[Feat] Support for third party equlizer

[eddyizm]

Discussed in #179

^{Originally posted by cmarcopolo October 17, 2025}
I use Poweramp equalizer and tempo is one of the few player that doesn´t seem to support a third party equalizer. I´ve been looking into this and found out that is only required to add a couple of lines to support. I know that there´s already an equalizer in the player but I find it limiting. I hope someone is able to add it. I would greatly apreciate it. I´m quoting from the support page of Poweramp equalizer:

Literally 2 lines of code required:

Send [AudioEffect.ACTION_OPEN_AUDIO_EFFECT_CONTROL_SESSION](https://developer.android.com/reference/android/media/audiofx/AudioEffect#ACTION_OPEN_AUDIO_EFFECT_CONTROL_SESSION) intent with the actual session id when playback starts
Send [AudioEffect.ACTION_CLOSE_AUDIO_EFFECT_CONTROL_SESSION](https://developer.android.com/reference/android/media/audiofx/AudioEffect#ACTION_CLOSE_AUDIO_EFFECT_CONTROL_SESSION) intent when playback ends

Additional hints:

don't change session id between played tracks, playlists, etc. Keep single session id per playback session (per playing service lifetime)
    this reduces possible artefacts on session start, as effects require some time to setup and apply
    also this approach reduces resources usage as no tear-down/re-setup of effects is required
don't use multiple session ids even if you use multiple MediaPlayers/AudioTracks (for example, for the crossfade)
    this also reduces resources usage as there is need for multiple effects then

To implement the hints above, get audio session id once from the first MediaPlayer/AudioTrack and reuse it for the next created MediaPlayers/AudioTracks.

Source

Thank you for your time, and for a great app.