fix(codec): use a *const pointer

src/codec/codec.rs

@@ -5,22 +5,18 @@ use crate::{ffi::*, media, Error};
 
 #[derive(PartialEq, Eq, Copy, Clone)]
 pub struct Codec {
-	ptr: *mut AVCodec,
+	ptr: *const AVCodec,
 }
 
 unsafe impl Send for Codec {}
 unsafe impl Sync for Codec {}
 
 impl Codec {
-	pub unsafe fn wrap(ptr: *mut AVCodec) -> Self {
+	pub unsafe fn wrap(ptr: *const AVCodec) -> Self {
 		Codec { ptr }
 	}
 
 	pub unsafe fn as_ptr(&self) -> *const AVCodec {
-		self.ptr as *const _
-	}
-
-	pub unsafe fn as_mut_ptr(&mut self) -> *mut AVCodec {
 		self.ptr
 	}
 }

src/format/context/common.rs

@@ -172,13 +172,13 @@ impl<'a> Best<'a> {
 		'a: 'b,
 	{
 		unsafe {
-			let mut decoder = ptr::null_mut();
+			let mut decoder = ptr::null::<AVCodec>();
 			let index = av_find_best_stream(
 				self.context.ptr,
 				kind.into(),
 				self.wanted as c_int,
 				self.related as c_int,
-				&mut decoder,
+				&mut decoder as *mut _,
 				0,
 			);