Play videos in separate windows, syncing their time/seeking

[rieje]

I have multiple of the same videos but in different formats and found the best way to compare their quality is playing them in full screen, switching focus back and forth between the videos compared. Is it possible to control the time/seeking of these videos so they are in sync (ideally-frame-by-frame)? E.g. seeking 14 seconds ahead applies to all videos at the same time.

There's mpv --lavfi-complex='[vid1] [vid2] hstack [vo]' <vid1> --external-file=<vid2> but this is different because it only plays them side by side in one window. The differences in the quality of the videos are subtle and playing them fullscreen switching focus between the videos as they are playing is a much more efficient way to compare the quality of the videos visually.

[guidocella]

You can use lavfi-complex with fullscreen and --video-unscaled and cycle-values video-align-x -1 1.

[rieje]

This didn't do anything for me unless I zoomed out but then it just shifts the two videos left/right. I assume the intention was to swap the positions of the videos?

Also would an IPC server be able to sync the times of the videos as an alternative?

[guidocella]

Well video-unscaled works if the videos are the size of the screen, else you can adjust the zoom and alternate displaying the 2 videos by changing video-align. IPC sync woud be complicated.

[na-na-hi]

There is no need for separate windows for your use case. You can use --external-files option to add multiple videos as separate video tracks sharing the same timeline, then use _ to cycle through the video tracks. Time syncing is already handled in this case.