refactor h264 depacketizer

* add a couple tests

* fix #4: put the whole video frame (including multiple NALs) into
  a single Bytes. This is simpler to use and speeds up the
  depacketize/h264_aac_writevideo benchmark. It's also a behavior
  change; now I include non-VUI data such as SPS/PPS/SEI into the
  data. I think this is a better default but it might be worth
  making customizable.

benches/depacketize.rs

@@ -3,7 +3,6 @@
 
 use std::num::NonZeroU16;
 
-use bytes::Buf;
 use criterion::{criterion_group, criterion_main, Criterion};
 use retina::client::{rtp::StrictSequenceChecker, Timeline};
 use retina::codec::{CodecItem, Depacketizer};
@@ -78,10 +77,7 @@ fn criterion_benchmark(c: &mut Criterion) {
                     CodecItem::VideoFrame(v) => v,
                     _ => return,
                 };
-                let mut slices = [std::io::IoSlice::new(b""); 2];
-                let n = v.chunks_vectored(&mut slices);
-                assert_eq!(n, 2);
-                assert_eq!(w.write_vectored(&slices[..]).unwrap(), v.remaining());
+                w.write_all(&v.data()[..]).unwrap();
             })
         })
     });

examples/client/mp4.rs

@@ -485,16 +485,16 @@ impl<W: AsyncWrite + AsyncSeek + Send + Unpin> Mp4Writer<W> {
         Ok(())
     }
 
-    async fn video(&mut self, mut frame: retina::codec::VideoFrame) -> Result<(), failure::Error> {
+    async fn video(&mut self, frame: retina::codec::VideoFrame) -> Result<(), failure::Error> {
         println!(
             "{}: {}-byte video frame",
             &frame.timestamp,
-            frame.remaining()
+            frame.data().remaining(),
         );
         if let Some(ref p) = frame.new_parameters {
             bail!("parameters change unimplemented. new parameters: {:#?}", p);
         }
-        let size = u32::try_from(frame.remaining())?;
+        let size = u32::try_from(frame.data().remaining())?;
         self.video_trak
             .add_sample(self.mdat_pos, size, frame.timestamp, frame.loss)?;
         self.mdat_pos = self
@@ -505,7 +505,8 @@ impl<W: AsyncWrite + AsyncSeek + Send + Unpin> Mp4Writer<W> {
             self.video_sync_sample_nums
                 .push(u32::try_from(self.video_trak.samples)?);
         }
-        write_all_buf(&mut self.inner, &mut frame).await?;
+        let mut data = frame.into_data();
+        write_all_buf(&mut self.inner, &mut data).await?;
         Ok(())
     }