media: ffmpeg: add proper wrapper for AVProfile

Our ffmpeg crate should avoid returning native C avcodec types if
possible, as this means client code could have to resort to unsafe code.
Fix this for AVProfile by introducing a safe wrapper type that provides
us all the useful methods we may need.

BUG=b:169295147
TEST=cargo build --features "video-decoder,ffmpeg"

Change-Id: I2436857d3878b5b6cf4eab35f5b3b0c57c8db60e
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3782039
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
Tested-by: Alexandre Courbot <acourbot@chromium.org>
Auto-Submit: Alexandre Courbot <acourbot@chromium.org>

devices/src/virtio/video/decoder/backend/ffmpeg.rs

@@ -633,7 +633,7 @@ impl DecoderBackend for FfmpegDecoder {
 
                     profile_iter
                         .filter_map(|p| {
-                            match p.profile as u32 {
+                            match p.profile() {
                                 FF_PROFILE_H264_BASELINE => Some(Profile::H264Baseline),
                                 FF_PROFILE_H264_MAIN => Some(Profile::H264Main),
                                 FF_PROFILE_H264_EXTENDED => Some(Profile::H264Extended),
@@ -662,7 +662,7 @@ impl DecoderBackend for FfmpegDecoder {
                     ]
                 }
                 Format::VP9 => profile_iter
-                    .filter_map(|p| match p.profile as u32 {
+                    .filter_map(|p| match p.profile() {
                         FF_PROFILE_VP9_0 => Some(Profile::VP9Profile0),
                         FF_PROFILE_VP9_1 => Some(Profile::VP9Profile1),
                         FF_PROFILE_VP9_2 => Some(Profile::VP9Profile2),
@@ -671,7 +671,7 @@ impl DecoderBackend for FfmpegDecoder {
                     })
                     .collect(),
                 Format::Hevc => profile_iter
-                    .filter_map(|p| match p.profile as u32 {
+                    .filter_map(|p| match p.profile() {
                         FF_PROFILE_HEVC_MAIN => Some(Profile::HevcMain),
                         FF_PROFILE_HEVC_MAIN_10 => Some(Profile::HevcMain10),
                         FF_PROFILE_HEVC_MAIN_STILL_PICTURE => Some(Profile::HevcMainStillPicture),

media/ffmpeg/src/avcodec.rs

@@ -7,6 +7,7 @@
 //! low-level access as the libavcodec functions do.
 
 use std::ffi::CStr;
+use std::fmt::Debug;
 use std::fmt::Display;
 use std::marker::PhantomData;
 use std::ops::Deref;
@@ -139,11 +140,41 @@ impl Iterator for AvCodecIterator {
     }
 }
 
+/// Simple wrapper over `AVProfile` that provides helpful methods.
+pub struct AvProfile(&'static ffi::AVProfile);
+
+impl AvProfile {
+    /// Return the profile id, which can be matched against FF_PROFILE_*.
+    pub fn profile(&self) -> u32 {
+        self.0.profile as u32
+    }
+
+    /// Return the name of this profile.
+    pub fn name(&self) -> &'static str {
+        const INVALID_PROFILE_STR: &str = "invalid profile";
+
+        // Safe because `CStr::from_ptr` is called on a valid zero-terminated C string.
+        unsafe { CStr::from_ptr(self.0.name).to_str() }.unwrap_or(INVALID_PROFILE_STR)
+    }
+}
+
+impl Display for AvProfile {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(self.name())
+    }
+}
+
+impl Debug for AvProfile {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        Display::fmt(self, f)
+    }
+}
+
 /// Lightweight abstraction over the array of supported profiles for a given codec.
 pub struct AvProfileIterator(*const ffi::AVProfile);
 
 impl Iterator for AvProfileIterator {
-    type Item = &'static ffi::AVProfile;
+    type Item = AvProfile;
 
     fn next(&mut self) -> Option<Self::Item> {
         // Safe because the contract of `new` stipulates we have received a valid `AVCodec`
@@ -158,7 +189,7 @@ impl Iterator for AvProfileIterator {
                         // Safe because we have been initialized to a static, valid profiles array
                         // which is terminated by FF_PROFILE_UNKNOWN.
                         self.0 = unsafe { self.0.offset(1) };
-                        Some(profile)
+                        Some(AvProfile(profile))
                     }
                 }
             }