diff --git a/content/test/data/gpu/webcodecs/encode-decode.html b/content/test/data/gpu/webcodecs/encode-decode.html
index 8ed6fb3400ff22..3939c62efa59eb 100644
--- a/content/test/data/gpu/webcodecs/encode-decode.html
+++ b/content/test/data/gpu/webcodecs/encode-decode.html
@@ -10,7 +10,12 @@
   <script src="webcodecs_common.js"></script>
   <script type="text/javascript">
     'use strict';
-    const acceleration = 'prefer-hardware';
+    function showFrameForDebug(frame) {
+      const cnv = document.getElementById('debug_cnv');
+      var ctx = cnv.getContext('2d');
+      ctx.drawImage(frame, 0, 0);
+    }
+
     async function main(arg) {
       const width = 640;
       const height = 480;
@@ -21,7 +26,7 @@
 
       const encoder_config = {
         codec: arg.codec,
-        hardwareAcceleration: acceleration,
+        hardwareAcceleration: arg.acceleration,
         width: width,
         height: height,
         bitrate: 5000000,
@@ -39,6 +44,15 @@
 
       let decoder = new VideoDecoder({
         output(frame) {
+          let dots = frames_decoded;
+          // Check that we have intended number of dots and no more.
+          // Completely black frame shouldn't pass the test.
+          if(!validateBlackDots(frame, dots) ||
+            validateBlackDots(frame, dots + 1)) {
+            showFrameForDebug(frame);
+            TEST.reportFailure(
+                `Unexpected dot count ts:${frame.timestamp} dots:${dots}`);
+          }
           frames_decoded++;
           frame.close();
         },
@@ -54,9 +68,6 @@
         output(chunk, metadata) {
           let config = metadata.decoderConfig;
           if (config) {
-            // Here we assume that if accelerated encoding is supported,
-            // accelerated decoding should be supported too.
-            config.hardwareAcceleration = acceleration;
             decoder.configure(config);
           }
           decoder.decode(chunk);
@@ -76,7 +87,12 @@
 
       let encoder = new VideoEncoder(encoder_init);
       encoder.configure(encoder_config);
-      let source = new CanvasSource(width, height);
+
+      let source = await createFrameSource(arg.source_type, width, height);
+      if (!source) {
+        TEST.skip('Unsupported source: ' + arg.source_type);
+        return;
+      }
 
       for (let i = 0; i < frames_to_encode; i++) {
         let frame = await source.getNextFrame();
@@ -106,6 +122,7 @@
 </head>
 
 <body>
+  <canvas id="debug_cnv" width="640" height="480"></canvas>
 </body>
 
 </html>
\ No newline at end of file
diff --git a/content/test/data/gpu/webcodecs/webcodecs_common.js b/content/test/data/gpu/webcodecs/webcodecs_common.js
index 532b98fb9f8d39..bffd6aa7a07340 100644
--- a/content/test/data/gpu/webcodecs/webcodecs_common.js
+++ b/content/test/data/gpu/webcodecs/webcodecs_common.js
@@ -22,6 +22,7 @@ class TestHarness {
   reportSuccess() {
     this.finished = true;
     this.success = true;
+    this.log('Test completed');
   }
 
   reportFailure(error) {
@@ -329,7 +330,7 @@ function createCanvasCaptureSource(width, height) {
 async function prepareDecoderSource(
     frames_to_encode, width, height, codec, acceleration) {
   if (!acceleration)
-    acceleration = 'allow';
+    acceleration = 'no-preference';
   const encoder_config = {
     codec: codec,
     width: width,
diff --git a/content/test/gpu/gpu_tests/test_expectations/webcodecs_expectations.txt b/content/test/gpu/gpu_tests/test_expectations/webcodecs_expectations.txt
index e94f7645496484..7dfbfbf87b96c9 100644
--- a/content/test/gpu/gpu_tests/test_expectations/webcodecs_expectations.txt
+++ b/content/test/gpu/gpu_tests/test_expectations/webcodecs_expectations.txt
@@ -90,6 +90,10 @@ crbug.com/1311091 WebCodecs_WebRTCPeerConnection_* [ Skip ]
 
 crbug.com/1338968 [ android android-nexus-5x ] WebCodecs_TexImage2d_hw_decoder [ Failure ]
 
+# Conservatively expect all macs to fail, I'm not sure if our try bots run arm64
+# devices. A later commit needs to put mac-x86_64 here, or better still fix the
+# bug and remove this expectation.
+crbug.com/1371749 [ mac ] WebCodecs_EncodeDecode_offscreen_avc1.42001E_prefer-hardware [ Failure ]
 #######################################################################
 # Automated Entries After This Point - Do Not Manually Add Below Here #
 #######################################################################
diff --git a/content/test/gpu/gpu_tests/webcodecs_integration_test.py b/content/test/gpu/gpu_tests/webcodecs_integration_test.py
index 77edd24d719edf..14168812723486 100644
--- a/content/test/gpu/gpu_tests/webcodecs_integration_test.py
+++ b/content/test/gpu/gpu_tests/webcodecs_integration_test.py
@@ -102,11 +102,16 @@ def GenerateVideoTests(cls) -> ct.TestGenerator:
                'use_worker': True
            }])
 
-    for codec in video_codecs:
-      yield ('WebCodecs_EncodeDecode_' + codec, 'encode-decode.html', [{
-          'codec':
-          codec
-      }])
+    for source_type in ['offscreen', 'arraybuffer']:
+      for codec in video_codecs:
+        for acc in accelerations:
+          args = (source_type, codec, acc)
+          yield ('WebCodecs_EncodeDecode_%s_%s_%s' % args, 'encode-decode.html',
+                 [{
+                     'source_type': source_type,
+                     'codec': codec,
+                     'acceleration': acc
+                 }])
 
     for source_type in frame_sources:
       for codec in video_codecs:
