AbandonRequestRule

Description

During the download of a media segment dash.js receives multiple progress events from the underlying API that is used for downloading the data (e.g. XMLHttpRequest). These events have a timestamp and contain information about the number of bytes that have been received so far. Using this information dash.js decides whether to abort the download of a segment.

The AbandonRequestRule implements the logic to decide whether the download of a media segment shall be aborted. Moreover, the rules decides to which quality to switch in such a scenario. Segment downloads are aborted if the current throughput is not sufficient to finish the download of the current media segment in a “reasonable” time.

For that reason, the AbandonRequestRule calculates the throughput based on the received samples (progress event) from the current media segment. If the remaining download time for the current segment is larger than the current segment duration multiplied by abandonDurationMultiplier and the number of remaining bytes to download is larger than the number of total bytes for the new quality the AbandonRequestRule triggers a switch to a lower quality:

if (estimatedTimeOfDownloadInSeconds < request.duration * settings.get().streaming.abr.rules.abandonRequestsRule.parameters.abandonDurationMultiplier || abrController.isPlayingAtLowestQuality(representation)) {
    return switchRequest;
}

const remainingBytesToDownload = request.bytesTotal - request.bytesLoaded;
const optimalRepresentationForBitrate = abrController.getOptimalRepresentationForBitrate(mediaInfo, throughputInKbit, true);
const totalBytesForOptimalRepresentation = request.bytesTotal * optimalRepresentationForBitrate.bitrateInKbit / currentRequestedRepresentation.bitrateInKbit;

// Switch quality in case there is a Representation that requires less bytes to download
if (remainingBytesToDownload > totalBytesForOptimalRepresentation) {
    switchRequest.representation = optimalRepresentationForBitrate;
    switchRequest.reason = {
        throughputInKbit
    }
    abandonDict[request.index] = true;
    logger.info(`[AbandonRequestRule][${mediaType} is asking to abandon and switch to quality to ${optimalRepresentationForBitrate.absoluteIndex}. The measured bandwidth was ${throughputInKbit} kbit/s`);
}

Configuration Options

Parameter	Description
abandonDurationMultiplier	Factor to multiply with the segment duration to compare against the estimated remaining download time of the current segment. See code example above.
minSegmentDownloadTimeThresholdInMs	The AbandonRequestRule only kicks if the download time of the current segment exceeds this value.
minThroughputSamplesThreshold	Minimum throughput samples (equivalent to number of progress events) required before the AbandonRequestRule kicks in.

Example

player.updateSettings({
    streaming: {
        abr: {
            rules: {
                abandonRequestsRule: {
                    active: true,
                    parameters: {
                        abandonDurationMultiplier: 1.8,
                        minSegmentDownloadTimeThresholdInMs: 500,
                        minThroughputSamplesThreshold: 6
                    }
                }
            }
        }
    }
});