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• ffmpeg audio synch issue - fractional framerate

  29 mars 2013, par JoeCitizen

  We are working on an Android app which uses the ffmpeg library via JNI to edit the frames of a video while keeping size, codec etc the same.

  We are having an issue where the audio of the output video is getting out of sync with the video. We believe this is because some input videos have a frame rate which isn't a whole number e.g 25.66 fps and our output will be at 25fps. We have tried to change the time_base field of the output codec to keep the precision i.e by multiply the numerator and denominator but it makes the output frame rate ridiculously high.

  Does anyone know how to force ffmpeg to use the exact same output frame rate as the one it reads in ? We have not found a way to output videos with a fractional frame rate.

  Example of setting up the output codec :

      c =                 st->codec;
  
      c->codec_id =       codec_id;
  
      c->codec_type =     AVMEDIA_TYPE_VIDEO;
  
      c->bit_rate =       inputCodecCtx->bit_rate;
  
      c->width =          inputCodecCtx->width;
  
      c->height =         inputCodecCtx->height;
  
  
  
      c->time_base.num =   1000;
  
      c->time_base.den =  (int)(fps*1000);//fps of the input video *1000 to keep precision
  
  
  
      c->gop_size =       inputCodecCtx->gop_size;
  
      c->pix_fmt =        inputCodecCtx->pix_fmt;
  
  
  
  
  
  
  
      static int write_video_frame(AVFormatContext *oc, AVStream *st, AVFrame *newpict, double fps)
  
      {
  
          int             ret = 0;
  
          AVCodecContext* c = st->codec;
  
  
  
          AVPacket pkt;
  
          av_init_packet(&pkt);
  
  
  
          if (pkt.pts != AV_NOPTS_VALUE)
  
          {
  
              pkt.pts =  av_rescale_q(c->coded_frame->pts, c->time_base, st->time_base);
  
  
  
          }
  
          if (pkt.dts != AV_NOPTS_VALUE)
  
  
  
  
  
          {
  
              pkt.dts = av_rescale_q(c->coded_frame->pts, c->time_base, st->time_base);
  
          }
  
  
  
  .....
  
  }

• Grab partial .mp4 video from onlline source

  28 juillet 2016, par Flemingjp

  I want to be able to grab a partial mp4 file from an online source so I can produce quick thumbnails.

  My idea was to pull a patial mp4 file from a http request using the header

  Range: 'bytes=1000-'

  However when I parse the data it doesn’t have the mp4 container therefore is corrupt. In Firefox it handles this easily as seeking to an unloaded part of the video is very quick.

  How can I pull partial mp4 clips ? For example from here I could get a clip that is 0:28-0:30

• Writing an MP4 file on the Mac with OpenCV ffmpeg

  13 janvier 2015, par Sameer Parekh

  I am using OpenCV with ffmpeg on a mac to write video. I’ve been able to successfully write .avi files using the codec/fourcc code, FMP4. I would like to write .mp4 files, however. When I try to write an .mp4 file using fourcc FMP4 I get this error :

  [mp4 @ 0x100b4ec00] Tag FMP4/0x34504d46 incompatible with output codec id '13' ( [0][0][0])

  When I use AVC1 I get the following error :

  [libx264 @ 0x104003000] broken ffmpeg default settings detected
  
  [libx264 @ 0x104003000] use an encoding preset (e.g. -vpre medium)
  
  [libx264 @ 0x104003000] preset usage: -vpre <speed> -vpre <profile>
  
  [libx264 @ 0x104003000] speed presets are listed in x264 --help
  
  [libx264 @ 0x104003000] profile is optional; x264 defaults to high
  
  Could not open codec 'libx264': Unspecified error
  
  </profile></speed>

  Does anyone here know the right codec to use with OpenCV and ffmpeg to write to an MP4 container on the Mac ?

  If AVC1 is the right codec, how do I install ffmpeg + OpenCV correctly ? I did

  brew install gpac
  
  brew install ffmpeg
  
  brew install opencv

  The call I am using to open the videowriter :

  fourcc = cv2.cv.CV_FOURCC('A', 'V', 'C', '1')   
  
  video_out = cv2.VideoWriter(
  
      filename=output_filename,
  
      fourcc=fourcc,
  
      fps=video_fps,
  
      frameSize=(video_width,video_height),
  
      isColor=1)

  When I run x264 --help I get

  % x264 --help
  
  x264 core:125
  
  Syntax: x264 [options] -o outfile infile
  
  
  
  Infile can be raw (in which case resolution is required),
  
    or YUV4MPEG (*.y4m),
  
    or Avisynth if compiled with support (no).
  
    or libav* formats if compiled with lavf support (no) or ffms support (no).
  
  Outfile type is selected by filename:
  
   .264 -> Raw bytestream
  
   .mkv -> Matroska
  
   .flv -> Flash Video
  
   .mp4 -> MP4 if compiled with GPAC support (no)
  
  Output bit depth: 8 (configured at compile time)
  
  
  
  Options:
  
  
  
    -h, --help                  List basic options
  
        --longhelp              List more options
  
        --fullhelp              List all options
  
  
  
  Example usage:
  
  
  
        Constant quality mode:
  
              x264 --crf 24 -o <output> <input />
  
  
  
        Two-pass with a bitrate of 1000kbps:
  
              x264 --pass 1 --bitrate 1000 -o <output> <input />
  
              x264 --pass 2 --bitrate 1000 -o <output> <input />
  
  
  
        Lossless:
  
              x264 --qp 0 -o <output> <input />
  
  
  
        Maximum PSNR at the cost of speed and visual quality:
  
              x264 --preset placebo --tune psnr -o <output> <input />
  
  
  
        Constant bitrate at 1000kbps with a 2 second-buffer:
  
              x264 --vbv-bufsize 2000 --bitrate 1000 -o <output> <input />
  
  
  
  Presets:
  
  
  
        --profile <string>      Force the limits of an H.264 profile
  
                                    Overrides all settings.
  
                                    - baseline,main,high,high10,high422,high444
  
        --preset <string>       Use a preset to select encoding settings [medium]
  
                                    Overridden by user settings.
  
                                    - ultrafast,superfast,veryfast,faster,fast
  
                                    - medium,slow,slower,veryslow,placebo
  
        --tune <string>         Tune the settings for a particular type of source
  
                                or situation
  
                                    Overridden by user settings.
  
                                    Multiple tunings are separated by commas.
  
                                    Only one psy tuning can be used at a time.
  
                                    - psy tunings: film,animation,grain,
  
                                                   stillimage,psnr,ssim
  
                                    - other tunings: fastdecode,zerolatency
  
  
  
  Frame-type options:
  
  
  
    -I, --keyint <integer or="or"> Maximum GOP size [250]
  
        --tff                   Enable interlaced mode (top field first)
  
        --bff                   Enable interlaced mode (bottom field first)
  
        --pulldown <string>     Use soft pulldown to change frame rate
  
                                    - none, 22, 32, 64, double, triple, euro (requires cfr input)
  
  
  
  Ratecontrol:
  
  
  
    -B, --bitrate <integer>     Set bitrate (kbit/s)
  
        --crf <float>           Quality-based VBR (0-51) [23.0]
  
        --vbv-maxrate <integer> Max local bitrate (kbit/s) [0]
  
        --vbv-bufsize <integer> Set size of the VBV buffer (kbit) [0]
  
    -p, --pass <integer>        Enable multipass ratecontrol
  
                                    - 1: First pass, creates stats file
  
                                    - 2: Last pass, does not overwrite stats file
  
  
  
  Input/Output:
  
  
  
    -o, --output <string>       Specify output file
  
        --sar width:height      Specify Sample Aspect Ratio
  
        --fps   Specify framerate
  
        --seek <integer>        First frame to encode
  
        --frames <integer>      Maximum number of frames to encode
  
        --level <string>        Specify level (as defined by Annex A)
  
        --quiet                 Quiet Mode
  
  
  
  Filtering:
  
  
  
        --vf, --video-filter <filter0>/<filter1>/... Apply video filtering to the input file
  
  
  
        Filter options may be specified in <filter>:<option>=<value> format.
  
  
  
        Available filters:
  
        crop:left,top,right,bottom
  
        select_every:step,offset1[,...]
  
  </value></option></filter></filter1></filter0></string></integer></integer></string></integer></integer></integer></float></integer></string></integer></string></string></string></output></output></output></output></output></output>

  Thanks,
   s