h26x: replace Nalu's bitstream storage with Cow

This changes will enable the decoder to copy Nalu/Slice structs to internal
state instead of using Vec.

Addresses partially chromeos#49

Author: bgrzesik

examples/ccdec.rs

@@ -344,7 +344,7 @@ fn main() {
     let display = libva::Display::open().expect("failed to open libva display");
     let (mut decoder, frame_iter) = match args.input_format {
         EncodedFormat::H264 => {
-            let frame_iter = Box::new(NalIterator::<H264Nalu>::new(&input).map(Cow::Borrowed))
+            let frame_iter = Box::new(NalIterator::<H264Nalu>::new(&input))
                 as Box<dyn Iterator<Item = Cow<[u8]>>>;
 
             let decoder = Box::new(StatelessDecoder::<H264, _>::new_vaapi(
@@ -375,7 +375,7 @@ fn main() {
             (decoder, frame_iter)
         }
         EncodedFormat::H265 => {
-            let frame_iter = Box::new(NalIterator::<H265Nalu>::new(&input).map(Cow::Borrowed))
+            let frame_iter = Box::new(NalIterator::<H265Nalu>::new(&input))
                 as Box<dyn Iterator<Item = Cow<[u8]>>>;
 
             let decoder = Box::new(StatelessDecoder::<H265, _>::new_vaapi(

src/codec/h264/nalu.rs

@@ -4,6 +4,7 @@
 
 use anyhow::anyhow;
 use bytes::Buf;
+use std::borrow::Cow;
 use std::fmt::Debug;
 use std::io::Cursor;
 
@@ -22,7 +23,7 @@ pub struct Nalu<'a, U> {
     pub header: U,
     /// The mapping that backs this NALU. Possibly shared with the other NALUs
     /// in the Access Unit.
-    pub data: &'a [u8],
+    pub data: Cow<'a, [u8]>,
 
     pub size: usize,
     pub offset: usize,
@@ -80,7 +81,7 @@ where
 
         Ok(Nalu {
             header: hdr,
-            data: bitstream,
+            data: Cow::from(bitstream),
             size: nal_size,
             offset: nalu_offset,
             sc_offset: start_code_offset,

src/utils.rs

@@ -7,6 +7,7 @@
 //! This module is for anything that doesn't fit into the other top-level modules. Try not to add
 //! new code here unless it really doesn't belong anywhere else.
 
+use std::borrow::Cow;
 use std::io::Cursor;
 use std::io::Seek;
 use std::marker::PhantomData;
@@ -164,28 +165,40 @@ impl<'a, Nalu> NalIterator<'a, Nalu> {
 }
 
 impl<'a> Iterator for NalIterator<'a, H264Nalu<'a>> {
-    type Item = &'a [u8];
+    type Item = Cow<'a, [u8]>;
 
     fn next(&mut self) -> Option<Self::Item> {
         H264Nalu::next(&mut self.0)
             .map(|n| {
                 let start = n.sc_offset;
                 let end = n.offset + n.size;
-                &n.data[start..end]
+                match n.data {
+                    Cow::Borrowed(data) => Cow::Borrowed(&data[start..end]),
+                    Cow::Owned(mut data) => {
+                        data.truncate(end);
+                        Cow::Owned(data.split_off(start))
+                    }
+                }
             })
             .ok()
     }
 }
 
 impl<'a> Iterator for NalIterator<'a, H265Nalu<'a>> {
-    type Item = &'a [u8];
+    type Item = Cow<'a, [u8]>;
 
     fn next(&mut self) -> Option<Self::Item> {
         H265Nalu::next(&mut self.0)
             .map(|n| {
                 let start = n.sc_offset;
                 let end = n.offset + n.size;
-                &n.data[start..end]
+                match n.data {
+                    Cow::Borrowed(data) => Cow::Borrowed(&data[start..end]),
+                    Cow::Owned(mut data) => {
+                        data.truncate(end);
+                        Cow::Owned(data.split_off(start))
+                    }
+                }
             })
             .ok()
     }