Changes between Version 49 and Version 50 of FilteringGuide

Timestamp:

Nov 28, 2019, 11:59:28 AM (7 years ago)

Author:

slhck

Comment:

add sendcmd examples

FilteringGuide

@@ -187 +187 @@
 There are other options for generating synthetic video input, see [http://stackoverflow.com/questions/11640458/how-can-i-generate-a-video-file-directly-from-an-ffmpeg-filter-with-no-actual-in here] and [http://stackoverflow.com/a/15795112/32453 here] ("generic equation" filter).
 
+== Scripting Filters from a File ==
+
+Suppose you want to change some filter parameters based on an input file. Some filters support the option to receive commands via [https://ffmpeg.org/ffmpeg-filters.html#sendcmd_002c-asendcmd `sendcmd`]. Run `ffmpeg -filters` and check the `C` column – if it is present, a filter supports receiving input this way.
+
+For example, if you want to rotate the input at seconds 0, 1, and 2, create a file called `cmd.txt` with the content:
+
+{{{
+0 rotate angle '45*PI/180';
+1 rotate angle '90*PI/180';
+2 rotate angle '180*PI/180';
+}}}
+
+Now run an example stream:
+
+{{{
+ffmpeg -f lavfi -i testsrc -filter_complex "[0:v]sendcmd=f=cmd.txt,rotate" -f matroska - | ffplay -
+}}}
+
+Some examples of this technique can be seen [https://stackoverflow.com/a/49600924/435093 here].
+
 == Other Filter Examples ==