Support wider range of H264 `profile-level-id` in `webrtc` by wkazmierczak · Pull Request #1867 · software-mansion/smelter

wkazmierczak · 2026-03-30T16:00:20Z

No description provided.

Copilot

Pull request overview

Extends WebRTC H.264 SDP handling to accept a broader set of offered profile-level-id values, and introduces Vulkan-specific filtering so codec entries can be constrained to GPU capabilities when using Vulkan H.264 encode/decode.

Changes:

Expand advertised H.264 codec parameter variants (profile-level-id list) and generate them programmatically.
Rework H.264 offer filtering to “mirror” offer payload types/fmtp into local codec registrations.
Add a Vulkan capability-based H.264 profile/level filter and wire it into WHIP input and WHEP output paths.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
smelter-core/src/pipeline/webrtc/whip_input/video_preferences.rs	Passes `PipelineCtx` to allow Vulkan H.264 capability filtering for decoder preferences.
smelter-core/src/pipeline/webrtc/whip_input/create_new_session.rs	Updates call site for new `video_params_compliant_with_offer(ctx, ...)` signature.
smelter-core/src/pipeline/webrtc/whep_output/peer_connection.rs	Adds Vulkan H.264 capability filtering for encoder codec registration.
smelter-core/src/pipeline/webrtc/supported_codec_parameters.rs	Broadens H.264 `profile-level-id` coverage and simplifies param generation.
smelter-core/src/pipeline/webrtc/mod.rs	Registers the new Vulkan capability filter module.
smelter-core/src/pipeline/webrtc/h264_vulkan_capability_filter.rs	New module: filters H.264 codec params based on Vulkan max supported level per profile.
smelter-core/src/pipeline/webrtc/h264_offer_filter.rs	Reworks offer filtering to mirror offered H.264 payload types + fmtp constraints.

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

smelter-core/src/pipeline/webrtc/h264_offer_filter.rs

smelter-core/src/pipeline/webrtc/whip_input/video_preferences.rs

Copilot · 2026-03-30T16:07:42Z

smelter-core/src/pipeline/webrtc/whip_input/video_preferences.rs

+    video_preferences
+        .iter()
+        .any(|pref| matches!(pref, VideoDecoderOptions::VulkanH264))


uses_vulkan_h264 enables Vulkan capability filtering if any Vulkan H264 decoder is present in video_preferences. If the preferences include both FfmpegH264 and VulkanH264 (and FFmpeg is ordered first), this will still restrict the advertised/negotiated H264 variants to Vulkan-supported ones, potentially preventing negotiation of profiles that FFmpeg could decode. Consider basing this on the preferred H264 decoder (first occurrence of either H264 option) rather than any().

Suggested change

video_preferences

.iter()

.any(|pref| matches!(pref, VideoDecoderOptions::VulkanH264))

// Determine whether the *preferred* H264 decoder is Vulkan by looking at the

// first occurrence of any H264-related preference.

video_preferences

.iter()

.find(|pref| {

matches!(

pref,

VideoDecoderOptions::FfmpegH264 | VideoDecoderOptions::VulkanH264

)

})

.map_or(false, |pref| matches!(pref, VideoDecoderOptions::VulkanH264))

smelter-core/src/pipeline/webrtc/whep_output/peer_connection.rs

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

vk-video/src/device/caps.rs

Copilot · 2026-03-30T16:33:57Z

smelter-core/src/pipeline/webrtc/h264_offer_filter.rs

+        let mut codec = template.clone();

-            offer_h264_params
-                .iter()
-                .any(|(offer_plid, offer_pmode)| *offer_plid == plid && *offer_pmode == pmode)
-        })
-        .collect()
+        codec.payload_type = offer.payload_type;
+        codec.capability.sdp_fmtp_line = build_h264_fmtp(
+            offer.profile_level_id.as_deref(),
+            offer.packetization_mode.as_str(),
+        );
+        passthrough.push(codec);


This overwrites the registered H264 payload_type with the value from the remote SDP offer. Downstream RTP packetization in this repo sets RTP header payload types explicitly (e.g., Payloader uses PayloaderOptions.payload_type), and parts of the WHEP output path currently initialize payload type to a fixed constant (H264=102). With this change, the negotiated/answered payload type can legitimately differ from 102, so the sender may emit RTP with a payload type that doesn’t match the negotiated SDP. Consider plumbing the negotiated payload type into the payloader (similar to whip_output/setup_track.rs which uses codec_params.payload_type) or otherwise ensuring the RTP payload type matches the negotiated codec.

Copilot · 2026-03-30T16:33:57Z

smelter-core/src/pipeline/webrtc/h264_offer_filter.rs

    let session_description = offer.unmarshal().ok()?;
+    let mut h264_payload_types = HashSet::new();
    let mut params = Vec::new();

    for md in &session_description.media_descriptions {
        if !md.media_name.media.eq_ignore_ascii_case("video") {
            continue;
        }
+
+        for attr in &md.attributes {
+            if !attr.key.eq_ignore_ascii_case("rtpmap") {
+                continue;
+            }
+            let value = attr.value.as_deref().unwrap_or("");
+            let Some((pt, codec_desc)) = value.split_once(' ') else {
+                continue;
+            };
+            let Some(payload_type) = pt.trim().parse::<u8>().ok() else {
+                continue;
+            };
+
+            let codec_name = codec_desc.split('/').next().unwrap_or("");
+            if codec_name.eq_ignore_ascii_case("H264") {
+                h264_payload_types.insert(payload_type);
+            }
+        }


h264_payload_types is accumulated across all video media descriptions, but RTP payload types are scoped per media section (m-line). If an SDP offer contains multiple video m-lines that reuse the same payload numbers for different codecs, this cross-media set can cause fmtp lines from one m-line to be incorrectly treated as H264 based on rtpmap from another. Consider computing the H264 payload-type set per-media-description (move the set inside the for md loop) so rtpmap/fmtp matching stays within the same m-line.

wkazmierczak requested a review from Copilot March 30, 2026 16:02

Copilot started reviewing on behalf of wkazmierczak March 30, 2026 16:02 View session

wkazmierczak marked this pull request as ready for review March 30, 2026 16:02

Copilot AI reviewed Mar 30, 2026

View reviewed changes

Support wider range of h264 profile-level-id

5f5ef07

wkazmierczak force-pushed the @wkazmierczak/webrtc-h264-type-from-offer branch from 5b7837f to 5f5ef07 Compare March 30, 2026 16:14

review changes

a2a0413

wkazmierczak requested a review from Copilot March 30, 2026 16:25

Copilot started reviewing on behalf of wkazmierczak March 30, 2026 16:26 View session

Copilot AI reviewed Mar 30, 2026

View reviewed changes

wip

144eb30

wkazmierczak force-pushed the @wkazmierczak/webrtc-h264-type-from-offer branch from a716f09 to 144eb30 Compare April 3, 2026 10:37

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Support wider range of H264 `profile-level-id` in `webrtc`#1867

Support wider range of H264 `profile-level-id` in `webrtc`#1867
wkazmierczak wants to merge 3 commits intomasterfrom
@wkazmierczak/webrtc-h264-type-from-offer

wkazmierczak commented Mar 30, 2026

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Uh oh!

Copilot AI Mar 30, 2026

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Copilot AI Mar 30, 2026

Uh oh!

Copilot AI Mar 30, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

-    video_preferences
-        .iter()
-        .any(|pref| matches!(pref, VideoDecoderOptions::VulkanH264))
+    // Determine whether the *preferred* H264 decoder is Vulkan by looking at the
+    // first occurrence of any H264-related preference.
+    video_preferences
+        .iter()
+        .find(|pref| {
+            matches!(
+                pref,
+                VideoDecoderOptions::FfmpegH264 | VideoDecoderOptions::VulkanH264
+            )
+        })
+        .map_or(false, |pref| matches!(pref, VideoDecoderOptions::VulkanH264))

Conversation

wkazmierczak commented Mar 30, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Copilot AI Mar 30, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Copilot AI Mar 30, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 30, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants