According to this articleI used successfully the command$ ffmpeg -vf select='eq(pict_type,I)' -i somevideo.mp4 -vsync 0 -f image2 /tmp/thumbnails-%02d.jpgI tried the second command:$ ffmpeg -vf select='gt(scene\,0.9)' -i somevideo.mp4 -vsync 0 -f image2 /tmp/thumbnails-%02d.jpgbut ended with error:Undefined constant or missing '(' in 'scene'Because$ ffmpeg -versionffmpeg version 0.8.17-4:0.8.17-0ubuntu0.12.04.1, Copyright (c) 2000-2014 the Libav developers  built on Mar 16 2015 13:28:23 with gcc 4.6.3The ffmpeg program is only provided for script compatibility and will be removedin a future release. It has been deprecated in the Libav project to allow forincompatible command line syntax improvements in its replacement called avconv(see Changelog for details). Please use avconv instead.ffmpeg 0.8.17-4:0.8.17-0ubuntu0.12.04.1libavutil    51. 22. 3 / 51. 22. 3libavcodec   53. 35. 0 / 53. 35. 0libavformat  53. 21. 1 / 53. 21. 1libavdevice  53.  2. 0 / 53.  2. 0libavfilter   2. 15. 0 /  2. 15. 0libswscale    2.  1. 0 /  2.  1. 0libpostproc  52.  0. 0 / 52.  0. 0I tried to use rather avconv. It runs both commands successfully, but in both cases it generates incorrect results (too many frames, so seemingly ignoring the video filter expression).How can I correct my ffmpeg or avconv to give the right results?
Incorrect scene change detection with avconv
command line;video;ffmpeg;avconv;video editing
First of all,-vf needs to be specified after the input in order to affect it, and it seems to be the only reason avconv worked for the second command: it must have discarded your filter without even parsing it. If you move the argument after -i, it will result in the same error as ffmpeg gave you. Newer versions of ffmpeg actually treat that as an error.Now the reason why neither of the commands are working is simple: neither of the versions that you are using support the scene filter.What's more, the scene filter still appears to be missing in the master branch of  avconv as of now, thus, avconv simply does not support it.As for ffmpeg, the filter was introduced in r7286814 which didn't make it into your build.Hence, you need to obtain an up-to-date version if you want to use the filter.Once installed, move -vf after -i, and run your command to get your results.$ ffmpeg -i somevideo.mp4  -vf select='gt(scene,0.9)' -vsync 0 -f image2 /tmp/thumbnails-%02d.jpg