I have a 50 fps PAL video in MKV format. I know you can add multiple audio streams in MKV, so I've extracted/converted the audio from a NTSC 29.970 fps video; because it's in the language that I want, to AC3 and added the file to the MKV. As it's to be expected the audio doesn't match. The audio I'm trying to add is about 4 minutes longer than the original, probably because of the 50 fps, and it eventually gets out of sync. Someone suggested a program called AC3to, which is supposed to help me sync and convert the 29.970 fps audio to 50 fps audio. Most of the AC3to tutorials I've found online, help people fix audio/video sync issues when the fps are not that far off... 29.970 fps to 30 fps, 29.970 fps to 24 fps etc. But 29.970 fps to 50 fps is a huge difference. I successfully ran the audio through AC3to, but it results in a Chipmunk effect, very fast audio. Is it even possible to sync the audio from a 29.970 fps video after extraction, to a 50 fps video?. I'm going to post the thread in the audio and video conversion section because I don't even know if it's an audio problem of a video issue.