Possible bug in 5.1 encoding

[bmcfee]

Hey folks, I've been banging my head against a transcoding issue with 5.1 multichannel recordings, and I'm reasonably sure that it's down to an error in either oggenc or libvorbis. TLDR is that the last channel (surround-right) is corrupted.

I'm working with the following recording: https://freesound.org/people/Bokir26/sounds/383922/ but other recordings from different sources (eg https://freesound.org/people/ToXXuS/sounds/591235/ ) demonstrate the same behavior.

I first noticed the erroneous behavior when using sox to convert:

sox 383922__bokir26__commuter-train-03-traffic-jakarta-indonesia.wav 383922__bokir26__commuter-train-03-traffic-jakarta-indonesia.ogg

and the behavior replicates when using oggenc directly, both with version 1.4.0 (provided by ubuntu) and 1.4.2 (built locally from source):

oggenc 383922__bokir26__commuter-train-03-traffic-jakarta-indonesia.wav -o 383922__bokir26__commuter-train-03-traffic-jakarta-indonesia.ogg

I've also tried working directly from raw format and explicitly setting the channels/rate/bit depth, but no luck there as well.

For comparison purposes, here are spectrogram plots of the original channel 5 and that produced by oggenc:

And as a baseline, channel 0 looks as follows:

Channels 0-4 (front left/right/center + LFE + surround-left) all seem unaffected, so it seems unlikely to be some kind of byte-ordering or interleaving bug.

Flac encoding via sox does work fine (all channels preserved), so I don't believe there are any problems with the input audio.

Additionally, if I discard the last channel when transcoding (using sox [infile] [outfile] remix 1 2 3 4 5) everything works as expected. Similarly, if I skip a channel (eg discard the LFE channel 4: sox [infile] [outfile] remix 1 2 3 5 6), there is no corruption. It seems to be a fundamental issue with generating more than 5 channels: replicating channel 1 6 times (remix 1 1 1 1 1 1) triggers the error, but only on the last channel: the first five are preserved.

(Yes, I know this is not the sox repository: I'm only using sox to easily generate test cases that break things in controlled ways.)

Anyone have a hunch about what's going on here?

[bmcfee]

Quick follow-up: it also works fine if I add an empty seventh channel (?!) remix 1 2 3 4 5 6 0. (Or replace 0 by 1-6 to mix all channels as a seventh output). There seems to be something magically wrong with 6-channel output.

[xiphmont]

Currently on the road, but wanted to let you know that I saw the message and will be looking into it quickly. Of you don't hear back from me by tomorrow, feel free to pester incessantly. Monty

…

On Wed, Dec 1, 2021, 13:16 Brian McFee ***@***.***> wrote: Quick follow-up: it also works fine if I add an empty seventh channel (?!) remix 1 2 3 4 5 6 0. (Or replace 0 by 1-6 to mix all channels as a seventh output). There seems to be something magically wrong with 6-channel output. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#30 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACWMHEGGZC3ZMJOZ474URYDUOZQ65ANCNFSM5JFEAX4A> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

[bmcfee]

I don't at all want to pester incessantly 😁 but am checking in to see if there's any update / confirmation of this one?

[bmcfee]

Hey, just checking back to see if there's been any progress on confirming this?

[bmcfee]

Checking in again to see if anyone's been able to confirm or update this one?