Clamp simulcast lower layers to top layer#1084
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Ports the four SimulcastPresetsTests cases that were missing from the initial port: same-resolution full clamp, parameterized ladder length over the < 480 / [480, 960) / >= 960 cutoffs, no-overshoot pass-through, and priority forwarding through the clamp.
Mirrors the Swift guard let lowPreset = presets.first else { return
[baseParameters] } fallback. Unreachable from current call sites since
both default ladders return >= 1 entry, but keeps the function safe
against future callers passing an empty requestedPresets with a default
that could collapse to empty.
Use max/max (preset's larger dimension vs output's larger dimension) to match the Swift Dimensions.encodings(from:) helper and the new _clampSimulcastPreset's scaleDownBy calculation. Equivalent for matching-aspect presets, only differs when a caller mixes a non-matching-aspect preset with the output dimensions.
cloudwebrtc
approved these changes
May 19, 2026
…into hiroshi/clamp-simulcast-layers # Conflicts: # test/utils_test.dart
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Pull request overview
This PR ports simulcast lower-layer clamping behavior to the Flutter SDK so lower simulcast layers can’t exceed the configured top layer in framerate, and only clamp bitrate when the “lower” layer doesn’t actually downscale resolution. It also adjusts how simulcast scale-down factors and ladder length are computed by using the larger output dimension.
Changes:
- Update simulcast encoding scale computation to use the larger dimension (
max) when calculatingscaleResolutionDownBy. - Add
Utils.computeSimulcastPresetsand_clampSimulcastPresetto clamp lower-layer framerate (always) and bitrate (only when no real downscale occurs). - Add/expand tests covering clamping behavior, ladder length selection, unchanged pass-through behavior, priority preservation, and computed RTC encodings.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
lib/src/utils.dart |
Adjusts simulcast scaling calculations and introduces preset computation + clamping logic used by encoding generation. |
test/utils_test.dart |
Adds unit tests validating simulcast preset clamping and encoding computation behavior. |
.changes/clamp-simulcast-lower-layers |
Adds a changelog entry for the simulcast clamping fix. |
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hiroshihorie
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Summary
Testing
dart format --output=none --set-exit-if-changed lib/src/types/video_parameters.dart lib/src/utils.dart test/utils_test.dartflutter test test/utils_test.dartflutter analyze --no-pub lib/src/types/video_parameters.dart lib/src/utils.dart test/utils_test.dart