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Only advertise internal H264 decode formats if the decoder works #1313

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Merged
MaxHeimbrock merged 4 commits into from
Aug 5, 2026
Merged

Only advertise internal H264 decode formats if the decoder works #1313

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f0506f8
Only advertise internal H264 decode formats if the decoder works
MaxHeimbrock Aug 4, 2026
3475c50
Gate the internal H264 fallback in Create() on the probe result
MaxHeimbrock Aug 4, 2026
9090990
changeset
MaxHeimbrock Aug 4, 2026
ad71ad1
Address review: const probe flag, rename, per-branch logs, braces
MaxHeimbrock Aug 5, 2026
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8 changes: 8 additions & 0 deletions .changeset/only_advertise_internal_h264_decode_formats_if_the_decoder_w.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
---
libwebrtc: patch
livekit: patch
livekit-ffi: patch
webrtc-sys: patch
---

Only advertise internal H264 decode formats if the decoder works - #1313 (@MaxHeimbrock)
1 change: 1 addition & 0 deletions webrtc-sys/include/livekit/video_decoder_factory.h
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Expand Up @@ -35,5 +35,6 @@ class VideoDecoderFactory : public webrtc::VideoDecoderFactory {

private:
std::vector<std::unique_ptr<webrtc::VideoDecoderFactory>> factories_;
const bool internal_h264_decoder_works_;
};
} // namespace livekit_ffi
48 changes: 43 additions & 5 deletions webrtc-sys/src/video_decoder_factory.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,36 @@

namespace livekit_ffi {

VideoDecoderFactory::VideoDecoderFactory() {
namespace {
// H264Decoder::IsSupported() only reflects the WEBRTC_USE_H264 build flag;
// desktop prebuilts link an FFmpeg without the H.264 codec, which only
// surfaces when Configure() fails at runtime ("FFmpeg H.264 decoder not
// found"). Probe once so the SDP does not advertise decode support the
// internal decoder cannot deliver.
bool IsInternalH264DecoderAvailable() {
if (!webrtc::H264Decoder::IsSupported()) {
RTC_LOG(LS_WARNING) << "Internal H264 decoder not compiled in "
"(WEBRTC_USE_H264 off)";
return false;
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}
auto decoder = webrtc::H264Decoder::Create();
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if (!decoder) {
RTC_LOG(LS_WARNING) << "H264Decoder::Create() returned null";
return false;
}
webrtc::VideoDecoder::Settings settings;
settings.set_codec_type(webrtc::kVideoCodecH264);
if (!decoder->Configure(settings)) {
RTC_LOG(LS_WARNING) << "Internal H264 decoder failed to configure; "
"FFmpeg likely lacks the H.264 codec";
return false;
}
return true;
}
} // namespace

VideoDecoderFactory::VideoDecoderFactory()
: internal_h264_decoder_works_(IsInternalH264DecoderAvailable()) {
#ifdef __APPLE__
factories_.push_back(livekit_ffi::CreateObjCVideoDecoderFactory());
#endif
Expand All @@ -55,6 +84,11 @@ VideoDecoderFactory::VideoDecoderFactory() {
factories_.push_back(std::make_unique<webrtc::NvidiaVideoDecoderFactory>());
}
#endif

if (!internal_h264_decoder_works_) {
RTC_LOG(LS_WARNING) << "Internal H264 decoder is unavailable, "
"not advertising its formats";
}
}

std::vector<webrtc::SdpVideoFormat> VideoDecoderFactory::GetSupportedFormats()
Expand All @@ -71,9 +105,12 @@ std::vector<webrtc::SdpVideoFormat> VideoDecoderFactory::GetSupportedFormats()
for (const webrtc::SdpVideoFormat& format :
webrtc::SupportedVP9DecoderCodecs())
formats.push_back(format);
for (const webrtc::SdpVideoFormat& h264_format :
webrtc::SupportedH264DecoderCodecs())
formats.push_back(h264_format);
if (internal_h264_decoder_works_) {

@MaxHeimbrock MaxHeimbrock Aug 4, 2026 •
edited
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Filter the supported formats based on if a working h264 decoder is present in this lib at runtime.

for (const webrtc::SdpVideoFormat& h264_format :
webrtc::SupportedH264DecoderCodecs()) {
formats.push_back(h264_format);
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}
}

formats.push_back(webrtc::SdpVideoFormat(
webrtc::SdpVideoFormat::AV1Profile0(),
Expand Down Expand Up @@ -131,7 +168,8 @@ std::unique_ptr<webrtc::VideoDecoder> VideoDecoderFactory::Create(
return webrtc::CreateVp8Decoder(env);
if (absl::EqualsIgnoreCase(format.name, webrtc::kVp9CodecName))
return webrtc::VP9Decoder::Create();
if (absl::EqualsIgnoreCase(format.name, webrtc::kH264CodecName))
if (absl::EqualsIgnoreCase(format.name, webrtc::kH264CodecName) &&

@MaxHeimbrock MaxHeimbrock Aug 4, 2026

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If at runtime for whatever reason we try to create the decoder and it is not supported, error

internal_h264_decoder_works_)
return webrtc::H264Decoder::Create();


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