mencoder vs. Canon EOS 500D video

-autosync <factor>
Gradually adjusts the A/V sync based on audio delay measurements. Specifying -autosync 0, the default, will cause frame timing to be based entirely on audio delay measurements. Specifying -autosync 1 will do the same, but will
subtly change the A/V correction algorithm. An uneven video framerate in a movie which plays fine with -nosound can often be helped by setting this to an integer value greater than 1. The higher the value, the closer the timing
will be to -nosound. Try -autosync 30 to smooth out problems with sound drivers which do not implement a perfect audio delay measurement. With this value, if large A/V sync offsets occur, they will only take about 1 or 2 sec-
onds to settle out. This delay in reaction time to sudden A/V offsets should be the only side-effect of turning this option on, for all sound drivers.