decoder: enable fully dynamic StatelessVideoDecoder trait objects

Add the necessary implementations and wrapper types to allow a
StatelessVideoDecoder to be turned into a fully dynamic trait object
with no other dependency that its Descriptor.

This now allows user code to control any instance of a decoder,
regardless of its codec or backend, through the same code path.

examples/ccdec.rs

@@ -6,7 +6,6 @@
 //! input and writing the raw decoded frames to a file.
 
 use std::borrow::Cow;
-use std::cell::RefCell;
 use std::ffi::OsStr;
 use std::fs::File;
 use std::io::Cursor;
@@ -16,11 +15,9 @@ use std::os::fd::AsFd;
 use std::os::fd::BorrowedFd;
 use std::path::Path;
 use std::path::PathBuf;
-use std::rc::Rc;
 use std::str::FromStr;
 
 use argh::FromArgs;
-use cros_codecs::backend::vaapi::decoder::VaapiDecodedHandle;
 use cros_codecs::codec::h264::parser::Nalu as H264Nalu;
 use cros_codecs::codec::h265::parser::Nalu as H265Nalu;
 use cros_codecs::decoder::stateless::av1::Av1;
@@ -32,6 +29,7 @@ use cros_codecs::decoder::stateless::StatelessDecoder;
 use cros_codecs::decoder::stateless::StatelessVideoDecoder;
 use cros_codecs::decoder::BlockingMode;
 use cros_codecs::decoder::DecodedHandle;
+use cros_codecs::decoder::DynDecodedHandle;
 use cros_codecs::decoder::StreamInfo;
 use cros_codecs::multiple_desc_type;
 use cros_codecs::utils::simple_playback_loop;
@@ -342,51 +340,54 @@ fn main() {
     };
 
     let display = libva::Display::open().expect("failed to open libva display");
+
+    // The created `decoder` is turned into a `DynStatelessVideoDecoder` trait object. This allows
+    // the same code to control the decoder no matter what codec or backend we are using.
     let (mut decoder, frame_iter) = match args.input_format {
         EncodedFormat::H264 => {
             let frame_iter = Box::new(NalIterator::<H264Nalu>::new(&input))
                 as Box<dyn Iterator<Item = Cow<[u8]>>>;
 
-            let decoder =
-                Box::new(StatelessDecoder::<H264, _>::new_vaapi(display, blocking_mode).unwrap())
-                    as Box<dyn StatelessVideoDecoder<Handle = _, FramePool = _>>;
+            let decoder = StatelessDecoder::<H264, _>::new_vaapi(display, blocking_mode)
+                .unwrap()
+                .into_trait_object();
 
             (decoder, frame_iter)
         }
         EncodedFormat::VP8 => {
             let frame_iter = create_vpx_frame_iterator(&input);
 
-            let decoder =
-                Box::new(StatelessDecoder::<Vp8, _>::new_vaapi(display, blocking_mode).unwrap())
-                    as Box<dyn StatelessVideoDecoder<Handle = _, FramePool = _>>;
+            let decoder = StatelessDecoder::<Vp8, _>::new_vaapi(display, blocking_mode)
+                .unwrap()
+                .into_trait_object();
 
             (decoder, frame_iter)
         }
         EncodedFormat::VP9 => {
             let frame_iter = create_vpx_frame_iterator(&input);
 
-            let decoder =
-                Box::new(StatelessDecoder::<Vp9, _>::new_vaapi(display, blocking_mode).unwrap())
-                    as Box<dyn StatelessVideoDecoder<Handle = _, FramePool = _>>;
+            let decoder = StatelessDecoder::<Vp9, _>::new_vaapi(display, blocking_mode)
+                .unwrap()
+                .into_trait_object();
 
             (decoder, frame_iter)
         }
         EncodedFormat::H265 => {
             let frame_iter = Box::new(NalIterator::<H265Nalu>::new(&input))
                 as Box<dyn Iterator<Item = Cow<[u8]>>>;
 
-            let decoder =
-                Box::new(StatelessDecoder::<H265, _>::new_vaapi(display, blocking_mode).unwrap())
-                    as Box<dyn StatelessVideoDecoder<Handle = _, FramePool = _>>;
+            let decoder = StatelessDecoder::<H265, _>::new_vaapi(display, blocking_mode)
+                .unwrap()
+                .into_trait_object();
 
             (decoder, frame_iter)
         }
         EncodedFormat::AV1 => {
             let frame_iter = create_vpx_frame_iterator(&input);
 
-            let decoder =
-                Box::new(StatelessDecoder::<Av1, _>::new_vaapi(display, blocking_mode).unwrap())
-                    as Box<dyn StatelessVideoDecoder<Handle = _, FramePool = _>>;
+            let decoder = StatelessDecoder::<Av1, _>::new_vaapi(display, blocking_mode)
+                .unwrap()
+                .into_trait_object();
 
             (decoder, frame_iter)
         }
@@ -395,7 +396,7 @@ fn main() {
     let mut md5_context = md5::Context::new();
     let mut output_filename_idx = 0;
 
-    let mut on_new_frame = |handle: Rc<RefCell<VaapiDecodedHandle<BufferDescriptor>>>| {
+    let mut on_new_frame = |handle: DynDecodedHandle<BufferDescriptor>| {
         if args.output.is_some() || args.compute_md5.is_some() {
             handle.sync().unwrap();
             let picture = handle.dyn_picture();

src/decoder.rs

@@ -151,6 +151,45 @@ pub trait DecodedHandle {
     fn resource(&self) -> std::cell::Ref<Self::Descriptor>;
 }
 
+/// Implementation for any boxed [`DecodedHandle`], including trait objects.
+impl<H> DecodedHandle for Box<H>
+where
+    H: DecodedHandle + ?Sized,
+{
+    type Descriptor = H::Descriptor;
+
+    fn dyn_picture<'a>(&'a self) -> Box<dyn DynHandle + 'a> {
+        self.as_ref().dyn_picture()
+    }
+
+    fn timestamp(&self) -> u64 {
+        self.as_ref().timestamp()
+    }
+
+    fn coded_resolution(&self) -> Resolution {
+        self.as_ref().coded_resolution()
+    }
+
+    fn display_resolution(&self) -> Resolution {
+        self.as_ref().display_resolution()
+    }
+
+    fn is_ready(&self) -> bool {
+        self.as_ref().is_ready()
+    }
+
+    fn sync(&self) -> anyhow::Result<()> {
+        self.as_ref().sync()
+    }
+
+    fn resource(&self) -> std::cell::Ref<Self::Descriptor> {
+        self.as_ref().resource()
+    }
+}
+
+/// Trait object for [`DecodedHandle`]s using a specific `Descriptor`.
+pub type DynDecodedHandle<D> = Box<dyn DecodedHandle<Descriptor = D>>;
+
 /// A queue where decoding jobs wait until they are completed, at which point they can be
 /// retrieved.
 struct ReadyFramesQueue<T> {

src/decoder/stateless.rs

@@ -32,6 +32,7 @@ use crate::decoder::BlockingMode;
 use crate::decoder::DecodedHandle;
 use crate::decoder::DecoderEvent;
 use crate::decoder::DecoderFormatNegotiator;
+use crate::decoder::DynDecodedHandle;
 use crate::decoder::FramePool;
 use crate::decoder::ReadyFramesQueue;
 use crate::decoder::StreamInfo;
@@ -285,8 +286,78 @@ pub trait StatelessVideoDecoder {
     /// Returns a file descriptor that signals `POLLIN` whenever an event is pending on this
     /// decoder.
     fn poll_fd(&self) -> BorrowedFd;
+
+    /// Transforms the decoder into a [`StatelessVideoDecoder`] trait object.
+    ///
+    /// All decoders going through this method present the same virtual interface when they return.
+    /// This is useful in order avoid monomorphization of application code that can control
+    /// decoders using various codecs or backends.
+    fn into_trait_object(
+        self,
+    ) -> DynStatelessVideoDecoder<<Self::Handle as DecodedHandle>::Descriptor>
+    where
+        Self: Sized + 'static,
+        Self::FramePool: Sized + 'static,
+        Self::Handle: 'static,
+    {
+        Box::new(DynStatelessVideoDecoderWrapper(self))
+    }
+}
+
+/// Wrapper type for a `StatelessVideoDecoder` that can be turned into a trait object with a common
+/// interface.
+struct DynStatelessVideoDecoderWrapper<D: StatelessVideoDecoder>(D);
+
+impl<D> StatelessVideoDecoder for DynStatelessVideoDecoderWrapper<D>
+where
+    D: StatelessVideoDecoder,
+    <D as StatelessVideoDecoder>::FramePool: Sized + 'static,
+    <D as StatelessVideoDecoder>::Handle: 'static,
+{
+    type Handle = DynDecodedHandle<<D::Handle as DecodedHandle>::Descriptor>;
+    type FramePool = dyn FramePool<Descriptor = <D::FramePool as FramePool>::Descriptor>;
+
+    fn decode(&mut self, timestamp: u64, bitstream: &[u8]) -> Result<usize, DecodeError> {
+        self.0.decode(timestamp, bitstream)
+    }
+
+    fn flush(&mut self) -> Result<(), DecodeError> {
+        self.0.flush()
+    }
+
+    fn frame_pool(&mut self, layer: PoolLayer) -> Vec<&mut Self::FramePool> {
+        self.0
+            .frame_pool(layer)
+            .into_iter()
+            .map(|p| p as &mut Self::FramePool)
+            .collect()
+    }
+
+    fn stream_info(&self) -> Option<&StreamInfo> {
+        self.0.stream_info()
+    }
+
+    fn next_event(&mut self) -> Option<DecoderEvent<Self::Handle>> {
+        self.0.next_event().map(|e| match e {
+            DecoderEvent::FrameReady(h) => {
+                DecoderEvent::FrameReady(Box::new(h) as DynDecodedHandle<_>)
+            }
+            DecoderEvent::FormatChanged(_n) => todo!(),
+        })
+    }
+
+    fn poll_fd(&self) -> BorrowedFd {
+        self.0.poll_fd()
+    }
 }
 
+pub type DynStatelessVideoDecoder<D> = Box<
+    dyn StatelessVideoDecoder<
+        Handle = DynDecodedHandle<D>,
+        FramePool = dyn FramePool<Descriptor = D>,
+    >,
+>;
+
 pub trait StatelessCodec {
     /// Type providing current format information for the codec: resolution, color format, etc.
     ///
@@ -453,9 +524,9 @@ where
 
 #[cfg(test)]
 pub(crate) mod tests {
-    use crate::decoder::stateless::StatelessDecoderBackend;
     use crate::decoder::stateless::StatelessVideoDecoder;
     use crate::decoder::DecodedHandle;
+    use crate::decoder::FramePool;
 
     /// Stream that can be used in tests, along with the CRC32 of all of its frames.
     pub struct TestStream {
@@ -474,16 +545,17 @@ pub(crate) mod tests {
     ///
     /// `dump_yuv` will dump all the decoded frames into `/tmp/framexxx.yuv`. Set this to true in
     /// order to debug the output of the test.
-    pub fn test_decode_stream<D, B, L>(
+    pub fn test_decode_stream<D, H, FP, L>(
         decoding_loop: L,
         mut decoder: D,
         test: &TestStream,
         check_crcs: bool,
         dump_yuv: bool,
     ) where
-        B: StatelessDecoderBackend,
-        D: StatelessVideoDecoder<Handle = B::Handle, FramePool = B::FramePool>,
-        L: Fn(&mut D, &[u8], &mut dyn FnMut(B::Handle)) -> anyhow::Result<()>,
+        H: DecodedHandle,
+        FP: FramePool,
+        D: StatelessVideoDecoder<Handle = H, FramePool = FP>,
+        L: Fn(&mut D, &[u8], &mut dyn FnMut(H)) -> anyhow::Result<()>,
     {
         let mut crcs = test.crcs.lines().enumerate();
 

src/utils.rs

@@ -287,7 +287,7 @@ pub fn simple_playback_loop<D, R, I, H, FP>(
 ) -> anyhow::Result<()>
 where
     H: DecodedHandle,
-    FP: FramePool<Descriptor = H::Descriptor>,
+    FP: FramePool<Descriptor = H::Descriptor> + ?Sized,
     D: StatelessVideoDecoder<Handle = H, FramePool = FP> + ?Sized,
     R: AsRef<[u8]>,
     I: Iterator<Item = R>,