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L2A fixes #4195

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merged 6 commits into from
Jun 19, 2023
Merged

L2A fixes #4195

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837cffd
Added check for a new segment URL before (re)running L2A algorithm
piersoh May 30, 2023
8940b00
Added check to skip L2A algo with Init segments
piersoh May 30, 2023
09e7708
Merge branch 'Dash-Industry-Forum:development' into L2A-fixes
piersoh May 31, 2023
60de120
Merge branch 'development' into L2A-fixes
piersoh Jun 1, 2023
cedb028
Merge branch 'development' into L2A-fixes
piersoh Jun 19, 2023
0c1efb5
Updated to address Daniel's suggestions
piersoh Jun 19, 2023
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80 changes: 46 additions & 34 deletions src/streaming/rules/abr/L2ARule.js
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Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,7 @@ function L2ARule(config) {
l2AState.lastSegmentDurationS = NaN;
l2AState.lastSegmentRequestTimeMs = NaN;
l2AState.lastSegmentFinishTimeMs = NaN;
l2AState.lastSegmentUrl = '';
}


Expand Down Expand Up @@ -388,56 +389,67 @@ function L2ARule(config) {
let throughputMeasureTime = dashMetrics.getCurrentHttpRequest(mediaType).trace.reduce((a, b) => a + b.d, 0);
const downloadBytes = dashMetrics.getCurrentHttpRequest(mediaType).trace.reduce((a, b) => a + b.b[0], 0);
let lastthroughput = Math.round((8 * downloadBytes) / throughputMeasureTime); // bits/ms = kbits/s
let currentHttpRequest = dashMetrics.getCurrentHttpRequest(mediaType);

if (lastthroughput < 1) {
lastthroughput = 1;
}//To avoid division with 0 (avoid infinity) in case of an absolute network outage

let V = l2AState.lastSegmentDurationS;
let sign = 1;
// Note that for SegmentBase addressing the request url does not change.
// As this is not relevant for low latency streaming at this point the check below is sufficient
if (currentHttpRequest.url === l2AState.lastSegmentUrl ||
currentHttpRequest.type === HTTPRequest.INIT_SEGMENT_TYPE) {
// No change to inputs or init segment so use previously calculated quality
quality = l2AState.lastQuality;

//Main adaptation logic of L2A-LL
for (let i = 0; i < bitrateCount; ++i) {
bitrates[i] = bitrates[i] / 1000; // Originally in bps, now in Kbps
if (currentPlaybackRate * bitrates[i] > lastthroughput) {// In this case buffer would deplete, leading to a stall, which increases latency and thus the particular probability of selsection of bitrate[i] should be decreased.
sign = -1;
} else { // Recalculate Q

let V = l2AState.lastSegmentDurationS;
let sign = 1;

//Main adaptation logic of L2A-LL
for (let i = 0; i < bitrateCount; ++i) {
bitrates[i] = bitrates[i] / 1000; // Originally in bps, now in Kbps
if (currentPlaybackRate * bitrates[i] > lastthroughput) {// In this case buffer would deplete, leading to a stall, which increases latency and thus the particular probability of selsection of bitrate[i] should be decreased.
sign = -1;
}
// The objective of L2A is to minimize the overall latency=request-response time + buffer length after download+ potential stalling (if buffer less than chunk downlad time)
l2AParameter.w[i] = l2AParameter.prev_w[i] + sign * (V / (2 * alpha)) * ((l2AParameter.Q + vl) * (currentPlaybackRate * bitrates[i] / lastthroughput));//Lagrangian descent
}
// The objective of L2A is to minimize the overall latency=request-response time + buffer length after download+ potential stalling (if buffer less than chunk downlad time)
l2AParameter.w[i] = l2AParameter.prev_w[i] + sign * (V / (2 * alpha)) * ((l2AParameter.Q + vl) * (currentPlaybackRate * bitrates[i] / lastthroughput));//Lagrangian descent
}

// Apply euclidean projection on w to ensure w expresses a probability distribution
l2AParameter.w = euclideanProjection(l2AParameter.w);
// Apply euclidean projection on w to ensure w expresses a probability distribution
l2AParameter.w = euclideanProjection(l2AParameter.w);

for (let i = 0; i < bitrateCount; ++i) {
diff1[i] = l2AParameter.w[i] - l2AParameter.prev_w[i];
l2AParameter.prev_w[i] = l2AParameter.w[i];
}
for (let i = 0; i < bitrateCount; ++i) {
diff1[i] = l2AParameter.w[i] - l2AParameter.prev_w[i];
l2AParameter.prev_w[i] = l2AParameter.w[i];
}

// Lagrangian multiplier Q calculation:
l2AParameter.Q = Math.max(0, l2AParameter.Q - V + V * currentPlaybackRate * ((_dotmultiplication(bitrates, l2AParameter.prev_w) + _dotmultiplication(bitrates, diff1)) / lastthroughput));
// Lagrangian multiplier Q calculation:
l2AParameter.Q = Math.max(0, l2AParameter.Q - V + V * currentPlaybackRate * ((_dotmultiplication(bitrates, l2AParameter.prev_w) + _dotmultiplication(bitrates, diff1)) / lastthroughput));

// Quality is calculated as argmin of the absolute difference between available bitrates (bitrates[i]) and bitrate estimation (dotmultiplication(w,bitrates)).
let temp = [];
for (let i = 0; i < bitrateCount; ++i) {
temp[i] = Math.abs(bitrates[i] - _dotmultiplication(l2AParameter.w, bitrates));
}
// Quality is calculated as argmin of the absolute difference between available bitrates (bitrates[i]) and bitrate estimation (dotmultiplication(w,bitrates)).
let temp = [];
for (let i = 0; i < bitrateCount; ++i) {
temp[i] = Math.abs(bitrates[i] - _dotmultiplication(l2AParameter.w, bitrates));
}

// Quality is calculated based on the probability distribution w (the output of L2A)
quality = temp.indexOf(Math.min(...temp));
// Quality is calculated based on the probability distribution w (the output of L2A)
quality = temp.indexOf(Math.min(...temp));

// We employ a cautious -stepwise- ascent
if (quality > l2AState.lastQuality) {
if (bitrates[l2AState.lastQuality + 1] <= lastthroughput) {
quality = l2AState.lastQuality + 1;
// We employ a cautious -stepwise- ascent
if (quality > l2AState.lastQuality) {
if (bitrates[l2AState.lastQuality + 1] <= lastthroughput) {
quality = l2AState.lastQuality + 1;
}
}
}

// Provision against bitrate over-estimation, by re-calibrating the Lagrangian multiplier Q, to be taken into account for the next chunk
if (bitrates[quality] >= lastthroughput) {
l2AParameter.Q = react * Math.max(vl, l2AParameter.Q);
// Provision against bitrate over-estimation, by re-calibrating the Lagrangian multiplier Q, to be taken into account for the next chunk
if (bitrates[quality] >= lastthroughput) {
l2AParameter.Q = react * Math.max(vl, l2AParameter.Q);
}
l2AState.lastSegment.url = currentHttpRequest.url;
}

switchRequest.quality = quality;
switchRequest.reason.throughput = throughput;
switchRequest.reason.latency = latency;
Expand Down