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[GStreamer] Auto-detect USAC support via GStreamer registry #1654

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[GStreamer] Auto-detect USAC support via GStreamer registry #1654

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4 changes: 4 additions & 0 deletions Source/WebCore/platform/graphics/gstreamer/GStreamerRegistryScanner.cpp
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Expand Up @@ -499,6 +499,10 @@ void GStreamerRegistryScanner::initializeDecoders(const GStreamerRegistryScanner
// USAC AOT, is not yet widely available enough to be enabled by default.
const char* value = g_getenv("WEBKIT_GST_CAN_PLAY_USAC");
bool canPlayUsac = value && (!g_strcmp0(value, "true") || !g_strcmp0(value, "1"));
if (!value) {
// Env is not set. Fall back to gst elements query
canPlayUsac = factories.hasElementForMediaType(ElementFactories::Type::AudioDecoder, "audio/mpeg, mpegversion=(int)4, stream-format=(string)usac"_s).isSupported;
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@ntrrgc ntrrgc May 5, 2026

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What element is this?

I think a change like this can be upstreamed, but given the unusual -- and likely problematic -- value for stream-format, I think it's best if we leave a comment mentioning it by name, so that next time we know why this check is there and don't accidentally remove it.

I also noticed that in previous messages, and in the commit message you said "audio sinks" but the check is for an audio decoder. Was that a mistake or does the element in question happen to be both a decoder a sink element (which is possible, depending how the hardware platform API works)?

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@asurdej-comcast asurdej-comcast May 5, 2026

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This is Amlogic "amlhalasink" element that is both decoder and sink. The commit message is misleading indeed

amlhalasink:   Long-name                AmlHalAsink
amlhalasink:   Klass                    Decoder/Sink/Audio
...
amlhalasink: Pad Templates:
amlhalasink:   SINK template: 'sink'
amlhalasink:     Availability: Always
amlhalasink:     Capabilities:
...
amlhalasink:       audio/x-ac4
amlhalasink:       audio/mpeg
amlhalasink:             mpegversion: 4
amlhalasink:           stream-format: { (string)loas, (string)usac }

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@asurdej-comcast asurdej-comcast May 5, 2026

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the same with MediaTek audio sink "mtkaudiosink" which is also decoder and sink at once

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@ntrrgc ntrrgc May 5, 2026

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the same with MediaTek

So both amlhalasink and mtkaudiosink report support for stream-format=usac?

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yes, they both do that actually but it's not a coincidence because mtk had been adjusted for our needs based on amlogic version kind of. So possibly that's why they use the same approach

}
if (canPlayUsac)
m_decoderCodecMap.add("mp4a.40.42"_s, result); // MPEG-4 Extended HE-AAC and xHE-AAC (USAC AOT)
}
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