Video playback synchronization

[atgeller]

Currently, with multiple camera angles, the different channels will begin playback at different times. Further, when playing the video frame-by-frame, cameras with different frame rates will quickly become quite out of sync. A broad and/or multifaceted video synchronization approach solving these issues would allow referees to rely on different angles representing different views at the same time (within a frame, so on the scale of <2 centiseconds).

[atgeller]

An easy strategy to solve the problem of recording/playback beginning at different times is using Barriers. This will lend a high degree of precision for the start points of videos from different channels will represent a highly similar real time. Unfortunately, one has to be careful with Barriers to avoid apparent deadlocks (an issue I'm running into with early experimentation).

For frame-by-frame mode, we could average the playback times of each channel, and then set each channel to that same average time. Given a high degree of precision for the start points (as above), this would likely result in errors no more than a frame or two, which should be sufficient precision.

[atgeller]

A further issue is that it's possible to select more cameras than are actually being used, which doesn't seem to be accounted for. In such instances, the barrier will never complete.

[alan-geller]

I think the simplest way to solve this problem might be to add a constraint and a feature:

• Only allow frame-by-frame if all cameras have the same frame rate. If we tell people in advance, they can easily arrange to get cameras that match in this way.
• Add a "super-slow-motion" option that's always available; say, 1% speed. This is pretty close to frame-by-frame.