user36122: I borrowed an Apeman A87 and used it on a road trip. However, the audio came out apparently corrupted except sometimes when filming indoors and with the menu set to the default language of the market the camera was sold in -- i.e., in my case it was Italian, I set it to English because of the incomprehensible Italian translation, no audio, set it back to Italian, got some audio, switched it back to English, no audio again… except that I still got no audio when filming outside with the menu language set to Italian so that's probably not the culprit. Maybe. I don't know what to think anymore.
I had a look at the waveforms and the spectra and two things stand out in the corrupted tracks:

there are relatively large DC-biased sections at the beginning (and sometimes end) of the audio tracks which look to me like some kind of data blocks or markers, and
the rest of the tracks contain very high pitched noise, which also sounds like raw data interpreted as audio.

From one of the SD cards, I also retrieved a small file which reads like so:
$ file -k H264.1.TO.BS
H264.1.TO.BS: JVT NAL sequence, H.264 video @ L 51
- data

Anyway, I have two short examples here if anybody want to take a look. These come straight from the SD card, no re-encoding nor anything else.

https://andreafranceschini.org/files/apeman/nope.mov
https://andreafranceschini.org/files/apeman/ok.mov
https://andreafranceschini.org/files/apeman/H264.1.TO.BS

Any pointers appreciated :)

user24237: It's not an issue with the audio format.
Any player (VLC, ffplay) can decode the format because both videos have the same AAC LC Audio format:
Format            : AAC LC
Bit rate          : 128 kb/s
Channel(s)        : 2 channels
Channel layout    : L R
Sampling rate     : 48.0 kHz


36122: <p>I borrowed an Apeman A87 and used it on a road trip. However, the audio came out apparently corrupted except sometimes when filming indoors and with the menu set to the default language of the market the camera was sold in -- i.e., in my case it was Italian, I set it to English because of the incomprehensible Italian translation, no audio, set it back to Italian, got some audio, switched it back to English, no audio again… except that I still got no audio when filming outside with the menu language set to Italian so that's probably not the culprit. Maybe. I don't know what to think anymore.</p>
<p>I had a look at the waveforms and the spectra and two things stand out in the corrupted tracks:</p>
<ol>
<li>there are relatively large DC-biased sections at the beginning (and sometimes end) of the audio tracks which look to me like some kind of data blocks or markers, and</li>
<li>the rest of the tracks contain very high pitched noise, which also sounds like raw data interpreted as audio.</li>
</ol>
<p>From one of the SD cards, I also retrieved a small file which reads like so:</p>
<pre><code>$ file -k H264.1.TO.BS
H264.1.TO.BS: JVT NAL sequence, H.264 video @ L 51
- data
</code></pre>
<p>Anyway, I have two short examples here if anybody want to take a look. These come straight from the SD card, no re-encoding nor anything else.</p>
<ul>
<li><a href="https://andreafranceschini.org/files/apeman/nope.mov" rel="nofollow noreferrer">https://andreafranceschini.org/files/apeman/nope.mov</a></li>
<li><a href="https://andreafranceschini.org/files/apeman/ok.mov" rel="nofollow noreferrer">https://andreafranceschini.org/files/apeman/ok.mov</a></li>
<li><a href="https://andreafranceschini.org/files/apeman/H264.1.TO.BS" rel="nofollow noreferrer">https://andreafranceschini.org/files/apeman/H264.1.TO.BS</a></li>
</ul>
<p>Any pointers appreciated :)</p>
 24237: <p>It's not an issue with the audio format.</p>
<p>Any player (VLC, ffplay) can decode the format because both videos have the same <code>AAC LC</code> Audio format:</p>
<pre><code>Format            : AAC LC
Bit rate          : 128 kb/s
Channel(s)        : 2 channels
Channel layout    : L R
Sampling rate     : 48.0 kHz
</code></pre>
