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• FFMPEG video conversion

  10 février 2014, par user3292775

  I want to know what methods does the FFMPEG has. In the documentation provided on FFMPEG official site there is no information of the methods that can be used. Any help would be much appreciated.

• How can I automatically embed commit information into a subtitles file that I'm tracking ?

  23 février 2015, par microspace

  I use git to track *.ass subtitle files.
  Here is example of *.ass file :

  [Script Info]
  
  ; Script generated by Aegisub 3.1.2
  
  ; http://www.aegisub.org/
  
  Title: Default Aegisub file
  
  ScriptType: v4.00+
  
  
  
  [V4+ Styles]
  
  Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour,    BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
  
  Style: Default,Arial,20,&H00FFFFFF,&H000000FF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,1,2,2,2,10,10,10,1
  
  Style: titr,DejaVu     
  
  
  
  Sans,20,&H007DDBFA,&H000000FF,&H00000000,&HFF000000,0,0,0,0,100,100,0,0,1,2,2,1,10,10,10,1
  
  
  
  [Events]
  
  Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
  
  Dialogue: 0,0:00:00.46,0:00:11.22,Default,,0,0,0,,Если это можно было бы
  
  Dialogue: 0,0:00:03.44,0:00:08.96,titr,,0,0,0,,{\pos(20,240)\fad(600,600)}бывший министр

  After commit I burn subtitles into video :

  ffmpeg -i video.avi -vf "ass=subtitle.ass" out.avi

  My goal is to show commit date for 10 second at the start of movie. This should be done automatically.

  1) It can be easily done with by modifying subtitle.ass itself, but I can’t do it after commit and there are other reasons.

  2) It can be done by ffmpeg from command line : How to use ffmpeg to add a text to avi video ?

  Problem is that in this case text will be shown for the whole lenght of movie.

  3) I can copy *.ass file to temporary directory, insert date, render and delete *.ass file.

  Is there a simpler way ?

• Frame Accurate Seeking in WebM

  11 janvier 2016, par SapphireSun

  I’m trying to do a somewhat tricky thing with WebM. I am trying to encode a stack of 256 biological images as a WebM. The time dimension of motion is very similar to the space dimension of the image stack so the compression ratios are insanely good. However, I am having trouble decoding the movie frames. I know that WebM uses an IPB predictive coding scheme, but I was reading several blog posts and discussion groups from WHATWG from 2011, and they said that frame accurate seeking was working in Chrome at that time.

  When I do video.currentTime = 0, I correctly get this :

  

  However, if I do video.currentTime = 0.34 (for example) I get something that looks like this :

  

  It looks like I’m getting a random poorly predicted frame. Am I just encoding the video wrong ? When I play it normally it looks fine.

  I encoded the video using 256 pngs using ffmpeg compiled with libvpx using the VP8 codec.

  ffmpeg -y -framerate 60 -start_number 0 -pattern_type glob -i '*.png' -qmin 10 -qmax 42 out.webm

  References to the WHATWG and some other info from 2011 :

  WHATWG discusses frame accuracy :

  https://lists.w3.org/Archives/Public/public-whatwg-archive/2011Jan/0372.html

  BBC Tech Director talking about frame accuracy :

  http://www.bbc.co.uk/blogs/bbcinternet/2011/02/frame_accurate_video_in_html5.html