audio(mixer): SoundfileMixer doesn't resample files anymore

CHANGELOG.md

@@ -34,6 +34,10 @@ async def on_audio_data(processor, audio, sample_rate, num_channels):
 
 ### Changed
 
+- `SoundfileMixer` doesn't resample input files anymore to avoid startup
+  delays. The sample rate of the provided sound files now need to match the
+  sample rate of the output transport.
+
 - All input frames (text, audio, image, etc.) are now system frames. This means
   they are processed immediately by all processors instead of being queued
   internally.