diff --git a/app/Tests/Settings/TranscriptionOpusBitrateTests.cs b/app/Tests/Settings/TranscriptionOpusBitrateTests.cs
new file mode 100644
index 00000000..33a75682
--- /dev/null
+++ b/app/Tests/Settings/TranscriptionOpusBitrateTests.cs
@@ -0,0 +1,54 @@
+using AIStudio.Settings.DataModel;
+
+namespace AIStudio.Tests.Settings;
+
+///
+/// Checks which bitrate the transcription pipeline ends up asking the Opus encoder for.
+///
+///
+/// This number is the whole reason the setting exists. Until v26.9.1 the encoder was fixed at
+/// 32 kbps, and transcription models silently dropped what had been spoken quietly -- a greeting at
+/// the start of a recording never reached the transcript. Two ways back to that value have to stay
+/// closed: the arm catching a bitrate nobody declared, and the member a settings file the app cannot
+/// read falls back to. Both are one edit away from pointing at the lowest quality again.
+///
+[TestFixture]
+public sealed class TranscriptionOpusBitrateTests
+{
+ private static readonly Dictionary EXPECTED_BITS_PER_SECOND = new()
+ {
+ [TranscriptionOpusBitrate.KBPS_32] = 32_000,
+ [TranscriptionOpusBitrate.KBPS_64] = 64_000,
+ [TranscriptionOpusBitrate.KBPS_128] = 128_000,
+ [TranscriptionOpusBitrate.KBPS_256] = 256_000,
+ };
+
+ [Test]
+ public void EveryOfferedBitrateAsksForWhatItsNameSays()
+ {
+ foreach (var bitrate in Enum.GetValues())
+ {
+ Assert.That(EXPECTED_BITS_PER_SECOND.ContainsKey(bitrate), Is.True, $"The selection offers {bitrate}, so this test has to state what that is worth in bits per second.");
+ Assert.That(bitrate.GetBitsPerSecond(), Is.EqualTo(EXPECTED_BITS_PER_SECOND[bitrate]), $"{bitrate} is what the user picked; anything else travels to the encoder behind their back.");
+ }
+ }
+
+ [Test]
+ public void ABitrateNobodyDeclaredFallsBackToTheRecommendedOne()
+ {
+ var undeclared = (TranscriptionOpusBitrate)999;
+
+ Assert.That(Enum.IsDefined(undeclared), Is.False, "The point of this test is a value outside the enum; a declared one would prove nothing.");
+ Assert.That(undeclared.GetBitsPerSecond(), Is.EqualTo(128_000u), "Not knowing which quality was meant is no reason to pick the worst one available.");
+ }
+
+ [Test]
+ public void AnUnreadableSettingsValueLandsOnTheRecommendedBitrate()
+ {
+ //
+ // TolerantEnumConverter answers a value it cannot parse with the member whose underlying
+ // value is zero. Which member that is decides what a damaged settings file transcribes with:
+ //
+ Assert.That(default(TranscriptionOpusBitrate), Is.EqualTo(TranscriptionOpusBitrate.KBPS_128), "The member with the underlying value zero is what a settings file the app cannot read falls back to, so it has to be the recommended bitrate.");
+ }
+}
\ No newline at end of file
diff --git a/runtime/src/media.rs b/runtime/src/media.rs
index d41282f9..1378fe7d 100644
--- a/runtime/src/media.rs
+++ b/runtime/src/media.rs
@@ -1835,6 +1835,30 @@ mod tests {
let _ = fs::remove_dir_all(directory);
}
+ /// Verifies the requested bitrate reaches the encoder rather than a fixed one.
+ #[test]
+ fn the_requested_bitrate_reaches_the_opus_encoder() {
+ let directory = std::env::temp_dir().join(format!("ai-studio-media-test-{}", rand::random::()));
+ fs::create_dir_all(&directory).unwrap();
+ let input = directory.join("input.wav");
+ fs::write(&input, wav_noise(OUTPUT_SAMPLE_RATE, OUTPUT_SAMPLE_RATE)).unwrap();
+
+ let mut sizes = Vec::new();
+ for bitrate in [32_000u32, 256_000] {
+ let output = directory.join(format!("output-{bitrate}.webm"));
+ let result = normalize_media(&input, &output, DEFAULT_MAX_PASS_THROUGH_BYTES, bitrate, &MediaJob::new()).unwrap();
+ assert!(!result.pass_through);
+ sizes.push(fs::metadata(&output).unwrap().len());
+ }
+
+ // One second of noise cannot be squeezed into a comparable size at both ends of the scale,
+ // so the higher bitrate has to produce a markedly larger file. Two outputs of roughly equal
+ // size would mean the requested bitrate never arrived and the encoder kept its own:
+ assert!(sizes[1] > sizes[0] * 2, "the higher bitrate did not grow the output: {sizes:?}");
+
+ let _ = fs::remove_dir_all(directory);
+ }
+
/// Verifies cancellation removes both final and partial outputs.
#[test]
fn cancellation_does_not_leave_an_output_file() {
@@ -1962,7 +1986,28 @@ mod tests {
/// Constructs a minimal mono 16-bit PCM WAV containing one constant sample value.
fn wav_constant(sample_rate: u32, samples: u32, sample: i16) -> Vec {
- let data_size = samples * 2;
+ wav_samples(sample_rate, &vec![sample; samples as usize])
+ }
+
+ /// Constructs a minimal mono 16-bit PCM WAV filled with deterministic pseudo-random noise.
+ ///
+ /// Noise is what a bitrate can be measured with: it barely compresses, so the encoder has to
+ /// spend whatever it was given on it. A tone would not do -- variable bitrate encodes one at
+ /// nearly the same size no matter which target it was asked for.
+ fn wav_noise(sample_rate: u32, samples: u32) -> Vec {
+ let mut state = 0x2545_F491_4F6C_DD1Du64;
+ let mut noise = Vec::with_capacity(samples as usize);
+ for _ in 0..samples {
+ state = state.wrapping_mul(6_364_136_223_846_793_005).wrapping_add(1_442_695_040_888_963_407);
+ noise.push((state >> 48) as i16);
+ }
+
+ wav_samples(sample_rate, &noise)
+ }
+
+ /// Wraps mono 16-bit PCM samples in a minimal WAV container.
+ fn wav_samples(sample_rate: u32, samples: &[i16]) -> Vec {
+ let data_size = samples.len() as u32 * 2;
let mut wav = Vec::with_capacity(44 + data_size as usize);
wav.extend_from_slice(b"RIFF");
wav.extend_from_slice(&(36 + data_size).to_le_bytes());
@@ -1976,7 +2021,7 @@ mod tests {
wav.extend_from_slice(&16u16.to_le_bytes());
wav.extend_from_slice(b"data");
wav.extend_from_slice(&data_size.to_le_bytes());
- for _ in 0..samples {
+ for sample in samples {
wav.extend_from_slice(&sample.to_le_bytes());
}
wav