fix(player): show audio codec and bitrate in the performance overlay on ExoPlayer

The Android performance overlay showed only sample rate and channels for
EAC3, FLAC, DTS, TrueHD, and Opus tracks. The overlay reads the codec
from media3's Format.codecs, an RFC 6381 string only MP4/HLS provide
(hence AAC working), and the bitrate from Format.bitrate, which Matroska
carries only when the muxer wrote BPS statistics tags.

Fall back to the already-transmitted sample MIME type for the codec name
(audio and video), and measure the audio bitrate in the FFmpeg demuxer
from packet sizes over their pts span — the same source mpv uses for its
audio-bitrate property — when the container declares none.

close #2063

android/app/src/test/kotlin/com/edde746/plezy/exoplayer/StreamBitrateMeterTest.kt

@@ -0,0 +1,65 @@
+package com.edde746.plezy.exoplayer
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class StreamBitrateMeterTest {
+
+  /** Feeds [count] packets of [sizeBytes] every [intervalUs], starting at [startUs]. */
+  private fun StreamBitrateMeter.feed(count: Int, sizeBytes: Int, intervalUs: Long, startUs: Long = 0L) {
+    for (i in 0 until count) onPacket(startUs + i * intervalUs, sizeBytes)
+  }
+
+  @Test
+  fun `constant packet stream measures its bitrate`() {
+    val meter = StreamBitrateMeter()
+    // 1200-byte packets every 32 ms: 1200 * 8 / 0.032 = 300 kbps.
+    meter.feed(count = 32, sizeBytes = 1200, intervalUs = 32_000)
+    assertEquals(300_000, meter.bitrateBps())
+  }
+
+  @Test
+  fun `too few packets report nothing`() {
+    val meter = StreamBitrateMeter()
+    meter.feed(count = 15, sizeBytes = 1200, intervalUs = 32_000)
+    assertNull(meter.bitrateBps())
+  }
+
+  @Test
+  fun `zero pts span reports nothing`() {
+    val meter = StreamBitrateMeter()
+    repeat(32) { meter.onPacket(0L, 1200) }
+    assertNull(meter.bitrateBps())
+  }
+
+  @Test
+  fun `window drops old packets so a bitrate change is followed`() {
+    val meter = StreamBitrateMeter(windowUs = 1_000_000)
+    meter.feed(count = 100, sizeBytes = 1200, intervalUs = 32_000)
+    // Continue at four times the packet size; after well over a window of
+    // new packets, only the new rate remains.
+    meter.feed(count = 100, sizeBytes = 4800, intervalUs = 32_000, startUs = 100 * 32_000L)
+    assertEquals(1_200_000, meter.bitrateBps())
+  }
+
+  @Test
+  fun `backwards pts jump resets the window`() {
+    val meter = StreamBitrateMeter()
+    meter.feed(count = 32, sizeBytes = 1200, intervalUs = 32_000)
+    // Seek back: the single post-seek packet must not combine with the
+    // pre-seek span.
+    meter.onPacket(0L, 1200)
+    assertNull(meter.bitrateBps())
+    meter.feed(count = 31, sizeBytes = 1200, intervalUs = 32_000, startUs = 32_000)
+    assertEquals(300_000, meter.bitrateBps())
+  }
+
+  @Test
+  fun `empty packets are ignored`() {
+    val meter = StreamBitrateMeter()
+    meter.feed(count = 32, sizeBytes = 1200, intervalUs = 32_000)
+    meter.onPacket(32 * 32_000L, 0)
+    assertEquals(300_000, meter.bitrateBps())
+  }
+}