ALTCHA Adaptive CAPTCHA Audio Challenge doesn't work

Pause · Post by **Pause** » 2025-05-30, 15:13

Operating system: Windows 10
Browser version: 33.7.1
32-bit or 64-bit browser?: 64-bit
Problem URL: https://altcha.org/docs/v2/sentinel/fea ... e-captcha/
Browser theme (if not default): Default
Installed add-ons: N/A
Installed plugins: (about:plugins): N/A

If possible, please include the output of help->troubleshooting information (as text):

7 instances of this error happens from just loading the page:

These errors happen after trying to request an audio challenge:

As that page states, that is just a demo implementation of it (so it's the exact same challenge every time), but the audio challenge should still play as it does in other browsers.

It otherwise appears to solve as it should (as do the other checkbox versions on the main page of altcha.org, just doesn't play the audio challenge part of the 'Code Challenge' version which is also listed on the main page, but which I linked to the page only containing that one to prevent possible confusion).

Assuming that the demo is an accurate reflection of the actual hosted code of course, which I have no idea about whether that is the case.

I don't know whether anyone is using it or if anyone will in future, but I thought it's worth pointing out the issues Pale Moon has with it in case it does get popular*.

In case it helps to figure it out, they have a GitHub repo at https://github.com/altcha-org/altcha.

* The 'Sentinel' version which includes the audio challenge option is apparently part of a commercial license, not the underlying open source version which is much more limited according to this, this, and this.

Post by **vannilla** » 2025-05-30, 16:30

The widget appears to be loading a WAV file from the server inside a normal <audio> element.
I don't know how Pale Moon handles WAVs normally, on my system they are not played at all and visiting the file URL downloads the file, as it is normal for unsupported types.

Post by **Moonchild** » 2025-05-30, 16:54

The audio does "play" for me (i.e. there's no error thrown like for you, and it plays a 10 second sample) but it is silent when played back in the browser -- probably because their "wav" file format is 32-bit Signed Integer PCM; I don't think our PCM decoder understands that format (and it wouldn't make much sense for a captcha to use it -- that's a really high bit-resolution format for audio samples, wasting bandwidth... I don't think even professional audio equipment uses 32-bits PCM. For comparison, CD quality is 16-bit. I've seen 24-bit in some rare cases, and float is also fairly common, I think. but 32-bit int sample size?... no, I don't think so)

Pause · Post by **Pause** » 2025-05-30, 18:47

Glad that the reason could be figured out. I had no idea how to do so, so thank you for that.

I'll point it out to them and see what they say, as surely it's a good idea to not be wasteful with bandwidth (regardless of whether it's self-hosted) rather than it having to be implemented into the decoder (if it even can) if they're the only ones to use that one.

Pause · Post by **Pause** » 2025-05-31, 07:40

They agreed about the audio file parameters and said they'll adjust it and make sure it works with Pale Moon in the next release.

Post by **Moonchild** » 2025-05-31, 07:42

Pause wrote: ↑
2025-05-31, 07:40
They agreed about the audio file parameters and said they'll adjust it and make sure it works with Pale Moon in the next release.

Awesome news! Great to hear.

Pale Moon forum

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