From 8e61b8903ef12871d058765a04b7aecb99d321ad Mon Sep 17 00:00:00 2001
From: Stephen DeRosa <stephen.derosa@livekit.io>
Date: Wed, 23 Sep 2026 08:36:30 +0800
Subject: [PATCH] Advertise pass-through video formats without requiring a
 local real encoder

A pre-encoded publisher supplies its own bitstream, so it does not need a
local encoder for its codec. GetSupportedFormats() previously dropped
pass-through formats for codecs no real encoder factory advertised, which
made pre-encoded H.265 publishes fail silently on machines without a
hardware HEVC encoder: H265 never appeared in the SDP offer, the sender
negotiated a different codec, and PassthroughVideoEncoder then rejected
every frame with "frame codec does not match sender codec" while
captureFrame kept reporting frames as accepted.

Advertising the pass-through formats unconditionally is safe because the
pass-through backend is never selected automatically - it is excluded from
automatic fallback and only used on an explicit publish request - and
Create() already fails loudly rather than falling back to a real encoder
for a pre-encoded sender.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .changeset/advertise-passthrough-formats.md |  8 ++++++++
 webrtc-sys/src/video_encoder_factory.cpp    | 22 ++++++++-------------
 2 files changed, 16 insertions(+), 14 deletions(-)
 create mode 100644 .changeset/advertise-passthrough-formats.md

diff --git a/.changeset/advertise-passthrough-formats.md b/.changeset/advertise-passthrough-formats.md
new file mode 100644
index 000000000..6c4cbf436
--- /dev/null
+++ b/.changeset/advertise-passthrough-formats.md
@@ -0,0 +1,8 @@
+---
+webrtc-sys: patch
+libwebrtc: patch
+livekit: patch
+livekit-ffi: patch
+---
+
+Advertise pre-encoded pass-through video formats even when no local encoder implements the codec, so pre-encoded H.265 publishes negotiate on machines without a hardware HEVC encoder.
diff --git a/webrtc-sys/src/video_encoder_factory.cpp b/webrtc-sys/src/video_encoder_factory.cpp
index e18449c87..60695b36a 100644
--- a/webrtc-sys/src/video_encoder_factory.cpp
+++ b/webrtc-sys/src/video_encoder_factory.cpp
@@ -393,25 +393,19 @@ VideoEncoderFactory::InternalFactory::GetSupportedFormats() const {
                    supported_formats.end());
   }
 
-  // The pass-through factory would otherwise advertise codecs no real
-  // encoder implements (e.g. H265 on desktops); a normal session
-  // negotiating such a codec would end up with a sender that cannot create
-  // an encoder. Only advertise pass-through formats for codecs some real
-  // encoder already supports.
-  const size_t real_format_count = formats.size();
+  // Advertise pass-through formats unconditionally: a pre-encoded publisher
+  // supplies its own bitstream, so it must be able to negotiate codecs no
+  // local encoder implements (e.g. H265 on machines without a hardware
+  // encoder). The pass-through backend is never selected automatically (it
+  // is excluded from automatic fallback and only used on an explicit publish
+  // request), and Create() fails loudly rather than falling back when a
+  // pre-encoded sender cannot be built.
   for (const auto& backend_factory : factories_) {
     if (backend_factory.backend != VideoEncoderBackend::PreEncoded) {
       continue;
     }
     for (const auto& format : backend_factory.factory->GetSupportedFormats()) {
-      const bool codec_available = std::any_of(
-          formats.begin(), formats.begin() + real_format_count,
-          [&](const webrtc::SdpVideoFormat& existing) {
-            return IsSameCodecName(existing.name, format.name);
-          });
-      if (codec_available) {
-        formats.push_back(format);
-      }
+      formats.push_back(format);
     }
   }
   return formats;