Correct ffmpeg output format argument

The pcm_f32le codec is only supported with the f32le output format.

src/audio/subprocess.rs

@@ -45,7 +45,7 @@ pub async fn ffmpeg_pcm(url: &str) -> Result<Box<dyn MediaSource + Send>, String
         .arg("-i")
         .arg(url)
         .arg("-f")
-        .arg("s16le")
+        .arg("f32le")
         .arg("-ar")
         .arg("48000")
         .arg("-ac")