itch.io

When the camera angle changes, the bitrate goes way up, so it could either be a disk I/O performance bottleneck or a decoder maximum bitrate bottleneck.

I'm assuming that the APK content is the same as what's in the desktop edition.  If so:

• VP9 isn't even supported in hardware prior to about 2015 or so, and probably not consistently even then. Devices without hardware VP9 support won't be able to decode it except on the CPU. For higher bit rates, that's likely to stutter badly (not to mention eating the battery).
• The relatively high maximum bitrate of 12 Mbps might be a problem for devices with high write count on the flash, which causes read performance to slow down. Or you could be hitting hardware decoder performance bottlenecks from having too many I-frames or something. Either way, the official Android recommendations for VP9 bitrate from Google are just 2.6 megabits per second maximum bitrate for streaming content at 1080p, and you're at almost 5 times that.

Recompressing the content with more modest codec settings should help. Try H.264 main profile (or even baseline profile) for 1080p30 content with 8 bits per color channel, with a maximum bitrate to somewhere around 1.5–4 megabits per second.

It is also possible that VP9 is supported broadly enough at a more modest bitrate that nobody will complain about it, so you might try building two APKs — one with VP9 and one with H.264, both capped at 4 Mbps or so — and see which one works better for the folks who are having trouble.