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make frameRate check configurable on level up/down transitions #7585

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make frameRate check configurable on level up/down transitions #7585

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d6ca2c9
feat(abr): make frameRate check configurable on level up/down transit…
sojeong-hwang Oct 24, 2025
91d6c76
update api.md
sojeong-hwang Oct 24, 2025
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2 changes: 2 additions & 0 deletions api-extractor/report/hls.js.api.md
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,8 @@ export type ABRControllerConfig = {
abrMaxWithRealBitrate: boolean;
maxStarvationDelay: number;
maxLoadingDelay: number;
abrUpSwitchToLowerFrameRateMode: 'block' | 'allow';
abrDownSwitchToHigherFrameRateMode: 'block' | 'allow';
};

// Warning: (ae-missing-release-tag) "AssetListJSON" is part of the package's API, but it is missing a release tag (@alpha, @beta, @public, or @internal)
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4 changes: 4 additions & 0 deletions src/config.ts
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Expand Up @@ -50,6 +50,8 @@ export type ABRControllerConfig = {
abrMaxWithRealBitrate: boolean;
maxStarvationDelay: number;
maxLoadingDelay: number;
abrUpSwitchToLowerFrameRateMode: 'block' | 'allow';
abrDownSwitchToHigherFrameRateMode: 'block' | 'allow';
};

export type BufferControllerConfig = {
Expand Down Expand Up @@ -432,6 +434,8 @@ export const hlsDefaultConfig: HlsConfig = {
abrMaxWithRealBitrate: false, // used by abr-controller
maxStarvationDelay: 4, // used by abr-controller
maxLoadingDelay: 4, // used by abr-controller
abrUpSwitchToLowerFrameRateMode: 'block', // used by abr-controller
abrDownSwitchToHigherFrameRateMode: 'block', // used by abr-controller
minAutoBitrate: 0, // used by hls
emeEnabled: false, // used by eme-controller
widevineLicenseUrl: undefined, // used by eme-controller
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13 changes: 11 additions & 2 deletions src/controller/abr-controller.ts
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Expand Up @@ -813,6 +813,12 @@ class AbrController extends Logger implements AbrComponentAPI {

const ttfbEstimateSec = this.bwEstimator.getEstimateTTFB() / 1000;
const levelsSkipped: number[] = [];

const isUpSwitchToLowerFrameRate =
this.hls.config.abrUpSwitchToLowerFrameRateMode === 'allow';
const isDownSwitchToHigherFrameRate =
this.hls.config.abrDownSwitchToHigherFrameRateMode === 'allow';

for (let i = maxAutoLevel; i >= minAutoLevel; i--) {
const levelInfo = levels[i];
const upSwitch = i > selectionBaseLevel;
Expand Down Expand Up @@ -898,10 +904,13 @@ class AbrController extends Logger implements AbrComponentAPI {
if (
(currentCodecSet && levelInfo.codecSet !== currentCodecSet) ||
(currentVideoRange && levelInfo.videoRange !== currentVideoRange) ||
(upSwitch && currentFrameRate > levelInfo.frameRate) ||
(upSwitch &&
currentFrameRate > levelInfo.frameRate &&
!isUpSwitchToLowerFrameRate) ||
(!upSwitch &&
currentFrameRate > 0 &&
currentFrameRate < levelInfo.frameRate) ||
currentFrameRate < levelInfo.frameRate &&
!isDownSwitchToHigherFrameRate) ||
Comment on lines -901 to +913
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@robwalch robwalch Oct 27, 2025 •
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I don't think unblocking selection behavior via config is a good solution to working around content that does not follow best practices when providing frame rates at various bitrates (an example with 360-720p@30, 1080p@60, and [email protected] was given offline).

First, we could loosen the checks to allow switching between almost identical frame rates. That could allow switching straight to a higher bitrate at 29.997 from 30 fps. There would still be a chance to switch up to 60fps and then not switch up any higher. The user should be presented with the resolution and frame-rates to allow manual override in these cases. Allowing the client to automatically bounce back and forth between rates should be avoided.

Adding a frameRate (preferred) and maxFrameRate options to the videoPreference: VideoSelectionOption config options interface for initial selection and capping would be preferred. You might also consider making capping part of the fps-controller, (see capLevelOnFPSDrop) but that would entail more of a refactor as that controller is meant to limit selection based on performance, not the variant frame-rate. It could do both, or either, if a simple flat capLevelByFrameRate option is preferred.

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@robwalch robwalch Oct 27, 2025

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Suggested-Workaround: If you really want to force hls.js to ignore level frameRate than change the parsed values after playback has started on hls.levels to all be the same. It may seem like a hack, but it's a valid workaround after level.supportedPromise is resolved.

Comment on lines +907 to +913
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@robwalch robwalch Oct 30, 2025

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First, we could loosen the checks to allow switching between almost identical frame rates

Suggested change
(upSwitch &&
currentFrameRate > levelInfo.frameRate &&
!isUpSwitchToLowerFrameRate) ||
(!upSwitch &&
currentFrameRate > 0 &&
currentFrameRate < levelInfo.frameRate) ||
currentFrameRate < levelInfo.frameRate &&
!isDownSwitchToHigherFrameRate) ||
(upSwitch && currentFrameRate > Math.ceil(levelInfo.frameRate)) ||
(!upSwitch &&
currentFrameRate > 0 &&
Math.ceil(currentFrameRate) < levelInfo.frameRate) ||

levelInfo.supportedResult?.decodingInfoResults?.some(
(info) => info.smooth === false,
)
Expand Down
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