libobs,obs-ffmpeg: Add option for recording lossless audio

[derrod]

Description

Adds support for manually selecting the recording audio encoder in the UI.

Currently adds 16, 24, and 32 bit PCM as well as 24-bit ALAC and 16-bit FLAC (their respective default bit-depths in FFmpeg's order of formats).

Screenshot (note: out of date, minor changes with RFC 45, but overall still the same UX):

#8498 adds the necessary UI to prevent users from selecting invalid container and audio codec combinations.

Motivation and Context

Lossless audio recording is a highly requested feature (e.g. ideas page posts 271, 1342, 1680, and probably many more) due to the additional flexibility in editing and avoidance of generational loss.

Additionally, PCM floating point audio allows for some additional flexibility when it comes to editing and fixing of audio in post, as clipping audio (i.e. >1.0f or <-1.0f) is retained and can be adjusted down to no longer be clipping. Aside from being able to make up for wrong recording levels in editing, this is also useful in situations where constructive interference resulted in the final output clipping while individually sources were fine (this currently happens invisibly due to the lack of a master mixer).

How Has This Been Tested?

Recorded some videos.

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.

[TianQiBuTian]

Crash on open settings.
Log: https://obsproject.com/logs/OwXxp9HwmUE0BRiz
Crash log: https://obsproject.com/logs/fkiO7swIjOTcfcJs

[derrod]

Crash on open settings. Log: https://obsproject.com/logs/OwXxp9HwmUE0BRiz Crash log: https://obsproject.com/logs/fkiO7swIjOTcfcJs

I believe this was due to no default config entry for AudioEncoder being set, this should be fixed now.

[derrod]

One thing that is left to be done (ignoring conflicts with #8090) is a compatibility check.

Right now we have the following situation:

Containers	AAC	ALAC	FLAC	Opus	PCM
FLV	✅	❌	❌	❌	❌
MP4	✅	✅	✅1	✅1	❌2
MOV	✅	✅	❌	❌	✅
MKV	✅	✅	✅	✅	✅
M3U8 (HLS)	✅	❌	❌	✅	❌
TS	✅	❌	❌	✅	❌

The following issues are worth noting:

• MP4 with FLAC crashes Resolve but seems to work fine in other software
• MKV support in editors remains poor
• This was not tested with UI: Add fragmented MP4/MOV formats #7276

Edit: I've listed all valid audio, video, and container combinations with this PR here: https://github.com/derrod/obs-studio/wiki/Container-Codec-Support

Footnotes

1. Current obs-deps FFmpeg version requires "experimental" standards compliance (-strict -2), no longer necessary in latest FFmpeg ↩ ↩²

2. Support is standardised, but FFmpeg doesn't support it yet. See https://trac.ffmpeg.org/ticket/10185 ↩

[derrod]

Drafting until RFC 45 stuff (especially #8090) is merged so it can be rebased and adjusted to those changes (if they make it into 29.1, otherwise I'd prefer if we can get this in first).

Edit: On second thought, let's leave it open in case 45-5 needs more time.

[alialkhatib]

I don't have anything to contribute except that I'm very excited about this. i've been recording audio separately to get 32-bit floating point audio from my audio interface (zoom f3), so this would simplify my recording setup pretty dramatically. thank you so much for doing the legwork on this

[derrod]

Updated to split out FFmpeg and PCM32 into their own commits to make them easier to skip. I'm personally not entirely sold on keeping FLAC around. Support for it in MP4 seems bad in editing software and we already have ALAC anyway.
Perhaps one of the PCM variants could also be removed, lthough compatibility is of course great there.

Also added a compatibility error message in case a non-supported combination of codec and container is chosen:

In my testing I've found that with multiple audio tracks you can get stuck on starting the recording, but #8175 fixes that.

[TianQiBuTian]

Can you add FLAC 24-bit format?
Because FLAC supports 24-bits, and some websites need at least 24-bits to enable the Hi-Res option.

[tytan652]

Just a couple of nitpik.

[derrod]

Rebased now that RFC 45 PRs have been merged, still requires #8496 and ideally should be considered with #8498 to communicate to users what is and isn't compatible.

[pkviet]

LGTM, thought it would take more code.

[derrod]

As @flaeri noted this will also prevent people from (having to) use Custom FFmpeg output for these features and reduce support requests related to it. So I'm hoping we can squeeze this into 29.1 together with #8498.

[RytoEX]

Seemed fine at a glance.