fix: player crash when switching audio language (#89) - #129

Summary

Closes #89.

Fixes the player crash users reported when switching audio language from the track menu during playback. Also removes a second, related bug where switching audio from the D-pad handler path ran duplicated unsafe code.

Root cause

Two audio-track selection code paths in PlayerScreen.kt (the D-pad menu handler at ~line 1485 and the onSelectAudio callback at ~line 2075) built a TrackSelectionOverride(group, trackIndex) after only validating:

1. track.groupIndex < trackGroups.size ✓
2. group.type == TRACK_TYPE_AUDIO ✓
3. track.trackIndex < group.length ✗ missing

There was also no try/catch around exoPlayer.trackSelectionParameters = params.build().

AudioTrackInfo captures groupIndex / trackIndex at the moment onTracksChanged fires. Between that moment and the user actually picking a track from the menu (several seconds later, especially if they first opened the subtitles menu, browsed, then switched to audio), the player may have re-prepared due to:

• adaptive stream switch
• user switching source from the source picker
• MediaItem rebuild when a new external subtitle is selected
• automatic recovery from a transient network error

After any of those events the track groups layout can change, leaving the cached trackIndex out of bounds for the new group. Media3's TrackSelectionOverride constructor throws IllegalArgumentException and the crash propagates up to the Composable, tearing down the player.

Fix

Extracted the audio-track selection logic into a single private helper applyAudioTrackSelection(exoPlayer, track, audioTracks): Int? with proper defense:

private fun applyAudioTrackSelection(
    exoPlayer: ExoPlayer,
    track: AudioTrackInfo,
    audioTracks: List<AudioTrackInfo>
): Int? {
    return try {
        val params = exoPlayer.trackSelectionParameters.buildUpon()
            .clearOverridesOfType(C.TRACK_TYPE_AUDIO)
            .setPreferredAudioLanguage(track.language)

        val trackGroups = exoPlayer.currentTracks.groups
        val groupInRange = track.groupIndex in trackGroups.indices
        if (groupInRange) {
            val group = trackGroups[track.groupIndex]
            val isAudioGroup = group.type == C.TRACK_TYPE_AUDIO
            val trackInRange = track.trackIndex in 0 until group.length
            if (isAudioGroup && trackInRange) {
                params.setOverrideForType(
                    TrackSelectionOverride(group.mediaTrackGroup, track.trackIndex)
                )
            }
            // If stale, still apply setPreferredAudioLanguage so Media3 picks the
            // closest matching track on its own rather than crashing or leaving
            // the user on the wrong language.
        }

        exoPlayer.trackSelectionParameters = params.build()
        audioTracks.indexOfFirst { ... }.takeIf { it >= 0 } ?: track.index
    } catch (e: IllegalArgumentException) { ... null }
      catch (e: IllegalStateException) { ... null }
      catch (e: Exception) { ... null }
}

Key defensive additions:

1. Full try/catch around the whole block — the outer params.build() assignment could also throw on some devices when the player is in an invalid state.
2. clearOverridesOfType(C.TRACK_TYPE_AUDIO) first — stale overrides from prior selections no longer pin the player to a track index that may not exist in the new group layout.
3. trackIndex in 0 until group.length bounds check — this is the specific validation that was missing and caused the crash.
4. Graceful fallback — if the group/track validation fails, the setPreferredAudioLanguage hint still applies, so Media3 picks the closest matching track on its own rather than leaving the user on the wrong language.
5. Returns Int? — caller uses ?.let { selectedAudioIndex = it } so when the selection fails we keep the previous index rather than jumping to an incorrect one.

Both audio-selection call sites now shrink from ~20 lines to 3.

Not touched in this PR

The subtitle-selection paths at lines 934 and 983 already validate groupIndex in groups.indices and have been stable — they're left alone to keep the diff focused on the reported crash. They could be migrated to a similar helper in a follow-up if desired.

Risk

Low. The helper is strictly more defensive than the inlined code it replaces. In the normal case (fresh tracks, user picks immediately), behavior is identical. In the edge case (stale indices after re-prepare), the old code crashed and the new code either silently picks the correct track via language hint, or keeps the previous selection. Either is strictly better than a crash.