Sound time correction like subtitles

[calinb]

Audio delay is a very important feature (ideally expressed in msec, positive and negative). While you are correct that sync problems are the fault of the video, it is often quite difficult to obtain perfect sync in a video, for a number of reasons. This is especially true when encoding mpeg2 transport streams. Sometimes sync problems may be fixed by remuxing the video, as you've noted, but how much does the audio need to change?

When I have a sync problem in one of my encodings, I use MPC as a tool to find new delay values. First I must find the correct delay offset by watching a section of the video near the beginning. I adjust and note the audio delay (+ / -) that's required to correct the sync. Hopefully, an audio delay will be all that's necessary to achieve perfect sync, but I must also check a section near the end of the video to see if an audio "stretch" is required. If an additional delay adjustment is necessary to achieve A/V sync near the end of the video, I must attempt to "stretch" the sound to fit the video so it remains in sync. Again, I need to know the numbers--(timestamp in the video and delay required) so I may calculate the percentage of time stretch required.

Finally, I can remux with mkvmerge with a delay and stretch value to correct the sync.

If I mis-calculate, or if I have a video that that has audio or video errors in a few sections due to capture errors, it's nice to be able to adjust the sync during playback too.

Audio delay is a very important feature to many users! Please consider adding it to BSPlayer.

BTW, I would argue that subtitle sync problems are also the fault of the video ;)