Fix use of Android 11 low latency decoding feature

app/src/main/java/com/limelight/binding/video/MediaCodecHelper.java

@@ -706,6 +706,15 @@ public class MediaCodecHelper {
     // and we want to be sure all callers are handling this possibility
     @SuppressWarnings("RedundantThrows")
     private static MediaCodecInfo findKnownSafeDecoder(String mimeType, int requiredProfile) throws Exception {
+        // Some devices (Exynos devces, at least) have two sets of decoders.
+        // The first set of decoders are C2 which do not support FEATURE_LowLatency,
+        // but the second set of OMX decoders do support FEATURE_LowLatency. We want
+        // to pick the OMX decoders despite the fact that C2 is listed first.
+        // On some Qualcomm devices (like Pixel 4), there are separate low latency decoders
+        // (like c2.qti.hevc.decoder.low_latency) that advertise FEATURE_LowLatency while
+        // the standard ones (like c2.qti.hevc.decoder) do not. Like Exynos, the decoders
+        // with FEATURE_LowLatency support are listed after the standard ones.
+        for (int i = 0; i < 2; i++) {
             for (MediaCodecInfo codecInfo : getMediaCodecList()) {
                 // Skip encoders
                 if (codecInfo.isEncoder()) {
@@ -722,7 +731,7 @@ public class MediaCodecHelper {
                 // Find a decoder that supports the requested video format
                 for (String mime : codecInfo.getSupportedTypes()) {
                     if (mime.equalsIgnoreCase(mimeType)) {
-                    LimeLog.info("Examining decoder capabilities of "+codecInfo.getName());
+                        LimeLog.info("Examining decoder capabilities of " + codecInfo.getName() + " (round " + (i + 1) + ")");
 
                         // Skip blacklisted codecs
                         if (isCodecBlacklisted(codecInfo)) {
@@ -731,6 +740,11 @@ public class MediaCodecHelper {
 
                         CodecCapabilities caps = codecInfo.getCapabilitiesForType(mime);
 
+                        if (i == 0 && !decoderSupportsAndroidRLowLatency(codecInfo, mime)) {
+                            LimeLog.info("Skipping decoder that lacks FEATURE_LowLatency for round 1");
+                            continue;
+                        }
+
                         if (requiredProfile != -1) {
                             for (CodecProfileLevel profile : caps.profileLevels) {
                                 if (profile.profile == requiredProfile) {
@@ -740,13 +754,13 @@ public class MediaCodecHelper {
                             }
 
                             LimeLog.info("Decoder " + codecInfo.getName() + " does NOT support required profile");
-                    }
+                        } else {
-                    else {
                             return codecInfo;
                         }
                     }
                 }
             }
+        }
         
         return null;
     }

decoder-errata.txt

@@ -41,3 +41,6 @@ This file serves to document some of the decoder errata when using MediaCodec ha
 
 14. Some HEVC decoders lag when receiving a stream with 16 reference frames
 	- Affected decoders: Tegra X1 in Pixel C (but NOT in SHIELD TV darcy)
+
+15. Some devices that support Android 11's FEATURE_LowLatency don't support it on their first compatible H.264/HEVC decoder. It is important to examine *all* decoders for FEATURE_LowLatency before deciding on one.
+    - Affected devices: Pixel 4 (c2.qti.avc.decoder.low_latency vs c2.qti.avc.decoder) and Galaxy S21 Exynos (OMX.Exynos.avc.dec [FEATURE_LowLatency] vs C2.Exynos.avc.decoder [no FEATURE_LowLatency])