codec: improve encoder state transitions

This commit improves the state transitions for the `codec::*` structs as
discussed in #7.

src/codec/encoder/audio.rs

@@ -1,29 +1,56 @@
 use std::ops::{Deref, DerefMut};
+use std::ptr;
 
 use libc::c_int;
 use ffi::*;
 
-use super::Encoder;
-use ::{Packet, Error};
+use super::Encoder as Super;
+use ::{Packet, Error, Dictionary, Codec};
 use ::frame;
 
-pub struct Audio(pub Encoder);
+pub struct Audio(pub Super);
 
 impl Audio {
-	pub fn encode(&mut self, frame: &frame::Audio, out: &mut Packet) -> Result<bool, Error> {
+	pub fn open(mut self) -> Result<Encoder, Error> {
 		unsafe {
-			let mut got: c_int = 0;
+			match avcodec_open2(self.as_mut_ptr(), ptr::null(), ptr::null_mut()) {
+				0 => Ok(Encoder(self)),
+				e => Err(Error::from(e))
+			}
+		}
+	}
 
-			match avcodec_encode_audio2(self.as_mut_ptr(), out.as_mut_ptr(), frame.as_ptr(), &mut got) {
-				e if e < 0 => Err(Error::from(e)),
-				_          => Ok(got != 0)
+	pub fn open_as(mut self, codec: &Codec) -> Result<Encoder, Error> {
+		unsafe {
+			if codec.is_encoder() {
+				match avcodec_open2(self.as_mut_ptr(), codec.as_ptr(), ptr::null_mut()) {
+					0 => Ok(Encoder(self)),
+					e => Err(Error::from(e))
+				}
+			}
+			else {
+				Err(Error::InvalidData)
+			}
+		}
+	}
+
+	pub fn open_as_with(mut self, codec: &Codec, options: Dictionary) -> Result<Encoder, Error> {
+		unsafe {
+			if codec.is_encoder() {
+				match avcodec_open2(self.as_mut_ptr(), codec.as_ptr(), &mut options.take()) {
+					0 => Ok(Encoder(self)),
+					e => Err(Error::from(e))
+				}
+			}
+			else {
+				Err(Error::InvalidData)
 			}
 		}
 	}
 }
 
 impl Deref for Audio {
-	type Target = Encoder;
+	type Target = Super;
 
 	fn deref(&self) -> &<Self as Deref>::Target {
 		&self.0
@@ -35,3 +62,26 @@ impl DerefMut for Audio {
 		&mut self.0
 	}
 }
+
+pub struct Encoder(pub Audio);
+
+impl Encoder {
+	pub fn encode(&mut self, frame: &frame::Audio, out: &mut Packet) -> Result<bool, Error> {
+		unsafe {
+			let mut got: c_int = 0;
+
+			match avcodec_encode_audio2(self.0.as_mut_ptr(), out.as_mut_ptr(), frame.as_ptr(), &mut got) {
+				e if e < 0 => Err(Error::from(e)),
+				_          => Ok(got != 0)
+			}
+		}
+	}
+}
+
+impl Deref for Encoder {
+	type Target = Audio;
+
+	fn deref(&self) -> &<Self as Deref>::Target {
+		&self.0
+	}
+}