Add feature to disable decoder prioritization

By default, `media::DecoderSelector` uses a decoder prioritization
function that tries to balance power and performance with a resolution
-based hardware decoder cutoff. This CL adds a default-disabled feature
to instead use a function that prioritizes nothing, which is useful
for testing.

Bug: 684792
Change-Id: Iac0dc0e12fd9f5a41f344eefcbe002b4a1e84724
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2278702
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785868}

media/base/media_switches.cc

@@ -489,6 +489,11 @@ const base::Feature kHardwareMediaKeyHandling {
 #endif
 };
 
+// Enables a platform-specific resolution cutoff for prioritizing platform
+// decoders over software decoders or vice-versa.
+const base::Feature kResolutionBasedDecoderPriority{
+    "ResolutionBasedDecoderPriority", base::FEATURE_ENABLED_BY_DEFAULT};
+
 // Enables low-delay video rendering in media pipeline on "live" stream.
 const base::Feature kLowDelayVideoRenderingOnLiveStream{
     "low-delay-video-rendering-on-live-stream",

media/base/media_switches.h

@@ -173,6 +173,7 @@ MEDIA_EXPORT extern const base::Feature kVideoBlitColorAccuracy;
 MEDIA_EXPORT extern const base::Feature kWakeLockOptimisationHiddenMuted;
 MEDIA_EXPORT extern const base::Feature kWidevineAv1;
 MEDIA_EXPORT extern const base::Feature kWidevineAv1ForceSupportForTesting;
+MEDIA_EXPORT extern const base::Feature kResolutionBasedDecoderPriority;
 
 #if defined(ARCH_CPU_X86_FAMILY) && defined(OS_CHROMEOS)
 MEDIA_EXPORT extern const base::Feature kVp9kSVCHWDecoding;

media/filters/decoder_selector.cc

@@ -9,6 +9,7 @@
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
+#include "base/feature_list.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_functions.h"
@@ -20,6 +21,7 @@
 #include "media/base/cdm_context.h"
 #include "media/base/demuxer_stream.h"
 #include "media/base/media_log.h"
+#include "media/base/media_switches.h"
 #include "media/base/video_decoder.h"
 #include "media/filters/decoder_stream_traits.h"
 #include "media/filters/decrypting_demuxer_stream.h"
@@ -30,6 +32,11 @@ namespace {
 
 const char kSelectDecoderTrace[] = "DecoderSelector::SelectDecoder";
 
+template <typename T>
+DecoderPriority UnspecifiedDecoderPriority(const T& /*config*/) {
+  return DecoderPriority::kUnspecified;
+}
+
 DecoderPriority GetDefaultVideoDecoderPriority(
     const VideoDecoderConfig& config) {
 #if defined(OS_ANDROID)
@@ -44,18 +51,19 @@ DecoderPriority GetDefaultVideoDecoderPriority(
              : DecoderPriority::kPreferPlatformDecoders;
 }
 
-DecoderPriority GetDefaultAudioDecoderPriority(
-    const AudioDecoderConfig& /*config*/) {
-  // Platform audio decoders are not currently prioritized or deprioritized
-  return DecoderPriority::kUnspecified;
-}
-
 void SetDefaultDecoderPriorityCB(VideoDecoderSelector::DecoderPriorityCB* out) {
+  if (base::FeatureList::IsEnabled(kResolutionBasedDecoderPriority)) {
     *out = base::BindRepeating(GetDefaultVideoDecoderPriority);
+  } else {
+    *out = base::BindRepeating<DecoderPriority(const VideoDecoderConfig&)>(
+        UnspecifiedDecoderPriority);
+  }
 }
 
 void SetDefaultDecoderPriorityCB(AudioDecoderSelector::DecoderPriorityCB* out) {
-  *out = base::BindRepeating(GetDefaultAudioDecoderPriority);
+  // Platform audio decoders are not currently prioritized or deprioritized
+  *out = base::BindRepeating<DecoderPriority(const AudioDecoderConfig&)>(
+      UnspecifiedDecoderPriority);
 }
 
 }  // namespace