stream_wav: restore tweaks

QuasiBird still runs jittery at 22050 hz 16 bit stereo.
Mono is fine, and lower sample rates are fine too.

At max volume, so no volume scaling, the frame rate is quite high
but it still jitters. The question is why...

- does the buffer underrun?
- or does it spend too much time reading from SD card?
- or is the CPU busy?

Solutions:
- offload it to a different core
- do the I2S playback asynchronous

I guess it doesn't make sense tweaking this, as audio plays fine up to 48khz stereo
if no game is being played, just normal GUI updates.

internal_filesystem/lib/mpos/audio/stream_wav.py

@@ -144,7 +144,7 @@ def _scale_audio_powers_of_2(buf: ptr8, num_bytes: int, shift: int):
 class WAVStream:
     """
     WAV file playback stream with I2S output.
-    Supports 8/16/24/32-bit PCM, mono and stereo, auto-upsampling to >=22050 Hz.
+    Supports 8/16/24/32-bit PCM, mono and stereo, auto-upsampling to >=8000 Hz.
     """
 
     def __init__(
@@ -400,6 +400,8 @@ class WAVStream:
                 )
 
                 self._playback_rate = playback_rate
+		#ibuf = playback_rate # doesnt account for stereo vs mono...
+		ibuf = 32000
 
                 print(f"WAVStream: {original_rate} Hz, {bits_per_sample}-bit, {channels}-ch")
                 print(f"WAVStream: Playback at {playback_rate} Hz (factor {upsample_factor})")
@@ -425,7 +427,7 @@ class WAVStream:
                     print(
                         "WAVStream: I2S config: "
                         f"format={'MONO' if channels == 1 else 'STEREO'}, "
-                        f"ibuf={playback_rate}, has_sck={bool(self.i2s_pins.get('sck'))}, "
+                        f"ibuf={ibuf}, has_sck={bool(self.i2s_pins.get('sck'))}, "
                         f"mck_pin={self.i2s_pins.get('mck')}"
                     )
 
@@ -457,7 +459,7 @@ class WAVStream:
                             bits=16,
                             format=i2s_format,
                             rate=playback_rate,
-                            ibuf=playback_rate
+                            ibuf=ibuf
                         )
                     else:
                         self._i2s = machine.I2S(
@@ -468,7 +470,7 @@ class WAVStream:
                             bits=16,
                             format=i2s_format,
                             rate=playback_rate,
-                            ibuf=playback_rate
+                            ibuf=ibuf
                         )
                 except Exception as e:
                     print(f"WAVStream: I2S init failed: {e}")
@@ -482,8 +484,7 @@ class WAVStream:
                 # - Larger chunks = less overhead, smoother audio
                 # - The 0.5-second (stereo) or 1 second (mono) I2S buffer handles timing smoothness
                 bytes_per_second = original_rate * bytes_per_sample
-                chunk_size = int(bytes_per_second / 10)
-		# chunk_size of 8192 worked great with 22050hz stereo 16 bit so 88200 bytes per sample so fator 10.7
+                chunk_size = int(bytes_per_second / 10.7) # chunk_size of 8192 worked great with 22050hz stereo 16 bit so 88200 bytes per sample so fator 10.7
                 #chunk_size = bytes_per_second >> 3 # 12-14 fps
                 #chunk_size = bytes_per_second >> 4 # 16-18 fps but stutters
                 #chunk_size = int(bytes_per_second / 12) # 18 fps for 8khz mono, 16 fps for 22khz mono, higher stutters