codec: expose modern send/receive packet/frame APIs

avcodec_encode_video2()/avcodec_decode_video2/avcodec_encode_audio2()/avcodec_decode_audio4()
have been deprecated since FFmpeg 3.1, with modern
avcodec_send_packet()/avcodec_receive_frame()/avcodec_send_frame()/avcodec_receive_packet()
as replacements.

This commit adds send_packet(), send_eof() and receive_frame() to
decoder::Opened; send_frame(), send_eof() and receive_packet() to
encoder::Encoder to expose these modern APIs.

src/codec/decoder/opened.rs

@@ -1,10 +1,10 @@
 use std::ops::{Deref, DerefMut};
+use std::ptr;
 
 use super::{Audio, Decoder, Subtitle, Video};
 use codec::{Context, Profile};
 use ffi::*;
-use media;
+use {media, packet, Error, Frame, Rational};
-use {Error, Rational};
 
 pub struct Opened(pub Decoder);
 
@@ -33,6 +33,35 @@ impl Opened {
         }
     }
 
+    pub fn send_packet<P: packet::Ref>(&mut self, packet: &P) -> Result<(), Error> {
+        unsafe {
+            match avcodec_send_packet(self.as_mut_ptr(), packet.as_ptr()) {
+                e if e < 0 => Err(Error::from(e)),
+                _ => Ok(()),
+            }
+        }
+    }
+
+    /// Sends a NULL packet to the decoder to signal end of stream and enter
+    /// draining mode.
+    pub fn send_eof(&mut self) -> Result<(), Error> {
+        unsafe {
+            match avcodec_send_packet(self.as_mut_ptr(), ptr::null()) {
+                e if e < 0 => Err(Error::from(e)),
+                _ => Ok(()),
+            }
+        }
+    }
+
+    pub fn receive_frame(&mut self, frame: &mut Frame) -> Result<(), Error> {
+        unsafe {
+            match avcodec_receive_frame(self.as_mut_ptr(), frame.as_mut_ptr()) {
+                e if e < 0 => Err(Error::from(e)),
+                _ => Ok(()),
+            }
+        }
+    }
+
     pub fn bit_rate(&self) -> usize {
         unsafe { (*self.as_ptr()).bit_rate as usize }
     }

src/codec/encoder/encoder.rs

@@ -1,9 +1,12 @@
 use std::ops::{Deref, DerefMut};
+use std::ptr;
+
+use ffi::*;
+use libc::c_int;
 
 use super::{audio, subtitle, video};
 use codec::Context;
-use libc::c_int;
+use {media, packet, Error, Frame, Rational};
-use {media, Error, Rational};
 
 pub struct Encoder(pub Context);
 
@@ -56,6 +59,30 @@ impl Encoder {
         }
     }
 
+    pub fn send_frame(&mut self, frame: &Frame) -> Result<(), Error> {
+        unsafe {
+            match avcodec_send_frame(self.as_mut_ptr(), frame.as_ptr()) {
+                e if e < 0 => Err(Error::from(e)),
+                _ => Ok(()),
+            }
+        }
+    }
+
+    /// Sends a NULL packet to the encoder to signal end of stream and enter
+    /// draining mode.
+    pub fn send_eof(&mut self) -> Result<(), Error> {
+        unsafe { self.send_frame(&Frame::wrap(ptr::null_mut())) }
+    }
+
+    pub fn receive_packet<P: packet::Mut>(&mut self, packet: &mut P) -> Result<(), Error> {
+        unsafe {
+            match avcodec_receive_packet(self.as_mut_ptr(), packet.as_mut_ptr()) {
+                e if e < 0 => Err(Error::from(e)),
+                _ => Ok(()),
+            }
+        }
+    }
+
     pub fn set_bit_rate(&mut self, value: usize) {
         unsafe {
             (*self.as_mut_ptr()).bit_rate = value as i64;