codec: introduce Parameters

As of ffmpeg 3.1, a new `AVCodecParameters` type and related API introduced.
This commit contains minimal changes to support new API.

examples/transcode-audio.rs

@@ -47,10 +47,12 @@ struct Transcoder {
 
 fn transcoder<P: AsRef<Path>>(ictx: &mut format::context::Input, octx: &mut format::context::Output, path: &P, filter_spec: &str) -> Result<Transcoder, ffmpeg::Error> {
 	let input   = ictx.streams().best(media::Type::Audio).expect("could not find best audio stream");
-	let decoder = try!(input.codec().decoder().audio());
+	let mut decoder = try!(input.codec().decoder().audio());
 	let codec   = try!(ffmpeg::encoder::find(octx.format().codec(path, media::Type::Audio)).expect("failed to find encoder").audio());
 	let global  = octx.format().flags().contains(ffmpeg::format::flag::GLOBAL_HEADER);
 
+	try!(decoder.set_parameters(input.codec_parameters()));
+
 	let mut output  = try!(octx.add_stream(codec));
 	let mut encoder = try!(output.codec().encoder().audio());
 
@@ -73,6 +75,8 @@ fn transcoder<P: AsRef<Path>>(ictx: &mut format::context::Input, octx: &mut form
 	output.set_time_base((1, decoder.rate() as i32));
 
 	let encoder = try!(encoder.open_as(codec));
+	try!(output.set_codec_parameters_from(&encoder));
+
 	let filter  = try!(filter(filter_spec, &decoder, &encoder));
 
 	Ok(Transcoder {

src/codec/context.rs

@@ -4,8 +4,8 @@ use std::rc::Rc;
 use libc::c_int;
 use ffi::*;
 use ::media;
-use ::Codec;
-use super::{Flags, Id, Debug, Compliance, threading};
+use ::{Codec, Error};
+use super::{Flags, Id, Debug, Compliance, threading, Parameters};
 use super::decoder::Decoder;
 use super::encoder::Encoder;
 
@@ -103,6 +103,15 @@ impl Context {
 			}
 		}
 	}
+
+	pub fn set_parameters(&mut self, params: &Parameters) -> Result<(), Error> {
+		unsafe {
+			match avcodec_parameters_to_context(self.as_mut_ptr(), params.as_ptr()) {
+				e if e < 0 => Err(Error::from(e)),
+				_          => Ok(()),
+			}
+		}
+	}
 }
 
 impl Drop for Context {

src/codec/mod.rs

@@ -20,6 +20,9 @@ pub use self::capabilities::Capabilities;
 
 pub mod codec;
 
+pub mod parameters;
+pub use self::parameters::Parameters;
+
 pub mod video;
 pub use self::video::Video;
 

src/codec/parameters.rs

@@ -0,0 +1,57 @@
+use std::rc::Rc;
+
+use ffi::*;
+
+pub struct Parameters {
+	ptr:   *mut AVCodecParameters,
+	owner: Option<Rc<Drop>>,
+}
+
+unsafe impl Send for Parameters { }
+
+impl Parameters {
+	pub unsafe fn wrap(ptr: *mut AVCodecParameters, owner: Option<Rc<Drop>>) -> Self {
+		Parameters { ptr: ptr, owner: owner }
+	}
+
+	pub unsafe fn as_ptr(&self) -> *const AVCodecParameters {
+		self.ptr as *const _
+	}
+
+	pub unsafe fn as_mut_ptr(&mut self) -> *mut AVCodecParameters {
+		self.ptr
+	}
+}
+
+impl Parameters {
+	pub fn new() -> Self {
+		unsafe {
+			Parameters { ptr: avcodec_parameters_alloc(), owner: None }
+		}
+	}
+}
+
+impl Drop for Parameters {
+	fn drop(&mut self) {
+		unsafe {
+			if self.owner.is_none() {
+				avcodec_parameters_free(&mut self.as_mut_ptr());
+			}
+		}
+	}
+}
+
+impl Clone for Parameters {
+	fn clone(&self) -> Self {
+		let mut ctx = Parameters::new();
+		ctx.clone_from(self);
+
+		ctx
+	}
+
+	fn clone_from(&mut self, source: &Self) {
+		unsafe {
+			avcodec_parameters_copy(self.as_mut_ptr(), source.as_ptr());
+		}
+	}
+}

src/format/stream/stream.rs

@@ -27,6 +27,12 @@ impl<'a> Stream<'a> {
 		}
 	}
 
+	pub fn codec_parameters(&self) -> codec::Parameters {
+		unsafe {
+			codec::Parameters::wrap((*self.as_ptr()).codecpar, Some(self.context.destructor()))
+		}
+	}
+
 	pub fn index(&self) -> usize {
 		unsafe {
 			(*self.as_ptr()).index as usize

src/format/stream/stream_mut.rs

@@ -2,7 +2,7 @@ use std::ops::Deref;
 use std::mem;
 
 use ffi::*;
-use ::Rational;
+use ::{Rational, Error};
 use super::Stream;
 use format::context::common::Context;
 
@@ -40,6 +40,15 @@ impl<'a> StreamMut<'a> {
 			av_stream_set_r_frame_rate(self.as_mut_ptr(), value.into().into());
 		}
 	}
+
+	pub fn set_codec_parameters_from(&mut self, context: &::codec::Context) -> Result<(), Error> {
+		unsafe {
+			match avcodec_parameters_from_context((*self.as_mut_ptr()).codecpar, context.as_ptr()) {
+				e if e < 0 => Err(Error::from(e)),
+				_          => Ok(()),
+			}
+		}
+	}
 }
 
 impl<'a> Deref for StreamMut<'a> {