Add ChannelLayout API (#38)

* Create channel_layout directory

* Rename ChannelLayout -> ChannelLayoutMask

* Add enum Channel (<-> AVChannel)

* Add struct ChannelCustom (<-> AVChannelCustom)

* Add enum ChannelOrder (<-> AVChannelOrder)

* Add struct ChannelLayout

- Smart copy-on-write pointer to AVChannelLayout
- idiomatic Rust API wrapping around FFmpeg APIs
- no Ambisonic support (yet)
- consts will need to be manually updated

* Add ChannelLayoutIter (iterator over all standard layouts)

* Add codec/Audio::ch_layouts

* Add ch_layout API to Audio-related structs

src/codec/decoder/audio.rs

@@ -12,7 +12,10 @@ use crate::frame;
 use crate::util::format;
 #[cfg(not(feature = "ffmpeg_5_0"))]
 use crate::{packet, Error};
-use crate::{AudioService, ChannelLayout};
+use crate::{AudioService, ChannelLayoutMask};
+
+#[cfg(feature = "ffmpeg_5_1")]
+use crate::ChannelLayout;
 
 pub struct Audio(pub Opened);
 
@@ -69,22 +72,34 @@ impl Audio {
         unsafe { (*self.as_ptr()).block_align as usize }
     }
 
-    pub fn channel_layout(&self) -> ChannelLayout {
-        unsafe { ChannelLayout::from_bits_truncate((*self.as_ptr()).channel_layout) }
+    pub fn channel_layout(&self) -> ChannelLayoutMask {
+        unsafe { ChannelLayoutMask::from_bits_truncate((*self.as_ptr()).channel_layout) }
     }
 
-    pub fn set_channel_layout(&mut self, value: ChannelLayout) {
+    pub fn set_channel_layout(&mut self, value: ChannelLayoutMask) {
         unsafe {
             (*self.as_mut_ptr()).channel_layout = value.bits();
         }
     }
 
-    pub fn request_channel_layout(&mut self, value: ChannelLayout) {
+    pub fn request_channel_layout(&mut self, value: ChannelLayoutMask) {
         unsafe {
             (*self.as_mut_ptr()).request_channel_layout = value.bits();
         }
     }
 
+    #[cfg(feature = "ffmpeg_5_1")]
+    pub fn ch_layout(&self) -> ChannelLayout {
+        unsafe { ChannelLayout::from(&self.as_ptr().as_ref().unwrap().ch_layout) }
+    }
+
+    #[cfg(feature = "ffmpeg_5_1")]
+    pub fn set_ch_layout(&mut self, value: ChannelLayout) {
+        unsafe {
+            self.as_mut_ptr().as_mut().unwrap().ch_layout = value.into_owned();
+        }
+    }
+
     pub fn audio_service(&mut self) -> AudioService {
         unsafe { AudioService::from((*self.as_mut_ptr()).audio_service_type) }
     }