@item -loop_output number_of_times
Repeatedly loop output for formats that support looping such as animated GIF
(0 will loop the output infinitely).
+@item -vsync parameter
+Video sync method. Video will be stretched/sqeezed to match the timestamps,
+it is done by duplicating and droping frames. With -map you can select from
+which stream the timestamps should be taken, you can leave either video or
+audio unchanged and sync the remaining stream(s) to the unchanged one.
+@item -async samples_per_second
+Audio sync method. "Stretches/sqeezes" the audio stream to match the timestamps,
+the parameter is the maximum samples per second by which the audio is changed.
+-async 1 is a special case where only the start of the audio stream is corrected
+without any later correction.
@end table
@node FFmpeg formula evaluator