[FFmpeg-user] How to drop every Nth frame?

[Stefano Sabatini]

On date Monday 2013-09-23 13:36:25 +0300, Andrey Aleksandrovich wrote:
> I also try:
> -filter:v select=mod'(n,372)',crop=in_w-20::11:,scale=320:240
> but it's the same
> 
> [Parsed_select_0 @ 0x543d35fc90] [Eval @ 0x3bd5b30b370] Missing ')' or
> too many args in 'mod(n'
> [Parsed_select_0 @ 0x543d35fc90] Error while parsing expression 'mod(n'
> [AVFilterGraph @ 0x543d2dfed0] Error initializing filter 'select' with
> args 'mod(n'

Please read and understand this:
http://ffmpeg.org/ffmpeg-filters.html#Notes-on-filtergraph-escaping

In this case you have to choose:
-filter:v "select='mod(n,372)',..."
or
-filter:v "select=mod(n\,372),..."

Also note the embedding double quotes required by the shell.

Also your crop syntax doesn't make sense (you're setting empty
expressions, please read crop documentation if you have doubts).