feat: infinite sources return Duration::MAX for total_duration

Previously, `total_duration()` returned `None` for both infinite and
unknown-duration sources, making them indistinguishable. Infinite
sources (generators, repeat, looped decoders, microphone) now return
`Some(Duration::MAX)`, so wrapping them with `TakeDuration` correctly
reports the requested duration instead of `None`.

Fixes #702

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Sim-hu

src/decoder/mod.rs

@@ -727,12 +727,11 @@ where
 
     /// Returns the total duration of this audio source.
     ///
-    /// Always returns `None` for looped decoders since they have no fixed end point -
-    /// they will continue playing indefinitely by seeking back to the start when reaching
-    /// the end of the audio data.
+    /// Always returns `Duration::MAX` for looped decoders since they play
+    /// indefinitely by seeking back to the start when reaching the end.
     #[inline]
     fn total_duration(&self) -> Option<Duration> {
-        None
+        Some(Duration::MAX)
     }
 
     /// Attempts to seek to a specific position in the audio stream.

src/microphone.rs

@@ -204,7 +204,7 @@ impl Source for Microphone {
     }
 
     fn total_duration(&self) -> Option<std::time::Duration> {
-        None
+        Some(std::time::Duration::MAX)
     }
 }
 
@@ -219,7 +219,7 @@ impl crate::FixedSource for Microphone {
     }
 
     fn total_duration(&self) -> Option<std::time::Duration> {
-        None
+        Some(std::time::Duration::MAX)
     }
 }
 

src/source/mod.rs

@@ -197,7 +197,10 @@ pub trait Source: Iterator<Item = Sample> {
 
     /// Returns the total duration of this source, if known.
     ///
-    /// `None` indicates at the same time "infinite" or "unknown".
+    /// `None` indicates that the duration is unknown. Infinite sources
+    /// (e.g. sine wave generators, repeating sources) return
+    /// `Some(Duration::MAX)` to distinguish them from sources with an
+    /// unknown but finite duration.
     fn total_duration(&self) -> Option<Duration>;
 
     /// Stores the source in a buffer in addition to returning it. This iterator can be cloned.

src/source/noise.rs

@@ -83,7 +83,7 @@ macro_rules! impl_noise_source {
             }
 
             fn total_duration(&self) -> Option<Duration> {
-                None
+                Some(Duration::MAX)
             }
 
             fn try_seek(&mut self, _pos: Duration) -> Result<(), crate::source::SeekError> {

src/source/repeat.rs

@@ -83,7 +83,7 @@ where
 
     #[inline]
     fn total_duration(&self) -> Option<Duration> {
-        None
+        Some(Duration::MAX)
     }
 
     #[inline]

src/source/sawtooth.rs

@@ -56,7 +56,7 @@ impl Source for SawtoothWave {
 
     #[inline]
     fn total_duration(&self) -> Option<Duration> {
-        None
+        Some(Duration::MAX)
     }
 
     #[inline]

src/source/signal_generator.rs

@@ -153,7 +153,7 @@ impl Source for SignalGenerator {
 
     #[inline]
     fn total_duration(&self) -> Option<Duration> {
-        None
+        Some(Duration::MAX)
     }
 
     #[inline]

src/source/sine.rs

@@ -56,7 +56,7 @@ impl Source for SineWave {
 
     #[inline]
     fn total_duration(&self) -> Option<Duration> {
-        None
+        Some(Duration::MAX)
     }
 
     #[inline]

src/source/square.rs

@@ -56,7 +56,7 @@ impl Source for SquareWave {
 
     #[inline]
     fn total_duration(&self) -> Option<Duration> {
-        None
+        Some(Duration::MAX)
     }
 
     #[inline]

src/source/take.rs

@@ -165,7 +165,7 @@ where
                 Some(self.requested_duration)
             }
         } else {
-            None
+            Some(self.requested_duration)
         }
     }