I created a .ac3 file containing 33 frames of silence (i.e. 1.376375 seconds) to later concat to the front of audio that was 33 frames early. set _DELAY33_=1.376375 set _SILENCE2_=anullsrc=channel_layout=2:sample_rate=48000 set _TARGET_=<path\name>.ac3 ffmpeg -y -f lavfi -i %_SILENCE2_% -t %_DELAY33_% -c ac3 "%_TARGET_%" I did get 33 frames of silence in a file. Good. But I also got these complaints: [out @ 0000000004a1a940] The "sample_fmts" option is deprecated: set the supported sample formats [out @ 0000000004a1a940] The "all_channel_counts" option is deprecated: accept all channel counts I did not use either of those deprecated options. And I do not understand the end of either complaint. Can anyone help? --Mark.