Bug 1936352 - VideoEncoder: Return unsupported for codec strings with spaces r=media-playback-reviewers,alwu

This patch fixes a crash that occurs when a codec string with leading
spaces is passed to `VideoEncoder::IsConfigSupported`.

The crash happens because `VideoEncoderConfigInternal::ToEncoderConfig`
assumes that its codec string member begins with a supported codec name
(which should be non-space character). When the codec string has leading
spaces, this assumption is invalidated, leading to a crash.

To resolve this issue, the patch removes the space-trimming in
`CanEncode` and calling `IsSupportedVideoCodec` with the given codec
string directly before `ToEncoderConfig`. By doing so, codec strings
with leading spaces are correctly identified as "unsupported", and
`ToEncoderConfig` is not invoked with invalid input, preventing the
crash.

Additionally, this patch adds a WPT to ensure that codec string
containing spaces are reported as "unsupported" and the no crash occurs
when such strings are processed.

Differential Revision: https://phabricator.services.mozilla.com/D231719

dom/media/webcodecs/VideoEncoder.cpp

@@ -337,13 +337,11 @@ VideoEncoderConfigInternal::Diff(
 
 // https://w3c.github.io/webcodecs/#check-configuration-support
 static bool CanEncode(const RefPtr<VideoEncoderConfigInternal>& aConfig) {
-  auto parsedCodecString =
-      ParseCodecString(aConfig->mCodec).valueOr(EmptyString());
   // TODO: Enable WebCodecs on Android (Bug 1840508)
   if (IsOnAndroid()) {
     return false;
   }
-  if (!IsSupportedVideoCodec(parsedCodecString)) {
+  if (!IsSupportedVideoCodec(aConfig->mCodec)) {
     return false;
   }
   if (aConfig->mScalabilityMode.isSome()) {
@@ -352,7 +350,7 @@ static bool CanEncode(const RefPtr<VideoEncoderConfigInternal>& aConfig) {
         !aConfig->mScalabilityMode->EqualsLiteral("L1T3")) {
       LOGE("Scalability mode %s not supported for codec: %s",
            NS_ConvertUTF16toUTF8(aConfig->mScalabilityMode.value()).get(),
-           NS_ConvertUTF16toUTF8(parsedCodecString).get());
+           NS_ConvertUTF16toUTF8(aConfig->mCodec).get());
       return false;
     }
   }

testing/web-platform/tests/webcodecs/video-encoder-config.https.any.js

@@ -183,6 +183,14 @@ const validButUnsupportedConfigs = [
       height: 480,
     },
   },
+  {
+    comment: 'codec with spaces',
+    config: {
+      codec: '  vp09.00.10.08  ',
+      width: 640,
+      height: 480,
+    }
+  }
 ];
 
 validButUnsupportedConfigs.forEach(entry => {