Video Conversion Out of Synch Audio

[the-ether]

Hi guys,

I was trying to downsize a mkv file by re-enconding it using "ffmpeg -i file_video.mkv -c:v libx264 -b:v 1000k -c:a aac -b:a 128k output.mp4" but after running that the audio is out of synch (sometimes just stops for a few frames.). Is there anything I can do to fix the mp4?

Thanks guys.

[ProWo]

You should add the video framerate with -vf fps=24000/1001 (for 23.976, as example).

ffmpeg -i file_video.mkv -vf fps=24000/1001 -c:v libx264 -b:v 1000k -c:a aac -b:a 128k output.mp4

[the-ether]

You should add the video framerate with -vf fps=24000/1001 (for 23.976, as example).

ffmpeg -i file_video.mkv -vf fps=24000/1001 -c:v libx264 -b:v 1000k -c:a aac -b:a 128k output.mp4

It kind worked but I still get a delay when i fast forward the video. The audio is synched but it takes a few seconds to play (the audio. the video is working). It's like it takes a few seconds to catch up with the video.

[cholla]

You might try inserting one of these:
-c:a aac copy
-c:a aac -b:a 128k -strict -2
-c:a aac -b:a 128k -strict experimental

If that fails you could try :
-vsync -1
or
-async 1
Depending on which way the audio is out of sync.
Using ProWo's code with -vsync -1 &

ffmpeg -vsync -1 -i file_video.mkv -vf fps=24000/1001 -c:v libx264 -b:v 1000k -c:a aac copy output.mp4

You can also open the video in VLC & check what the amount of delay is by using the k or j keys.