diff --git a/src/codec/packet/packet.rs b/src/codec/packet/packet.rs
index 4d43bc1..427c1d6 100644
--- a/src/codec/packet/packet.rs
+++ b/src/codec/packet/packet.rs
@@ -127,9 +127,7 @@ impl Packet {
 
     #[inline]
     pub fn set_pts(&mut self, value: Option<i64>) {
-        unsafe {
-            (*self.as_mut_ptr()).pts = value.unwrap_or(AV_NOPTS_VALUE);
-        }
+        self.0.pts = value.unwrap_or(AV_NOPTS_VALUE);
     }
 
     #[inline]
@@ -142,9 +140,7 @@ impl Packet {
 
     #[inline]
     pub fn set_dts(&mut self, value: Option<i64>) {
-        unsafe {
-            (*self.as_mut_ptr()).dts = value.unwrap_or(AV_NOPTS_VALUE);
-        }
+        self.0.dts = value.unwrap_or(AV_NOPTS_VALUE);
     }
 
     #[inline]
@@ -157,11 +153,21 @@ impl Packet {
         self.0.duration as i64
     }
 
+    #[inline]
+    pub fn set_duration(&mut self, value: i64) {
+        self.0.duration = value;
+    }
+
     #[inline]
     pub fn position(&self) -> isize {
         self.0.pos as isize
     }
 
+    #[inline]
+    pub fn set_position(&mut self, value: isize) {
+        self.0.pos = value as i64
+    }
+
     #[inline]
     pub fn convergence(&self) -> isize {
         self.0.convergence_duration as isize
diff --git a/src/format/context/common.rs b/src/format/context/common.rs
index e441681..e937d8a 100644
--- a/src/format/context/common.rs
+++ b/src/format/context/common.rs
@@ -1,3 +1,4 @@
+use std::fmt;
 use std::mem;
 use std::ptr;
 use std::rc::Rc;
@@ -36,12 +37,17 @@ impl Context {
 }
 
 impl Context {
+    #[inline]
+    fn nb_streams(&self) -> u32 {
+        unsafe { (*self.as_ptr()).nb_streams }
+    }
+
     pub fn stream<'a, 'b>(&'a self, index: usize) -> Option<Stream<'b>>
     where
         'a: 'b,
     {
         unsafe {
-            if index >= (*self.as_ptr()).nb_streams as usize {
+            if index >= self.nb_streams() as usize {
                 None
             } else {
                 Some(Stream::wrap(self, index))
@@ -54,7 +60,7 @@ impl Context {
         'a: 'b,
     {
         unsafe {
-            if index >= (*self.as_ptr()).nb_streams as usize {
+            if index >= self.nb_streams() as usize {
                 None
             } else {
                 Some(StreamMut::wrap(self, index))
@@ -78,6 +84,7 @@ impl Context {
         unsafe { (*self.as_ptr()).duration }
     }
 
+    #[inline]
     pub fn nb_chapters(&self) -> u32 {
         unsafe { (*self.as_ptr()).nb_chapters }
     }
@@ -87,7 +94,7 @@ impl Context {
         'a: 'b,
     {
         unsafe {
-            if index >= (*self.as_ptr()).nb_chapters as usize {
+            if index >= self.nb_chapters() as usize {
                 None
             } else {
                 Some(Chapter::wrap(self, index))
@@ -100,7 +107,7 @@ impl Context {
         'a: 'b,
     {
         unsafe {
-            if index >= (*self.as_ptr()).nb_chapters as usize {
+            if index >= self.nb_chapters() as usize {
                 None
             } else {
                 Some(ChapterMut::wrap(self, index))
@@ -222,7 +229,7 @@ impl<'a> Iterator for StreamIter<'a> {
 
     fn next(&mut self) -> Option<<Self as Iterator>::Item> {
         unsafe {
-            if self.current >= (*self.context.as_ptr()).nb_streams {
+            if self.current >= self.context.nb_streams() {
                 return None;
             }
 
@@ -233,14 +240,12 @@ impl<'a> Iterator for StreamIter<'a> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        unsafe {
-            let length = (*self.context.as_ptr()).nb_streams as usize;
+        let length = self.context.nb_streams() as usize;
 
-            (
-                length - self.current as usize,
-                Some(length - self.current as usize),
-            )
-        }
+        (
+            length - self.current as usize,
+            Some(length - self.current as usize),
+        )
     }
 }
 
@@ -264,13 +269,12 @@ impl<'a> Iterator for StreamIterMut<'a> {
     type Item = StreamMut<'a>;
 
     fn next(&mut self) -> Option<<Self as Iterator>::Item> {
+        if self.current >= self.context.nb_streams() {
+            return None;
+        }
+        self.current += 1;
+
         unsafe {
-            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,
@@ -279,14 +283,12 @@ impl<'a> Iterator for StreamIterMut<'a> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        unsafe {
-            let length = (*self.context.as_ptr()).nb_streams as usize;
+        let length = self.context.nb_streams() as usize;
 
-            (
-                length - self.current as usize,
-                Some(length - self.current as usize),
-            )
-        }
+        (
+            length - self.current as usize,
+            Some(length - self.current as usize),
+        )
     }
 }
 
@@ -380,3 +382,14 @@ impl<'a> Iterator for ChapterIterMut<'a> {
 }
 
 impl<'a> ExactSizeIterator for ChapterIterMut<'a> {}
+
+impl fmt::Debug for Context {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        let mut s = fmt.debug_struct("AVFormatContext");
+        s.field("bit_rate", &self.bit_rate());
+        s.field("duration", &self.duration());
+        s.field("nb_chapters", &self.nb_chapters());
+        s.field("nb_streams", &self.nb_streams());
+        s.finish()
+    }
+}
diff --git a/src/format/context/output.rs b/src/format/context/output.rs
index 986715d..ceb1ec9 100644
--- a/src/format/context/output.rs
+++ b/src/format/context/output.rs
@@ -72,11 +72,12 @@ impl Output {
 
     pub fn add_stream<E: traits::Encoder>(&mut self, codec: E) -> Result<StreamMut, Error> {
         unsafe {
-            let codec = codec.encoder().ok_or(Error::EncoderNotFound)?;
-            let ptr = avformat_new_stream(self.as_mut_ptr(), codec.as_ptr());
+            let codec = codec.encoder();
+            let codec = codec.map_or(ptr::null(), |c| c.as_ptr());
+            let ptr = avformat_new_stream(self.as_mut_ptr(), codec);
 
             if ptr.is_null() {
-                panic!("out of memory");
+                return Err(Error::Unknown);
             }
 
             let index = (*self.ctx.as_ptr()).nb_streams - 1;
diff --git a/src/format/stream/stream.rs b/src/format/stream/stream.rs
index f7c2e0e..c951bab 100644
--- a/src/format/stream/stream.rs
+++ b/src/format/stream/stream.rs
@@ -5,6 +5,7 @@ use format::context::common::Context;
 use libc::c_int;
 use {DictionaryRef, Discard, Rational};
 
+#[derive(Debug)]
 pub struct Stream<'a> {
     context: &'a Context,
     index: usize,
diff --git a/src/software/resampling/context.rs b/src/software/resampling/context.rs
index fc3902c..9b390db 100644
--- a/src/software/resampling/context.rs
+++ b/src/software/resampling/context.rs
@@ -20,6 +20,8 @@ pub struct Context {
     output: Definition,
 }
 
+unsafe impl Send for Context {}
+
 impl Context {
     #[doc(hidden)]
     pub unsafe fn as_ptr(&self) -> *const SwrContext {
diff --git a/src/util/dictionary/immutable.rs b/src/util/dictionary/immutable.rs
index 3781277..677faf1 100644
--- a/src/util/dictionary/immutable.rs
+++ b/src/util/dictionary/immutable.rs
@@ -1,4 +1,5 @@
 use std::ffi::{CStr, CString};
+use std::fmt;
 use std::marker::PhantomData;
 use std::ptr;
 use std::str::from_utf8_unchecked;
@@ -58,3 +59,9 @@ impl<'a> IntoIterator for &'a Ref<'a> {
         self.iter()
     }
 }
+
+impl<'a> fmt::Debug for Ref<'a> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.debug_map().entries(self.iter()).finish()
+    }
+}
diff --git a/src/util/dictionary/mutable.rs b/src/util/dictionary/mutable.rs
index 5413dfd..241a39d 100644
--- a/src/util/dictionary/mutable.rs
+++ b/src/util/dictionary/mutable.rs
@@ -1,4 +1,5 @@
 use std::ffi::CString;
+use std::fmt;
 use std::marker::PhantomData;
 use std::ops::Deref;
 
@@ -50,3 +51,9 @@ impl<'a> Deref for Ref<'a> {
         &self.imm
     }
 }
+
+impl<'a> fmt::Debug for Ref<'a> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        self.imm.fmt(fmt)
+    }
+}
diff --git a/src/util/dictionary/owned.rs b/src/util/dictionary/owned.rs
index 00d06ed..16f2ba0 100644
--- a/src/util/dictionary/owned.rs
+++ b/src/util/dictionary/owned.rs
@@ -1,3 +1,4 @@
+use std::fmt;
 use std::iter::FromIterator;
 use std::ops::{Deref, DerefMut};
 use std::ptr;
@@ -126,3 +127,9 @@ impl<'a> Drop for Owned<'a> {
         }
     }
 }
+
+impl<'a> fmt::Debug for Owned<'a> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(fmt)
+    }
+}