Experimental option to transcode surround sound audio to AC3 (#947)

## Description
Adds an experimental setting to prefer transcoding audio with more than
2 channels to AC3. Stereo audio does not transcode.

This is basically a workaround for HDMI ARC (not eARC) or optical audio
devices because instead of 2 uncompressed PCM channels, 6 AC3 channels
(ie 5.1) is possible.

An downside of enabling this is that embedded subtitles be burned in
causing a video transcode as well.

### Related issues
Fixes #255
Incorporates some code from #1410

### Testing
Just on the emulator so far to observe if the settings trigger the
transcode or not

## Screenshots
N/A

## AI or LLM usage
None

---------

Co-authored-by: darkflame91 <darkflame91@gmail.com>

app/src/main/java/com/github/damontecres/wholphin/preferences/AppPreference.kt

@@ -53,7 +53,10 @@ sealed interface AppPreference<Pref, T> {
         value: T?,
     ): String? = null
 
-    fun validate(value: T): PreferenceValidation = PreferenceValidation.Valid
+    fun validate(
+        prefs: Pref,
+        value: T,
+    ): PreferenceValidation = PreferenceValidation.Valid
 
     companion object {
         val SkipForward =
@@ -391,18 +394,25 @@ sealed interface AppPreference<Pref, T> {
                 defaultValue = true,
                 getter = { it.playbackPreferences.overrides.ac3Supported },
                 setter = { prefs, value ->
-                    prefs.updatePlaybackOverrides { ac3Supported = value }
+                    if (!value) prefs.updateExperimentalPreferences { preferAc3Surround = false }
+                    prefs.updatePlaybackOverrides {
+                        ac3Supported = value
+                    }
                 },
                 summaryOn = R.string.enabled,
                 summaryOff = R.string.disabled,
             )
+
         val DownMixStereo =
             AppSwitchPreference<AppPreferences>(
                 title = R.string.downmix_stereo,
                 defaultValue = false,
                 getter = { it.playbackPreferences.overrides.downmixStereo },
                 setter = { prefs, value ->
-                    prefs.updatePlaybackOverrides { downmixStereo = value }
+                    if (value) prefs.updateExperimentalPreferences { preferAc3Surround = false }
+                    prefs.updatePlaybackOverrides {
+                        downmixStereo = value
+                    }
                 },
                 summaryOn = R.string.enabled,
                 summaryOff = R.string.disabled,
@@ -1311,11 +1321,16 @@ data class AppSwitchPreference<Pref>(
     override val defaultValue: Boolean,
     override val getter: (prefs: Pref) -> Boolean,
     override val setter: (prefs: Pref, value: Boolean) -> Pref,
-    val validator: (value: Boolean) -> PreferenceValidation = { PreferenceValidation.Valid },
+    val validator: (prefs: Pref, value: Boolean) -> PreferenceValidation = { _, _ -> PreferenceValidation.Valid },
     @param:StringRes val summary: Int? = null,
     @param:StringRes val summaryOn: Int? = null,
     @param:StringRes val summaryOff: Int? = null,
 ) : AppPreference<Pref, Boolean> {
+    override fun validate(
+        prefs: Pref,
+        value: Boolean,
+    ): PreferenceValidation = validator.invoke(prefs, value)
+
     override fun summary(
         context: Context,
         value: Boolean?,

app/src/main/java/com/github/damontecres/wholphin/preferences/ExperimentalPreference.kt

@@ -4,6 +4,7 @@ import com.github.damontecres.wholphin.R
 import com.github.damontecres.wholphin.ui.nav.Destination
 import com.github.damontecres.wholphin.ui.preferences.PreferenceGroup
 import com.github.damontecres.wholphin.ui.preferences.PreferenceScreenOption
+import com.github.damontecres.wholphin.ui.preferences.PreferenceValidation
 
 object ExperimentalPreference {
     val Enable =
@@ -35,6 +36,30 @@ object ExperimentalPreference {
             summaryOn = R.string.enabled,
             summaryOff = R.string.disabled,
         )
+
+    val PreferAc3ForSurround =
+        AppSwitchPreference<AppPreferences>(
+            title = R.string.prefer_ac3_for_surround,
+            defaultValue = true,
+            getter = { it.experimentalPreferences.preferAc3Surround },
+            setter = { prefs, value ->
+                prefs.updateExperimentalPreferences {
+                    preferAc3Surround = value
+                }
+            },
+            summary = R.string.prefer_ac3_for_surround_summary,
+            validator = { prefs, value ->
+                prefs.playbackPreferences.overrides.let {
+                    if (value && !it.ac3Supported) {
+                        PreferenceValidation.Invalid("AC3 support is not enabled")
+                    } else if (value && it.downmixStereo) {
+                        PreferenceValidation.Invalid("Always downmixing to stereo")
+                    } else {
+                        PreferenceValidation.Valid
+                    }
+                }
+            },
+        )
 }
 
 val experimentalPreferences =
@@ -45,6 +70,7 @@ val experimentalPreferences =
                 preferences =
                     listOf(
                         ExperimentalPreference.VideoTunneling,
+                        ExperimentalPreference.PreferAc3ForSurround,
                     ),
             ),
         )