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• Animation speed adjustment using ffmpeg in Python

  5 novembre 2015, par neither-nor

  I’m been for years using stock ffmpeg script to sequentially snitch together temporal plots in Python. However, I cannot figure out the trivial issue of how to, for instance, slow down the animation speed so that the resultant video file has a longer duration.

  Example :

  import matplotlib.pyplot as plt
  
  import os, sys
  
  
  
  for t in range(100):
  
      plt.cla()
  
      plt.text(0.5, 0.5, 'time %02d'%(t+1))
  
      plt.draw()
  
  
  
      fname = '_tmp%02d.png'%(t+1)
  
      plt.savefig(fname)
  
  
  
  os.system("ffmpeg -i _tmp%02d.png -pix_fmt yuv420p -r 20 -b:v 20M flipbook.mp4")
  
  os.system("rm _tmp*.png")    

  The resulting "flip book" takes 4s and the time stamp increases steadily. However, I tried to make the animation last twice as long by testing the following :

  1. Change 20 after -r to 1 : this still lasts 4s but now the time stamp "leaps" nonlinearly

  2. Change 20M to 1M : no discernible effect

  I can’t find much information about this line of code, either the usage of each flag or how to modify aspects of it (e.g.,speed).

• Extracting video frame image with libavformat and libswscale gives flipped image

  21 novembre 2015, par ivan.ukr

  I am using following code to extract image frames outputted by avcodec_decode_video2() into BMP file :

  // Convert the image from its native format to RGB
  
  int height = sws_scale(state.sws_ctx, 
  
               (uint8_t const * const *)state.frame->data,
  
               state.frame->linesize, 
  
               0, 
  
               state.video_codec_ctx->height,
  
               state.picture.data, 
  
               state.picture.linesize);
  
  
  
  // ..... here BMP header initialization goes ...
  
  
  
  // Extract pixels
  
  {
  
      int y = 0;
  
      size_t frame_line_size = state.picture.linesize[0];
  
      uint8_t* bmp_data = &bmp->data[0];
  
      uint8_t* picture_data = state.picture.data[0];
  
      while(y < height)
  
      {
  
          memcpy(bmp_data, picture_data, image_line_size);
  
          bmp_data += image_line_size_with_padding;
  
          picture_data += frame_line_size;
  
          ++y;
  
      }
  
  }

  But it results flipped image :

  

  Can anyone please help me to understand, what I am doing wrong here ?

  Video stream information :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'testdata/video3.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      creation_time   : 1970-01-01 00:00:00
  
      title           : video3.mp4
  
      encoder         : Lavf52.78.3
  
    Duration: 00:00:07.93, start: 0.000000, bitrate: 1467 kb/s
  
      Stream #0.0(und): Video: h264 (High), yuv420p, 640x320 [PAR 1:1 DAR 2:1], 1331 kb/s, 29.73 fps, 29.73 tbr, 29734 tbn, 59.47 tbc
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
      Stream #0.1(und): Audio: aac, 48000 Hz, stereo, fltp, 127 kb/s
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
  Video file 'testdata/video3.mp4' has 236 frames.

  I have alternate code that uses libopencv, and it gives correct image from the same video file, but I need to reach the correct effect using directly ffmpeg libs.

  

• mp4,m4v vidoes not play on firefox

  20 novembre 2015, par Waqas Ahad

  Using paperclip-ffmpeg for video uploading in Rails.
  It plays on Chrome but not on Firefox and throws :

  Video format or MIME type is not supported

  I have this code in my model :

  has_attached_file :videod, :styles => { 
  
                          medium => { :geometry => "640x480", :format => 'mp4' },
  
                         :thumb => { :geometry => "100x100#", :format => 'jpg', :time => 10 }
  
  }, :processors => [:ffmpeg]
  
  validates_attachment_size :videod, :less_than => 100.megabytes
  
  validates_attachment_presence :videod
  
  validates_attachment_content_type :videod, :content_type => /\Avideo\/.*\Z/

  I also installed ubuntu-restricted-extras which was required to play it on firefox.

  Result of ffprobe :

  ffprobe version 2.4.3-1ubuntu1~trusty6 Copyright (c) 2007-2014 the FFmpeg developers
  
  built on Nov 22 2014 17:07:19 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  
  configuration: --prefix=/usr --extra-version='1ubuntu1~trusty6' --build-suffix=-ffmpeg --toolchain=hardened --extra-cflags= --extra-cxxflags= --libdir=/usr/lib/x86_64-linux-gnu --shlibdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --enable-shared --disable-stripping --enable-avresample --enable-avisynth --enable-fontconfig --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-opengl --enable-x11grab --enable-libxvid --enable-libx265 --enable-libdc1394 --enable-libiec61883 --enable-libzvbi --enable-libzmq --enable-frei0r --enable-libx264 --enable-libsoxr --enable-openal --enable-libopencv
  
    libavutil      54.  7.100 / 54.  7.100
  
    libavcodec     56.  1.100 / 56.  1.100
  
    libavformat    56.  4.101 / 56.  4.101
  
    libavdevice    56.  0.100 / 56.  0.100
  
    libavfilter     5.  1.100 /  5.  1.100
  
    libavresample   2.  1.  0 /  2.  1.  0
  
    libswscale      3.  0.100 /  3.  0.100
  
    libswresample   1.  1.100 /  1.  1.100
  
    libpostproc    53.  0.100 / 53.  0.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'SampleVideo_360x240_2mb.mp4':
  
  Metadata:
  
    major_brand     : isom
  
    minor_version   : 512
  
    compatible_brands: isomiso2avc1mp41
  
    creation_time   : 1970-01-01 00:00:00
  
    encoder         : Lavf53.24.2
  
  Duration: 00:00:26.80, start: 0.000000, bitrate: 626 kb/s
  
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 320x240 [SAR 1:1 DAR 4:3], 239 kb/s, 15 fps, 15 tbr, 15360 tbn, 30 tbc (default)
  
  Metadata:
  
    creation_time   : 1970-01-01 00:00:00
  
    handler_name    : VideoHandler
  
  Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 383 kb/s (default)
  
  Metadata:
  
    creation_time   : 1970-01-01 00:00:00
  
    handler_name    : SoundHandler

  After ffmpeg -i :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'SampleVideo_360x240_2mb.mp4':
  
  Metadata:
  
    major_brand     : isom
  
    minor_version   : 512
  
    compatible_brands: isomiso2avc1mp41
  
    creation_time   : 1970-01-01 00:00:00
  
    encoder         : Lavf53.24.2
  
  Duration: 00:00:26.80, start: 0.000000, bitrate: 626 kb/s
  
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 320x240 [SAR 1:1 DAR 4:3], 239 kb/s, 15 fps, 15 tbr, 15360 tbn, 30 tbc (default)
  
  Metadata:
  
    creation_time   : 1970-01-01 00:00:00
  
    handler_name    : VideoHandler
  
  Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 383 kb/s (default)
  
  Metadata:
  
    creation_time   : 1970-01-01 00:00:00
  
    handler_name    : SoundHandler