codec/context: make destructors safe

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),
+			}
+		}
+	}
+}