Split

Per-app audio focus for rooted Android, with a WebUI button in KernelSU.

Music keeps playing over a game.
Any app can be switched back to normal behaviour.
Turn the whole thing off and it is genuinely off.

No companion app, no Xposed, no hooks. One module, one app-op, and a button on the module card in the KernelSU manager.

---

What v2 fixes

v1 set TAKE_AUDIO_FOCUS to ignore on every installed package and reverted with default. On HyperOS default is not stock. The platform rejects the focus request and logs:

W/AS.HardeningEnforcer: AudioHardening focus request for req 1 ignored
                        for com.spotify.music (10302), level: partial
W/AS.AudioService:      Audio focus request blocked by hardening

With v1 installed, every app sat in that state. Measured effect:

• Focus stack permanently empty: no app could ever own audio.
• Blocked apps retried every 5 seconds, indefinitely — thousands of rejected binder calls into system_server per day.
• Disabling the module changed nothing, because restore() wrote default, which was the exact state that was already broken.

Verified on device: setting a package to allow stops the retry loop instantly and puts it back in the focus stack with gain=GAIN.

So v2 never writes default. Only two values:

Value	Meaning
allow	app takes focus normally and can pause others (stock behaviour)
ignore	app never takes focus, so it plays over others (overlay)

---

What v2.0.2 fixes

If every tap in the WebUI answers Failed, this is why, and this is what changed.

The engine lived at /data/adb/split/splitctl, and only customize.sh ever put it there — once, at install time. A hot reinstall runs the old uninstall.sh first, and that script deletes /data/adb/split outright. The incoming module then had hotinstall.sh guarding itself with:

[ -x "$DIR/splitctl" ] || exit 0

so it quietly did nothing. End state: module files present, engine gone, every WebUI action exec'ing a binary that does not exist (exit 127), surfaced to the user as the single word "Failed".

v2.0.2 removes the dependency instead of documenting it:

• splitctl provision redeploys the engine from the module directory. Idempotent.
• customize.sh, service.sh, hotinstall.sh and the WebUI all run it first.
• The WebUI prepends a bootstrap to every ksu.exec, so a wiped state directory heals on the next tap even before the boot service has run.
• Failures report the reason — Failed: appops rejected ... — instead of "Failed".
• set applies to the device before writing config, and returns a non-zero exit code when appops rejects it. Config can no longer claim a state the device refused.

---

The WebUI

Tap WebUI on the Split card in the KernelSU manager. There is no IP to look up and no port to remember: the page runs inside the manager and talks to the module through KernelSU's own ksu.exec bridge.

• Master switch: on applies your rules, off returns every app to allow.
• Per app: Normal or Overlay, one tap, applied immediately.
• Search: filters 400+ packages by name or label.
• Reset all: clears every rule and restores normal focus everywhere.

A browser build is also served for desktop use, at http://<device-ip>:<port>. The port is chosen at boot and stored in /data/adb/split/port; if 8080 is taken it walks up to 8092 automatically instead of failing. splitctl serve prints the port it settled on.

Config lives in /data/adb/split/, outside the module directory, so it survives reboots, module updates and even disabling the module.

/data/adb/split/config.tsv    pkg<TAB>ignore, one per line
/data/adb/split/enabled       1 or 0
/data/adb/split/applied.txt   what is currently set to ignore
/data/adb/split/port          chosen automatically, or pin your own
/data/adb/split/bind          optional, default 0.0.0.0

---

Install

1. Root with KernelSU or Magisk.
2. Flash Split-Module-v2.0.2.zip.
3. Reboot.
4. Tap WebUI on the module card.

The module touches no system files, so it also works as a hot install where the manager supports it.

The browser UI needs BusyBox; KernelSU and Magisk both ship one and the service checks /data/adb/ksu/bin/busybox, /data/adb/magisk/busybox and $PATH. The KernelSU WebUI needs nothing extra.

---

Command line

su -c /data/adb/split/splitctl status
su -c /data/adb/split/splitctl provision  # redeploy the engine, idempotent
su -c '/data/adb/split/splitctl set com.spotify.music ignore'
su -c '/data/adb/split/splitctl set com.spotify.music allow'
su -c /data/adb/split/splitctl disable      # everything back to allow
su -c /data/adb/split/splitctl enable       # re-apply saved rules
su -c /data/adb/split/splitctl serve        # start the browser UI, prints port
su -c /data/adb/split/splitctl restore-all  # nuclear: allow on every package

restore-all is slow by nature: one appops write per installed package, roughly a minute for ~450 packages. restore only touches packages Split has changed, so it is near instant.

---

Revert

Disable the module and reboot. The watchdog at /data/adb/service.d/split-watchdog.sh sees the module disabled or removed and runs splitctl restore, which sets every changed package back to allow.

By hand, any time:

su -c /data/adb/split/splitctl disable

Uninstalling does the same, then deletes /data/adb/split and the watchdog.

---

Debugging

# what does the op actually say?
su -c 'cmd appops get com.spotify.music TAKE_AUDIO_FOCUS'

# who owns audio right now?
su -c 'dumpsys audio | grep -A6 "Audio Focus stack"'

# is anything still being blocked? these lines should stop appearing
su -c 'dumpsys audio | grep AudioHardening | tail'

# which port did the browser UI end up on?
su -c 'cat /data/adb/split/port'

Reading the result:

Symptom	Meaning
ignore, app plays over others	working as configured
allow, app pauses when another starts	stock behaviour, working
default	broken state: run splitctl apply
AudioHardening ... ignored repeating	that package is not at allow
WebUI says Failed	engine missing from /data/adb/split (run splitctl provision), or appops rejected the package; the toast now names the reason
WebUI button missing	module not enabled, or webroot/ missing from the module dir
Browser UI does not load	BusyBox missing, or ps -A | grep httpd is empty

---

Compatibility

Tested on:

• Xiaomi Pad 8 Pro (HyperOS, Android 16), where the default behaviour above was measured
• Xiaomi Pad 7 Ultra, Xiaomi Pad 7
• Poco X7 Pro, Redmi 10 Pro Max

The default-is-not-stock quirk is HyperOS-specific. On other ROMs default may well behave like stock; v2 avoids it either way, so behaviour is the same everywhere.

Requires KernelSU or Magisk.

---

Building

No compiler step.

Linux / macOS / Termux

cd module && zip -r ../Split-Module-v2.0.2.zip . -x '.*'

Windows

./build.ps1

Requirements:

• LF line endings on every script (customize.sh, service.sh, bin/splitctl, www/cgi-bin/api, hotinstall.sh, update-binary). CRLF silently breaks the shebang.
• Forward slashes in zip entry names. Compress-Archive writes backslashes and produces a zip Android cannot extract; build.ps1 builds entries by hand.
• META-INF/com/google/android/update-binary must stay in the archive.
• webroot/ must be named exactly that and contain index.html. Do not set permissions on it: KernelSU applies its own ownership and SELinux context.

Layout

module/
  module.prop                 identity and version
  customize.sh                install-time setup, watchdog, hot install
  service.sh                  boot: apply rules, start the browser UI
  hotinstall.sh               run right after a hot install
  uninstall.sh                restore, stop server, clean up
  bin/splitctl                provision | apply | restore | restore-all | set |
                              enable | disable | serve | status
  webroot/index.html          the KernelSU WebUI
  www/index.html              same page, served over HTTP
  www/cgi-bin/api             JSON API behind it
  META-INF/.../update-binary  KernelSU/Magisk installer

License

MIT.