Transcoding at lower bitrate for limited bandwidth (#58)

Hello!

To begin with, thanks a lot for Funkwhale and the Android application, which is delightful to use every day.

As mentioned in #58, the application does not yet have a way to reduce the amount of data exchanged between the player and the server. When streaming high-quality audio on 4G or 5G connection, it can get very costly if one does consume a lot of FLAC content. This PR is an attempt at solving this issue and is my first contribution to the project. I would appreciate some hints/helps according to unit tests, translations, and probably things I did not cover for the moment...

Here is a summary of what I have done:

• Add a new setting called "Bandwidth limitation" with an icon, and a basic description,
• If bandwidth limitation is set to limited, append &to=mp3&max_bitrate=320 to the listen URL of the candidate best track upload.

A better way to do it in the future would be to add a bar to configure the desired maximum bitrate, and probably check in the cache if the best upload is already there before asking for a reduced one. Testing that the best quality upload is already meeting the bandwidth constraint would be interesting to avoid an unneeded transcoding on the server side. I prefer to point out the flaws so that we can discuss about them together! 😄

Thank in advance,

Dylan

app/src/main/java/audio/funkwhale/ffa/model/Track.kt

@@ -67,11 +67,20 @@ data class Track(
   fun bestUpload(): Upload? {
     if (uploads.isEmpty()) return null
 
-    return when (PowerPreference.getDefaultFile().getString("media_cache_quality")) {
+    var bestUpload = when (PowerPreference.getDefaultFile().getString("media_cache_quality")) {
       "quality" -> uploads.maxByOrNull { it.bitrate } ?: uploads[0]
       "size" -> uploads.minByOrNull { it.bitrate } ?: uploads[0]
       else -> uploads.maxByOrNull { it.bitrate } ?: uploads[0]
     }
+
+    return when (PowerPreference.getDefaultFile().getString("bandwidth_limitation")) {
+      "unlimited" -> bestUpload
+      "limited" -> {
+        var listenUrl = bestUpload.listen_url
+        Upload(listenUrl.plus("&to=mp3&max_bitrate=320"), uploads[0].duration, 320_000)
+      }
+      else -> bestUpload
+    }
   }
 
   override fun cover(): String? {