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    #1

    System-wide audio/video sync issues ??

    Hi! Kubuntu 20.10 on an i7-4770k with an NVIDIA GeForce GTX 1060 (6GB) running the proprietary video drivers. I have a Scarlett USB audio interface, and I'm using jackd and running my system audio through it to the Scarlett.

    I've noticed that, system-wide, audio and video aren't quite synced right.

    I first noticed this while rendering out some videos in Windows 8 (same machine) -- in Windows the videos have perfect sync in the video editor, and when rendered the files have perfect sync, and videos played on youtube in a browser have perfect sync, etc.

    But when I boot into linux, the same mp4 files play a little out of sync, and so do videos on youtube. Estimating from experience sync'ing audio to video, the audio seems to come on the order of 10-30ms earlier than it should (or the video later, etc.)

    At first I thought "oh jackd must be buffering audio on the way out or something" but the audio is coming early compared to the video... Perhaps a setting in the NVIDIA control panels is causing the video frames to be buffered a little or something?

    Anything I can tweak or look in to to fix this? Thanks for any tips!
    Tags: audio, jackd, nvidia, sync, windows
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    #2
    Hmm, so I've been digging in to this a bit. I created a test file with single-frame flashes accompanied by a single-frame burst of noise. I play it (using vlc) and record the screen with my DSLR at 60fps (60/1.001), with a mic up against the speaker to remove time-of-travel.

    I did this in window and linux, and was surprised to find that window plays the sound about 3.5 frames late, and linux plays the sound about 3 frames early!

    I know that default OS operation is not designed for real-time scientific accuracy, but this is a spread of almost 110ms between the two, and I was somewhat dismayed to find that.

    There are lots of times I need to sync audio with video and don't have a clap to work with... I used to think I could do it by visual feel, but if I can't trust what I'm seeing I guess I can't. At least it explains the issues I was having... I was aligning the audio in windows (so it was actually early but played in sync) and then viewing in linux (where it now played 108ms early.)

    There's no chance this is a vlc bug, is there?

    Here's the demo file in case anyone wants to try: http://caseyconnor.org/pub/video/noise.mp4
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