Unified Stream trait: read() and write() on one type

Stream trait: read() returns PesFrame, write() accepts PesFrame.
A stream is a stream — you read from it or write to it.
No separate Input/Output traits.

API: libfreemkv::input(url) and libfreemkv::output(url, title, codecs)
Returns Box<dyn Stream>.

src/mux/iso.rs

@@ -256,8 +256,8 @@ impl IsoStream {
     }
 }
 
-impl crate::pes::InputStream for IsoStream {
-    fn next_frame(&mut self) -> io::Result<Option<crate::pes::PesFrame>> {
+impl crate::pes::Stream for IsoStream {
+    fn read(&mut self) -> io::Result<Option<crate::pes::PesFrame>> {
         // Return buffered frame
         if let Some(frame) = self.pending_frames.pop_front() {
             return Ok(Some(frame));
@@ -301,6 +301,12 @@ impl crate::pes::InputStream for IsoStream {
         }
     }
 
+    fn write(&mut self, _frame: &crate::pes::PesFrame) -> io::Result<()> {
+        Err(io::Error::new(io::ErrorKind::Unsupported, "ISO is read-only for PES"))
+    }
+
+    fn finish(&mut self) -> io::Result<()> { Ok(()) }
+
     fn info(&self) -> &crate::disc::DiscTitle {
         &self.disc_title
     }