rx-player
Version:
Canal+ HTML5 Video Player
54 lines (53 loc) • 2.16 kB
JavaScript
;
/**
* Copyright 2015 CANAL+ Group
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
Object.defineProperty(exports, "__esModule", { value: true });
exports.default = getBufferLevels;
/**
* Return "Buffer Levels" which are steps of available buffers from which we
* are normally able switch safely to the next available bitrate.
* (Following an algorithm close to BOLA)
* @param {Array.<number>} bitrates - All available bitrates, __sorted__ in
* ascending order.
* @returns {Array.<number>}
*/
function getBufferLevels(bitrates) {
var logs = bitrates.map(function (b) { return Math.log(b / bitrates[0]); });
var utilities = logs.map(function (l) { return l - logs[0] + 1; }); // normalize
var gp = (utilities[utilities.length - 1] - 1) / (bitrates.length * 2 + 10);
var Vp = 1 / gp;
return bitrates.map(function (_, i) { return minBufferLevelForBitrate(i); });
/**
* Get minimum buffer we should keep ahead to pick this bitrate.
* @param {number} index
* @returns {number}
*/
function minBufferLevelForBitrate(index) {
if (index === 0) {
return 0;
}
var boundedIndex = Math.min(Math.max(1, index), bitrates.length - 1);
if (bitrates[boundedIndex] === bitrates[boundedIndex - 1]) {
return minBufferLevelForBitrate(index - 1);
}
return (Vp *
(gp +
(bitrates[boundedIndex] * utilities[boundedIndex - 1] -
bitrates[boundedIndex - 1] * utilities[boundedIndex]) /
(bitrates[boundedIndex] - bitrates[boundedIndex - 1])) +
4);
}
}