diff --git a/src/codec/context.rs b/src/codec/context.rs
index 536abee..549e264 100644
--- a/src/codec/context.rs
+++ b/src/codec/context.rs
@@ -1,4 +1,5 @@
 use std::ptr;
+use std::rc::Rc;
 
 use libc::c_int;
 use ffi::*;
@@ -9,16 +10,15 @@ use super::decoder::Decoder;
 use super::encoder::Encoder;
 
 pub struct Context {
-	ptr: *mut AVCodecContext,
-
-	_own: bool,
+	ptr:   *mut AVCodecContext,
+	owner: Option<Rc<Drop>>,
 }
 
 unsafe impl Send for Context { }
 
 impl Context {
-	pub unsafe fn wrap(ptr: *mut AVCodecContext) -> Self {
-		Context { ptr: ptr, _own: false }
+	pub unsafe fn wrap(ptr: *mut AVCodecContext, owner: Option<Rc<Drop>>) -> Self {
+		Context { ptr: ptr, owner: owner }
 	}
 
 	pub unsafe fn as_ptr(&self) -> *const AVCodecContext {
@@ -33,7 +33,7 @@ impl Context {
 impl Context {
 	pub fn new() -> Self {
 		unsafe {
-			Context { ptr: avcodec_alloc_context3(ptr::null()), _own: true }
+			Context { ptr: avcodec_alloc_context3(ptr::null()), owner: None }
 		}
 	}
 
@@ -107,8 +107,8 @@ impl Context {
 
 impl Drop for Context {
 	fn drop(&mut self) {
-		if self._own {
-			unsafe {
+		unsafe {
+			if self.owner.is_none() {
 				avcodec_free_context(&mut self.as_mut_ptr());
 			}
 		}
diff --git a/src/codec/encoder/mod.rs b/src/codec/encoder/mod.rs
index 5dd7a72..8fd32c3 100644
--- a/src/codec/encoder/mod.rs
+++ b/src/codec/encoder/mod.rs
@@ -1,11 +1,11 @@
 pub mod video;
-pub use self::video::Video;
+pub use self::video::Encoder as Video;
 
 pub mod audio;
-pub use self::audio::Audio;
+pub use self::audio::Encoder as Audio;
 
 pub mod subtitle;
-pub use self::subtitle::Subtitle;
+pub use self::subtitle::Encoder as Subtitle;
 
 pub mod motion_estimation;
 pub use self::motion_estimation::MotionEstimation;
@@ -31,27 +31,27 @@ use ::media;
 pub struct Encoder(pub Context);
 
 impl Encoder {
-	pub fn video(self) -> Result<Video, Error> {
+	pub fn video(self) -> Result<video::Video, Error> {
 		if self.medium() == media::Type::Video {
-			Ok(Video(self))
+			Ok(video::Video(self))
 		}
 		else {
 			Err(Error::InvalidData)
 		}
 	}
 
-	pub fn audio(self) -> Result<Audio, Error> {
+	pub fn audio(self) -> Result<audio::Audio, Error> {
 		if self.medium() == media::Type::Audio {
-			Ok(Audio(self))
+			Ok(audio::Audio(self))
 		}
 		else {
 			Err(Error::InvalidData)
 		}
 	}
 
-	pub fn subtitle(self) -> Result<Subtitle, Error> {
+	pub fn subtitle(self) -> Result<subtitle::Subtitle, Error> {
 		if self.medium() == media::Type::Subtitle {
-			Ok(Subtitle(self))
+			Ok(subtitle::Subtitle(self))
 		}
 		else {
 			Err(Error::InvalidData)
diff --git a/src/codec/packet/side_data.rs b/src/codec/packet/side_data.rs
index 4a2e898..1366de7 100644
--- a/src/codec/packet/side_data.rs
+++ b/src/codec/packet/side_data.rs
@@ -87,10 +87,6 @@ impl<'a> SideData<'a> {
 	pub unsafe fn as_ptr(&self) -> *const AVPacketSideData {
 		self.ptr as *const _
 	}
-	
-	pub unsafe fn as_mut_ptr(&mut self) -> *mut AVPacketSideData {
-		self.ptr
-	}
 }
 
 impl<'a> SideData<'a> {
diff --git a/src/format/context/common.rs b/src/format/context/common.rs
index 4d8baea..a306e0c 100644
--- a/src/format/context/common.rs
+++ b/src/format/context/common.rs
@@ -1,19 +1,22 @@
-use std::marker::PhantomData;
+use std::rc::Rc;
 use std::ptr;
+use std::mem;
 
 use ffi::*;
 use libc::{c_int, c_uint};
 use ::{media, Stream, StreamMut, DictionaryRef};
+use super::destructor::{self, Destructor};
 
 pub struct Context {
-	ptr: *mut AVFormatContext,
+	ptr:  *mut AVFormatContext,
+	dtor: Rc<Destructor>,
 }
 
 unsafe impl Send for Context { }
 
 impl Context {
-	pub unsafe fn wrap(ptr: *mut AVFormatContext) -> Self {
-		Context { ptr: ptr }
+	pub unsafe fn wrap(ptr: *mut AVFormatContext, mode: destructor::Mode) -> Self {
+		Context { ptr: ptr, dtor: Rc::new(Destructor::new(ptr, mode)) }
 	}
 
 	pub unsafe fn as_ptr(&self) -> *const AVFormatContext {
@@ -23,6 +26,10 @@ impl Context {
 	pub unsafe fn as_mut_ptr(&mut self) -> *mut AVFormatContext {
 		self.ptr
 	}
+
+	pub unsafe fn destructor(&self) -> Rc<Destructor> {
+		self.dtor.clone()
+	}
 }
 
 impl Context {
@@ -32,7 +39,7 @@ impl Context {
 				None
 			}
 			else {
-				Some(Stream::wrap(*(*self.as_ptr()).streams.offset(index as isize)))
+				Some(Stream::wrap(self, index))
 			}
 		}
 	}
@@ -43,21 +50,17 @@ impl Context {
 				None
 			}
 			else {
-				Some(StreamMut::wrap(*(*self.as_mut_ptr()).streams.offset(index as isize)))
+				Some(StreamMut::wrap(self, index))
 			}
 		}
 	}
 
 	pub fn streams(&self) -> StreamIter {
-		unsafe {
-			StreamIter::new(self.as_ptr())
-		}
+		StreamIter::new(self)
 	}
 
 	pub fn streams_mut(&mut self) -> StreamIterMut {
-		unsafe {
-			StreamIterMut::new(self.as_mut_ptr())
-		}
+		StreamIterMut::new(self)
 	}
 
 	pub fn metadata(&self) -> DictionaryRef {
@@ -68,23 +71,19 @@ impl Context {
 }
 
 pub struct Best<'a> {
-	ptr: *const AVFormatContext,
+	context: &'a Context,
 
 	wanted:  i32,
 	related: i32,
-
-	_marker: PhantomData<&'a ()>,
 }
 
 impl<'a> Best<'a> {
-	pub unsafe fn new<'b>(ptr: *const AVFormatContext) -> Best<'b> {
+	pub unsafe fn new<'b, 'c: 'b>(context: &'c Context) -> Best<'b> {
 		Best {
-			ptr: ptr,
+			context: context,
 
 			wanted:  -1,
 			related: -1,
-
-			_marker: PhantomData,
 		}
 	}
 
@@ -101,12 +100,12 @@ impl<'a> Best<'a> {
 	pub fn best<'b>(self, kind: media::Type) -> Option<Stream<'b>> where 'a: 'b {
 		unsafe {
 			let mut decoder = ptr::null_mut();
-			let     index   = av_find_best_stream(self.ptr,
+			let     index   = av_find_best_stream(self.context.as_ptr(),
 				kind.into(), self.wanted as c_int, self.related as c_int,
 				&mut decoder, 0);
 
 			if index >= 0 && !decoder.is_null() {
-				Some(Stream::wrap(*(*self.ptr).streams.offset(index as isize)))
+				Some(Stream::wrap(self.context, index as usize))
 			}
 			else {
 				None
@@ -116,34 +115,32 @@ impl<'a> Best<'a> {
 }
 
 pub struct StreamIter<'a> {
-	ptr: *const AVFormatContext,
-	cur: c_uint,
-
-	_marker: PhantomData<&'a ()>,
+	context: &'a Context,
+	current: c_uint,
 }
 
 impl<'a> StreamIter<'a> {
-	pub fn new(ptr: *const AVFormatContext) -> Self {
-		StreamIter { ptr: ptr, cur: 0, _marker: PhantomData }
+	pub fn new<'s, 'c: 's>(context: &'c Context) -> StreamIter<'s> {
+		StreamIter { context: context, current: 0 }
 	}
 }
 
 impl<'a> StreamIter<'a> {
-	pub fn wanted<'b: 'a, 'c: 'a>(&'a self, stream: &'b Stream) -> Best<'a> {
+	pub fn wanted<'b, 'c>(&self, stream: &'b Stream) -> Best<'c> where 'a: 'b, 'a: 'c {
 		unsafe {
-			Best::new(self.ptr).wanted(stream)
+			Best::new(self.context).wanted(stream)
 		}
 	}
 
-	pub fn related<'b: 'a>(&'a self, stream: &'b Stream) -> Best<'a> {
+	pub fn related<'b, 'c>(&self, stream: &'b Stream) -> Best<'c> where 'a: 'b, 'a: 'c {
 		unsafe {
-			Best::new(self.ptr).related(stream)
+			Best::new(self.context).related(stream)
 		}
 	}
 
-	pub fn best<'b: 'a>(&'a self, kind: media::Type) -> Option<Stream<'b>> {
+	pub fn best<'b>(&self, kind: media::Type) -> Option<Stream<'b>> where 'a: 'b {
 		unsafe {
-			Best::new(self.ptr).best(kind)
+			Best::new(self.context).best(kind)
 		}
 	}
 }
@@ -153,19 +150,21 @@ impl<'a> Iterator for StreamIter<'a> {
 
 	fn next(&mut self) -> Option<<Self as Iterator>::Item> {
 		unsafe {
-			if self.cur >= (*self.ptr).nb_streams {
-				None
-			}
-			else {
-				self.cur += 1;
-				Some(Stream::wrap(*(*self.ptr).streams.offset((self.cur - 1) as isize)))
+			if self.current >= (*self.context.as_ptr()).nb_streams {
+				return None;
 			}
+
+			self.current += 1;
+
+			Some(Stream::wrap(self.context, (self.current - 1) as usize))
 		}
 	}
 
 	fn size_hint(&self) -> (usize, Option<usize>) {
 		unsafe {
-			((*self.ptr).nb_streams as usize, Some((*self.ptr).nb_streams as usize))
+			let length = (*self.context.as_ptr()).nb_streams as usize;
+
+			(length - self.current as usize, Some(length - self.current as usize))
 		}
 	}
 }
@@ -173,15 +172,13 @@ impl<'a> Iterator for StreamIter<'a> {
 impl<'a> ExactSizeIterator for StreamIter<'a> { }
 
 pub struct StreamIterMut<'a> {
-	ptr: *const AVFormatContext,
-	cur: c_uint,
-
-	_marker: PhantomData<&'a ()>,
+	context: &'a mut Context,
+	current: c_uint,
 }
 
 impl<'a> StreamIterMut<'a> {
-	pub fn new(ptr: *mut AVFormatContext) -> Self {
-		StreamIterMut { ptr: ptr, cur: 0, _marker: PhantomData }
+	pub fn new<'s, 'c: 's>(context: &'c mut Context) -> StreamIterMut<'s> {
+		StreamIterMut { context: context, current: 0 }
 	}
 }
 
@@ -190,19 +187,21 @@ impl<'a> Iterator for StreamIterMut<'a> {
 
 	fn next(&mut self) -> Option<<Self as Iterator>::Item> {
 		unsafe {
-			if self.cur >= (*self.ptr).nb_streams {
-				None
-			}
-			else {
-				self.cur += 1;
-				Some(StreamMut::wrap(*(*self.ptr).streams.offset((self.cur - 1) as isize)))
+			if self.current >= (*self.context.as_ptr()).nb_streams {
+				return None
 			}
+
+			self.current += 1;
+
+			Some(StreamMut::wrap(mem::transmute_copy(&self.context), (self.current - 1) as usize))
 		}
 	}
 
 	fn size_hint(&self) -> (usize, Option<usize>) {
 		unsafe {
-			((*self.ptr).nb_streams as usize, Some((*self.ptr).nb_streams as usize))
+			let length = (*self.context.as_ptr()).nb_streams as usize;
+
+			(length - self.current as usize, Some(length - self.current as usize))
 		}
 	}
 }
diff --git a/src/format/context/destructor.rs b/src/format/context/destructor.rs
new file mode 100644
index 0000000..7c90996
--- /dev/null
+++ b/src/format/context/destructor.rs
@@ -0,0 +1,35 @@
+use ffi::*;
+
+#[derive(Copy, Clone, Debug)]
+pub enum Mode {
+	Input,
+	Output,
+}
+
+pub struct Destructor {
+	ptr:  *mut AVFormatContext,
+	mode: Mode,
+}
+
+impl Destructor {
+	pub unsafe fn new(ptr: *mut AVFormatContext, mode: Mode) -> Self {
+		Destructor {
+			ptr:  ptr,
+			mode: mode,
+		}
+	}
+}
+
+impl Drop for Destructor {
+	fn drop(&mut self) {
+		unsafe {
+			match self.mode {
+				Mode::Input =>
+					avformat_close_input(&mut self.ptr),
+
+				Mode::Output =>
+					avformat_free_context(self.ptr),
+			}
+		}
+	}
+}
diff --git a/src/format/context/input.rs b/src/format/context/input.rs
index f87a69e..fba7c19 100644
--- a/src/format/context/input.rs
+++ b/src/format/context/input.rs
@@ -1,10 +1,12 @@
 use std::ops::{Deref, DerefMut};
 use std::ptr;
+use std::mem;
 use std::ffi::CString;
 
 use ffi::*;
 use ::{Error, Codec, Stream, Packet, format};
 use super::common::Context;
+use super::destructor;
 
 pub struct Input {
 	ptr: *mut AVFormatContext,
@@ -15,7 +17,7 @@ unsafe impl Send for Input { }
 
 impl Input {
 	pub unsafe fn wrap(ptr: *mut AVFormatContext) -> Self {
-		Input { ptr: ptr, ctx: Context::wrap(ptr) }
+		Input { ptr: ptr, ctx: Context::wrap(ptr, destructor::Mode::Input) }
 	}
 
 	pub unsafe fn as_ptr(&self) -> *const AVFormatContext {
@@ -135,14 +137,6 @@ impl DerefMut for Input {
 	}
 }
 
-impl Drop for Input {
-	fn drop(&mut self) {
-		unsafe {
-			avformat_close_input(&mut self.as_mut_ptr());
-		}
-	}
-}
-
 pub struct PacketIter<'a> {
 	context: &'a mut Input,
 }
@@ -161,10 +155,11 @@ impl<'a> Iterator for PacketIter<'a> {
 
 		loop {
 			match packet.read(self.context) {
-				Ok(..) =>
-					return Some((unsafe {
-						Stream::wrap(*(*self.context.as_ptr()).streams.offset(packet.stream() as isize))
-					}, packet)),
+				Ok(..) => unsafe {
+					return Some((
+						Stream::wrap(mem::transmute_copy(&self.context), packet.stream()),
+						packet));
+				},
 
 				Err(Error::Eof) =>
 					return None,
diff --git a/src/format/context/mod.rs b/src/format/context/mod.rs
index 8ae0257..512b1b0 100644
--- a/src/format/context/mod.rs
+++ b/src/format/context/mod.rs
@@ -1,3 +1,6 @@
+pub mod destructor;
+pub use self::destructor::Destructor;
+
 pub mod input;
 pub use self::input::Input;
 
diff --git a/src/format/context/output.rs b/src/format/context/output.rs
index b1f90ec..3a6ceed 100644
--- a/src/format/context/output.rs
+++ b/src/format/context/output.rs
@@ -5,6 +5,7 @@ use std::ffi::CString;
 use ffi::*;
 use ::{Error, Codec, StreamMut, Dictionary, format};
 use super::common::Context;
+use super::destructor;
 
 pub struct Output {
 	ptr: *mut AVFormatContext,
@@ -15,7 +16,7 @@ unsafe impl Send for Output { }
 
 impl Output {
 	pub unsafe fn wrap(ptr: *mut AVFormatContext) -> Self {
-		Output { ptr: ptr, ctx: Context::wrap(ptr) }
+		Output { ptr: ptr, ctx: Context::wrap(ptr, destructor::Mode::Output) }
 	}
 
 	pub unsafe fn as_ptr(&self) -> *const AVFormatContext {
@@ -74,7 +75,9 @@ impl Output {
 				panic!("out of memory");
 			}
 
-			StreamMut::wrap(ptr)
+			let index = (*self.ctx.as_ptr()).nb_streams - 1;
+
+			StreamMut::wrap(&mut self.ctx, index as usize)
 		}
 	}
 
@@ -99,14 +102,6 @@ impl DerefMut for Output {
 	}
 }
 
-impl Drop for Output {
-	fn drop(&mut self) {
-		unsafe {
-			avformat_free_context(self.as_mut_ptr());
-		}
-	}
-}
-
 pub fn dump(ctx: &Output, index: i32, url: Option<&str>) {
 	let url = url.map(|u| CString::new(u).unwrap());
 
diff --git a/src/format/stream/stream.rs b/src/format/stream/stream.rs
index 7204ed1..596edb9 100644
--- a/src/format/stream/stream.rs
+++ b/src/format/stream/stream.rs
@@ -1,33 +1,29 @@
-use std::marker::PhantomData;
-
 use libc::c_int;
 use ffi::*;
-use ::format;
 use ::codec::{self, packet};
 use ::{Rational, Discard};
 use super::Disposition;
+use format::context::common::Context;
 
-#[derive(Eq, PartialEq)]
 pub struct Stream<'a> {
-	ptr: *mut AVStream,
-
-	_marker: PhantomData<&'a format::Context>,
+	context: &'a Context,
+	index:   usize,
 }
 
 impl<'a> Stream<'a> {
-	pub unsafe fn wrap(ptr: *mut AVStream) -> Self {
-		Stream { ptr: ptr, _marker: PhantomData }
+	pub unsafe fn wrap(context: &Context, index: usize) -> Stream {
+		Stream { context: context, index: index }
 	}
 
 	pub unsafe fn as_ptr(&self) -> *const AVStream {
-		self.ptr as *const _
+		*(*self.context.as_ptr()).streams.offset(self.index as isize)
 	}
 }
 
 impl<'a> Stream<'a> {
 	pub fn codec(&self) -> codec::Context {
 		unsafe {
-			codec::Context::wrap((*self.as_ptr()).codec)
+			codec::Context::wrap((*self.as_ptr()).codec, Some(self.context.destructor()))
 		}
 	}
 
@@ -74,9 +70,7 @@ impl<'a> Stream<'a> {
 	}
 
 	pub fn side_data(&self) -> SideDataIter {
-		unsafe {
-			SideDataIter::new(self.as_ptr())
-		}
+		SideDataIter::new(self)
 	}
 
 	pub fn frame_rate(&self) -> Rational {
@@ -86,16 +80,24 @@ impl<'a> Stream<'a> {
 	}
 }
 
-pub struct SideDataIter<'a> {
-	ptr: *const AVStream,
-	cur: c_int,
+impl<'a> PartialEq for Stream<'a> {
+	fn eq(&self, other: &Self) -> bool {
+		unsafe {
+			self.as_ptr() == other.as_ptr()
+		}
+	}
+}
 
-	_marker: PhantomData<&'a Stream<'a>>,
+impl<'a> Eq for Stream<'a> { }
+
+pub struct SideDataIter<'a> {
+	stream: &'a Stream<'a>,
+	current: c_int,
 }
 
 impl<'a> SideDataIter<'a> {
-	pub fn new(ptr: *const AVStream) -> Self {
-		SideDataIter { ptr: ptr, cur: 0, _marker: PhantomData }
+	pub fn new<'sd, 's: 'sd>(stream: &'s Stream) -> SideDataIter<'sd> {
+		SideDataIter { stream: stream, current: 0 }
 	}
 }
 
@@ -104,19 +106,22 @@ impl<'a> Iterator for SideDataIter<'a> {
 
 	fn next(&mut self) -> Option<<Self as Iterator>::Item> {
 		unsafe {
-			if self.cur >= (*self.ptr).nb_side_data {
-				None
-			}
-			else {
-				self.cur += 1;
-				Some(packet::SideData::wrap((*self.ptr).side_data.offset((self.cur - 1) as isize)))
+			if self.current >= (*self.stream.as_ptr()).nb_side_data {
+				return None;
 			}
+
+			self.current += 1;
+
+			Some(packet::SideData::wrap(
+				(*self.stream.as_ptr()).side_data.offset((self.current - 1) as isize)))
 		}
 	}
 
 	fn size_hint(&self) -> (usize, Option<usize>) {
 		unsafe {
-			((*self.ptr).nb_side_data as usize, Some((*self.ptr).nb_side_data as usize))
+			let length = (*self.stream.as_ptr()).nb_side_data as usize;
+
+			(length - self.current as usize, Some(length - self.current as usize))
 		}
 	}
 }
diff --git a/src/format/stream/stream_mut.rs b/src/format/stream/stream_mut.rs
index 65e773c..4c98c19 100644
--- a/src/format/stream/stream_mut.rs
+++ b/src/format/stream/stream_mut.rs
@@ -1,26 +1,30 @@
 use std::ops::Deref;
+use std::mem;
 
 use ffi::*;
 use ::Rational;
 use super::Stream;
+use format::context::common::Context;
 
-#[derive(Eq, PartialEq)]
 pub struct StreamMut<'a> {
-	ptr: *mut AVStream,
-	imm: Stream<'a>,
+	context: &'a mut Context,
+	index:   usize,
+
+	immutable: Stream<'a>,
 }
 
 impl<'a> StreamMut<'a> {
-	pub unsafe fn wrap(ptr: *mut AVStream) -> Self {
-		StreamMut { ptr: ptr, imm: Stream::wrap(ptr) }
-	}
+	pub unsafe fn wrap(context: &mut Context, index: usize) -> StreamMut {
+		StreamMut {
+			context: mem::transmute_copy(&context),
+			index:   index,
 
-	pub unsafe fn as_ptr(&self) -> *const AVStream {
-		self.ptr as *const _
+			immutable: Stream::wrap(mem::transmute_copy(&context), index)
+		}
 	}
 
 	pub unsafe fn as_mut_ptr(&mut self) -> *mut AVStream {
-		self.ptr
+		*(*self.context.as_mut_ptr()).streams.offset(self.index as isize)
 	}
 }
 
@@ -42,6 +46,6 @@ impl<'a> Deref for StreamMut<'a> {
 	type Target = Stream<'a>;
 
 	fn deref(&self) -> &Self::Target {
-		&self.imm
+		&self.immutable
 	}
 }