Add Output::add_stream_with(&Context)

Calls `avcodec_parameters_from_context` to set the stream attributes from an AVCodecContext.

src/format/context/output.rs

@@ -9,7 +9,7 @@ use super::common::Context;
 use super::destructor;
 use codec::traits;
 use ffi::*;
-use {format, ChapterMut, Dictionary, Error, Rational, StreamMut};
+use {codec, format, ChapterMut, Dictionary, Error, Rational, StreamMut};
 
 pub struct Output {
     ptr: *mut AVFormatContext,
@@ -86,6 +86,25 @@ impl Output {
         }
     }
 
+    pub fn add_stream_with(&mut self, context: &codec::Context) -> Result<StreamMut, Error> {
+        unsafe {
+            let ptr = avformat_new_stream(self.as_mut_ptr(), ptr::null());
+
+            if ptr.is_null() {
+                return Err(Error::Unknown);
+            }
+
+            match avcodec_parameters_from_context((*ptr).codecpar, context.as_ptr()) {
+                0 => (),
+                e => return Err(Error::from(e)),
+            }
+
+            let index = (*self.ctx.as_ptr()).nb_streams - 1;
+
+            Ok(StreamMut::wrap(&mut self.ctx, index as usize))
+        }
+    }
+
     pub fn add_chapter<R: Into<Rational>, S: AsRef<str>>(
         &mut self,
         id: i64,