106 lines
3.3 KiB
JavaScript
106 lines
3.3 KiB
JavaScript
var uint8ToCString = require('../utils/string.js').uint8ToCString;
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var getUint64 = require('../utils/numbers.js').getUint64;
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/**
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* Based on: ISO/IEC 23009 Section: 5.10.3.3
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* References:
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* https://dashif-documents.azurewebsites.net/Events/master/event.html#emsg-format
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* https://aomediacodec.github.io/id3-emsg/
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*
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* Takes emsg box data as a uint8 array and returns a emsg box object
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* @param {UInt8Array} boxData data from emsg box
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* @returns A parsed emsg box object
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*/
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var parseEmsgBox = function(boxData) {
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// version + flags
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var offset = 4;
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var version = boxData[0];
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var scheme_id_uri,
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value,
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timescale,
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presentation_time,
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presentation_time_delta,
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event_duration,
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id,
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message_data;
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if (version === 0) {
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scheme_id_uri = uint8ToCString(boxData.subarray(offset));
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offset += scheme_id_uri.length;
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value = uint8ToCString(boxData.subarray(offset));
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offset += value.length;
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var dv = new DataView(boxData.buffer);
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timescale = dv.getUint32(offset);
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offset += 4;
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presentation_time_delta = dv.getUint32(offset);
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offset += 4;
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event_duration = dv.getUint32(offset);
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offset += 4;
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id = dv.getUint32(offset);
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offset += 4;
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} else if (version === 1) {
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var dv = new DataView(boxData.buffer);
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timescale = dv.getUint32(offset);
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offset += 4;
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presentation_time = getUint64(boxData.subarray(offset));
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offset += 8;
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event_duration = dv.getUint32(offset);
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offset += 4;
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id = dv.getUint32(offset);
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offset += 4;
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scheme_id_uri = uint8ToCString(boxData.subarray(offset));
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offset += scheme_id_uri.length;
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value = uint8ToCString(boxData.subarray(offset));
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offset += value.length;
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}
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message_data = new Uint8Array(boxData.subarray(offset, boxData.byteLength));
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var emsgBox = {
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scheme_id_uri,
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value,
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// if timescale is undefined or 0 set to 1
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timescale: timescale ? timescale : 1,
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presentation_time,
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presentation_time_delta,
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event_duration,
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id,
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message_data };
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return isValidEmsgBox(version, emsgBox) ? emsgBox : undefined;
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};
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/**
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* Scales a presentation time or time delta with an offset with a provided timescale
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* @param {number} presentationTime
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* @param {number} timescale
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* @param {number} timeDelta
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* @param {number} offset
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* @returns the scaled time as a number
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*/
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var scaleTime = function(presentationTime, timescale, timeDelta, offset) {
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return presentationTime || presentationTime === 0 ? presentationTime / timescale : offset + timeDelta / timescale;
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};
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/**
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* Checks the emsg box data for validity based on the version
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* @param {number} version of the emsg box to validate
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* @param {Object} emsg the emsg data to validate
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* @returns if the box is valid as a boolean
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*/
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var isValidEmsgBox = function(version, emsg) {
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var hasScheme = emsg.scheme_id_uri !== '\0'
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var isValidV0Box = version === 0 && isDefined(emsg.presentation_time_delta) && hasScheme;
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var isValidV1Box = version === 1 && isDefined(emsg.presentation_time) && hasScheme;
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// Only valid versions of emsg are 0 and 1
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return !(version > 1) && isValidV0Box || isValidV1Box;
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};
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// Utility function to check if an object is defined
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var isDefined = function(data) {
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return data !== undefined || data !== null;
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};
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module.exports = {
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parseEmsgBox: parseEmsgBox,
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scaleTime: scaleTime
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};
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