returned 1 exit status
  
  
  
  nbproject/Makefile-Debug.mk:62: recipe for target 'dist/Debug/GNU-
  
  Linux/cppapplication_2' failed
  
  
  
  make[2]: *** [dist/Debug/GNU-Linux/cppapplication_2] Error 1
  
  
  
  make[2]: Leaving directory '/home/saeid/NetBeansProjects/CppApplication_2'
  
  
  
  nbproject/Makefile-Debug.mk:59: recipe for target '.build-conf' failed
  
  
  
  make[1]: *** [.build-conf] Error 2
  
  
  
  make[1]: Leaving directory '/home/saeid/NetBeansProjects/CppApplication_2'
  
  
  
  nbproject/Makefile-impl.mk:39: recipe for target '.build-impl' failed
  
  
  
  make: *** [.build-impl] Error 2

• How to configure FFmpeg in windows ? [closed]

  2 août 2021, par GrassWarlock

  Hey there i'm not very tech savvy.

  


  when i invoke this command :

  


  ffmpeg -i input.mp4 -i subtitles.srt -map 0 -map 1 -c copy -c:v libx264 -crf 23 -preset veryfast output.mp4


  


  ( which is supposed to overlay 'input.mp4' with subtitles from 'subtitle.srt' )

  


  i get the following output :

  


  ffmpeg version 2021-07-27-git-0068b3d0f0-full_build-www.gyan.dev Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 10.3.0 (Rev5, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libdav1d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libglslang --enable-vulkan --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
  libavutil      57.  2.100 / 57.  2.100
  libavcodec     59.  3.102 / 59.  3.102
  libavformat    59.  4.101 / 59.  4.101
  libavdevice    59.  0.100 / 59.  0.100
  libavfilter     8.  1.103 /  8.  1.103
  libswscale      6.  0.100 /  6.  0.100
  libswresample   4.  0.100 /  4.  0.100
  libpostproc    56.  0.100 / 56.  0.100
Input #0, matroska,webm, from 'video.mkv':
  Metadata:
    ENCODER         : Lavf59.4.101
  Duration: 00:05:39.94, start: 0.000000, bitrate: 665 kb/s
  Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv), 720x480, SAR 1:1 DAR 3:2, 29.97 fps, 29.97 tbr, 1k tbn (default)
    Metadata:
      DURATION        : 00:05:39.839000000
  Stream #0:1: Audio: aac (LC), 44100 Hz, stereo, fltp (default)
    Metadata:
      HANDLER_NAME    : SoundHandler
      VENDOR_ID       : [0][0][0][0]
      DURATION        : 00:05:39.940000000
Input #1, srt, from 'subtitles.srt':
  Duration: N/A, bitrate: N/A
  Stream #1:0: Subtitle: subrip
[mp4 @ 000001aa596242c0] Could not find tag for codec subrip in stream #2, codec not currently supported in container
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 0:2 --
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
  Stream #1:0 -> #0:2 (copy)
    Last message repeated 1 times


  


  i searched the internet and the official documentation mentions that libass should be enabled in the configuration in order for subtitling to work

  


  


  11.218 subtitles

  


  Draw subtitles on top of input video using the libass library.

  


  To enable compilation of this filter you need to configure FFmpeg with
—enable-libass. This filter also requires a build with libavcodec and libavformat to convert the passed subtitles file to ASS (Advanced
Substation Alpha) subtitles format

  


  


  how do i enable libass in configuration on windows ? my FFmpeg directory doesn't contain a configuration file nor a command that configures it from cmd

  


  Thanks alot in advance