[4.5.0] LOOP_BIDI seems to be non-functional

[Kinsie]

Quoting a teammate:

Quick check, does GZDoom no longer support bidirectional audio looping? LOOP_BIDI doesn't seem to work anymore and the LOOP_MIDI tag seems to be totally missing from the source code

[TheShadsy]

Hi, I'm the teammate! (also that was a typo, that should've said LOOP_BIDI, not MIDI)

But yes, I've noticed that LOOP_BIDI doesn't seem to be working when using A_StartSound with CHANF_LOOP. LOOP_START and LOOP_END are still honored, though. I tried this with both .ogg and .flac files and didn't notice any difference.

I've attached a sample sound with a LOOP_BIDI tag. It should be obvious that playback is being reversed, but the sound just restarts. Have I missed something, or is this feature having issues?

[Graf Zahl]

Loop_BIDI was an FModEx feature - it got removed along with that backend.

[Gez]

So it'd be up to chris to implement the functionality in OpenAL and then it could be restored?

[Chris]

IIRC, it wasn't a particularly cared-about feature, either in general for an audio library or for ZDoom itself. It could also pose a problem for a future enhancement I might do with OpenAL, that being direct ADPCM support in the mixer (it's a block-based adaptive codec that's nearly 4x smaller than 16-bit samples with relatively little quality loss, where samples depend on the decoder state from previous decoded samples; needing to read samples in reverse would create an obvious complication). A sound author that wants it could bake the reversed section into the sound and set the loop point on the backward and forward section to get the same effect.

[TheShadsy]

IIRC, it wasn't a particularly cared-about feature, either in general for an audio library or for ZDoom itself. It could also pose a problem for a future enhancement I might do with OpenAL, that being direct ADPCM support in the mixer (it's a block-based adaptive codec that's nearly 4x smaller than 16-bit samples with relatively little quality loss, where samples depend on the decoder state from previous decoded samples; needing to read samples in reverse would create an obvious complication). A sound author that wants it could bake the reversed section into the sound and set the loop point on the backward and forward section to get the same effect.

Somehow that hadn't even occurred to me, for whatever reason. That'll work; thanks for the clarification everyone!

And Gez, thank you for updating the wiki! I was just about to ask about that.

[Graf Zahl]

IIRC, it wasn't a particularly cared-about feature, either in general for an audio library or for ZDoom itself.

It obviously wasn't. It got removed along with FMod more than 3.5 years ago and this is the first time it ever came up.