Audiobook player for KOReader

My Kobo Sage could technically do Bluetooth audio, but nothing on it could play an audiobook. This plugin fixes that: chaptered .m4b playback inside KOReader, so one small e-ink device covers both reading and listening.

The hard part was not the player, it was the radio. Kobo's stock software never initializes the Bluetooth chip for anything but its own narrow use, so the plugin brings the hardware up from a cold boot by itself: firing the rfkill GPIO, attaching the HCI transport with a bundled hciattach, and writing a stable Broadcom device address so pairings survive reboots. The address is captured once and kept in a small state file.

Audio comes from mpv, cross-compiled for the Kobo's ARM chip in KOReader's own toolchain container so the build is reproducible rather than a one-machine miracle. The result cold-starts, reconnects to headphones, remembers position per book, and handles chapter navigation from e-ink friendly controls.

What it demonstrates

Embedded Linux work several layers below where app development usually stops: GPIO, HCI transports, vendor firmware quirks, and cross-compilation. And the stubbornness to make owned hardware do what it was always capable of.