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• How to correctly combine FFMPEG file pattern and complex filter ?

  4 octobre 2015, par John Doe

  Say I have the following FFMPEG command line using the built-in filters.

  ffmpeg -y -loop 1 -t 1 -i 'img-0001.jpg' -loop 1 -t 1 -i 'img-0002.jpg' \
  
  -filter_complex "\
  
  [1:v][0:v]blend=all_expr='A*(if(gte(T,0.7),1,T/0.7))+B*(1-(if(gte(T,0.7),1,T/0.7)))'[b1v]; \
  
  [0:v][b1v][1:v]concat=n=3:v=1:a=0,format=yuv420p[v]" \
  
  -map "[v]" out.avi

  What it does is to display the two input images img-0001.jpg and img-0002.jpg for one second each and also blending between them. Unfortunatly this will break at some point when I want to create a slide show with a lot of images. You will get an "Argument list too long" error. So I wanted to use ffmpegs file pattern syntax, i.e., something like

  ffmpeg -y -loop 1 -t 1 -i 'img-%04d.jpg'  \
  
  -filter_complex "\
  
  [1:v][0:v]blend=all_expr='A*(if(gte(T,0.7),1,T/0.7))+B*(1-(if(gte(T,0.7),1,T/0.7)))'[b1v]; \
  
  [0:v][b1v][1:v]concat=n=3:v=1:a=0,format=yuv420p[v]" \
  
   -map "[v]" out.avi

  As far as I understood the syntax, the file names should be okay for this scenario. The files under test are the same as the ones explicitly stated in the first command. But I cannot manage to get passed the following error :

  Input #0, image2, from 'img-%04d.jpg':
  
  Duration: 00:00:00.08, start: 0.000000, bitrate: N/A
  
  Stream #0:0: Video: mjpeg, yuvj422p(pc, bt470bg/unknown/unknown), 2592x1728     [SAR 72:72 DAR 3:2], 25 fps, 25 tbr, 25 tbn, 25 tbc
  
  Invalid file index 1 in filtergraph description [1:v][0:v]blend=all_expr='A* (if(gte(T,0.7),1,T/0.7))+B*(1-(if(gte(T,0.7),1,T/0.7)))'[b1v]; [0:v][b1v]   [1:v]concat=n=3:v=1:a=0,format=yuv420p[v].

  It looks like I am using the file pattern syntax wrong. What am I missing ?
  Thanks in advance.

• Add attachment to Matroska (mkv) programmatically after video write

  2 mai 2016, par Faber

  I want to add a protobuf message as attachment to a Matroska (mkv) video file after all video frames have been written without copying the video data. This must be possible because attaching an arbitrary file to an mkv can be achieved with the MKVToolNix suite (for a JPG) :

  # add attachment, no copy according to man page
  
  mkvpropedit out.mkv --add-attachment ~/Downloads/hummingbird.jpg
  
  .
  
  .
  
  # get attachment id
  
  mkvmerge -i out.mkv
  
  .
  
  Attachment ID 1: type 'image/jpeg', size 821740 bytes, file name 'hummingbird.jpg'
  
  .
  
  # extract attachment
  
  mkvextract attachments out.mkv 1:./test.jpg

  I want to be capable to perform the same read-write-cycle by calling library methods. Preferably without the need to write the protobuf message to a file first (e.g. by passing a byte array of the serialized protobuf message).

  Currently I’m using libav for reading/writing video data from/to mkv. Therefor my favorite solution would also only depend on libav. If this is not possible I would consider introducing libEBML and libMatroska as new dependencies (same as MKVToolNix).

  What are the key functions in the frameworks that need to be called to achieve the goal ? I’m pretty sure mbunkus knows the solution ...

• Can I pipe pygame output to a utility like ffmpeg if I am on Windows ?

  20 septembre 2015, par user89

  Usually, pygame shows its output in a specially created window. Instead of creating this window, then saving images in sequence from it, before finally feeding these images to a tool like ffmpeg, I’d like to pipe pygame’s output directly ffmpeg.

  Does what I want make sense ?

  If yes, how can I redirect pygame’s output to console ? From the documentation, I am aware of methods like pygame.Surface.get_view or pygame.Surface.get_buffer, but I don’t know what the difference is between them, and whether they are quite what I need.

  In this tutorial, a raw numpy-array based RGB representation of images is fed to ffmpeg. I figure I could do a similar thing, except instead I’d feed in some sort of RGB representation obtained from pygame.

  I know that on Linux, it’s possible to output pygame stuff to a framebuffer for display in the console ? Not sure if it is related. In any case, the effect is achieved by changing pygame drivers.

  So, I have some dots, but need to connect them.