I originally tried this for a capture I did that was out of sync and it ended up making matters worse. The issue for me was my video and audio were using separ

I originally tried this for a capture I did that was out of sync and it ended up making matters worse. The issue for me was my video and audio were using separate clock sources on the capture end. This meant the streams started recording at different times AND drifted apart over time. Using a V4L2 capture device I finally managed to get something workable in ffmpeg by using the -ts flag with option 'asb' for both audio and video sources.