Hybrid Replay Buffer

[derrod]

Description

Implements replay buffer using the Hybrid MP4/MOV muxer instead of FFmpeg.

Motivation and Context

• Feature parity with FFmpeg output
• Consistency between recording/replay buffer
• New features!

This implements a second hotkey as often requested (e.g. on Fider) that will dump the contents of the buffer after saving so two replay buffers saved back to back do not contain the same content¹

How Has This Been Tested?

Tested locally with both hotkeys and HEVC.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

Footnotes

1. Currently saving is allowed on non-keyframes, and discarding only happens up until the last keyframe. So there can be a few seconds of overlap still. ↩

[Warchamp7]

The additional hotkey option was my proposal in lieu of a checkbox so I'm fine with this on the UX front.

[derrod]

Fixed up a rebase whoopsie that broke the build. Should be g2g now.

[exeldro]

Would it be much work to support multi track video for the replay buffer?

[derrod]

Would it be much work to support multi track video for the replay buffer?

Mh, does it not work? I suppose there might be some nuance with how purging the buffer works that could result in tracks not starting at the same time.

[exeldro]

The "mp4_replay_buffer" output does not have the multi track video flag set, so I would think it does not work, but I have not tried it yet.

[derrod]

The "mp4_replay_buffer" output does not have the multi track video flag set, so I would think it does not work, but I have not tried it yet.

Ah I see, adding that part would be trivial for sure. I would be concerned about sync, since the DTS of keyframes can vary across tracks if b-frames are in use. I'd probably have to add a check to find the IDR on the primary track and then work forwards/backwards to find them for all the other tracks as well to determine a safe cutoff point.

In revisiting the code I also noticed that it just hardcodes a single flag (MP4_USE_NEGATIVE_CTS) which is technically valid but we'd probably want to reuse whatever is set for the primary output here too.

[derrod]

Updated with the following:

• Added OBS_OUTPUT_MULTI_TRACK_AV flag since that should work more or less fine, but let's call it experimental
• Added MOV replay buffer (this PR predates Hybrid MOV being merged so it didn't have it)
• Ensured that flags in muxer_settings are parsed and passed-through to replay mux thread

[chewybluff]

Is it supposed to work in current state? With hybrid mov/mp4 both hotkeys to save replay produce 0kb files and no info in logs, i've tried some artifact builds a while ago, and now built from source

[derrod]

Is it supposed to work in current state? With hybrid mov/mp4 both hotkeys to save replay produce 0kb files and no info in logs, i've tried some artifact builds a while ago, and now built from source

It seems there was a typo that made its way in during one of the rebases or something. It should be fixed now.

[chewybluff]

The file is being saved now, though there is no "replay buffer saved to" message in obs window and log. Sadly, no overshoot fixes here

[derrod]

The file is being saved now, though there is no "replay buffer saved to" message in obs window and log. Sadly, no overshoot fixes here

What do you mean by "overshoot"?

[chewybluff]

The file is being saved now, though there is no "replay buffer saved to" message in obs window and log. Sadly, no overshoot fixes here

What do you mean by "overshoot"?

Overlapping content from previous replay

[Fenrirthviti]

There's nothing to fix there, that is how the replay buffer is currently designed.

We are open to the idea of improving the replay buffer, but it's a finnicky feature that needs care and hasn't been a priority. It's well outside scope of this PR, and not related.

[derrod]

The file is being saved now, though there is no "replay buffer saved to" message in obs window and log. Sadly, no overshoot fixes here

What do you mean by "overshoot"?

Overlapping content from previous replay

If you have a short keyframe interval and use the discard hotkey the overlap will be short. But it's somewhat unavoidable unless we implement a delay that waits until the next keyframe to do a clean cut (similar to how file splitting works). But if the encoder is configured with a very long keyframe interval it could take a long time for the replay to be able to save.