sceAudiocodec: report the decoded size in bytes, not samples

The field at 0x24 is a byte count, like srcBytesRead next to it, and
sceAudiocodecGetOutputBytes describes the same quantity the same way (0x1200
for MPEG1 MP3). We were putting the sample count there, a quarter of the value,
and libmp3.prx takes it as the length of the PCM to pass on. Renamed to
dstBytesWritten so it reads like what it is.

Nothing on our side consumed the field, so this only changes what the firmware
modules see. mpeg.prx ignores it, which is why Atrac3+ playback was unaffected
either way, but libatrac3plus.prx does read it.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

Core/HLE/sceAudiocodec.cpp

@@ -398,7 +398,11 @@ static int sceAudiocodecDecode(u32 ctxPtr, int codec) {
 		}
 
 		ctx->srcBytesRead = inDataConsumed + headerBytes;
-		ctx->dstSamplesWritten = outSamples;
+		// In bytes, not samples. sceAudiocodecGetOutputBytes describes the same quantity in bytes
+		// (0x1200 for MPEG1 MP3), and libmp3.prx takes this as the length of the PCM to hand on -
+		// reporting the sample count instead gave it a quarter of every frame, which played back
+		// fast and metallic. The decoder always writes stereo 16-bit, whatever the source is.
+		ctx->dstBytesWritten = outSamples * 2 * (int)sizeof(int16_t);
 	}
 	return hleLogDebug(Log::ME, 0, "codec %s sampleRate: %d bytesPerFrame: %d channels: %d", GetCodecName(codec), sampleRate, bytesPerFrame, channels);
 }

Core/HLE/sceAudiocodec.h

@@ -50,7 +50,7 @@ struct SceAudiocodecCodec {
 	u32 inBuf;              // 0x18  the raw frame to decode
 	s32 srcBytesRead;       // 0x1c  written by the decoder
 	u32 outBuf;             // 0x20  where decoded PCM goes
-	s32 dstSamplesWritten;  // 0x24  written by the decoder
+	s32 dstBytesWritten;    // 0x24  written by the decoder, in bytes like srcBytesRead
 
 	// Codec-specific, 0x28..0x67.
 	union {