/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.provide('shaka.media.PresentationTimeline');
goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.media.SegmentReference');
/**
* PresentationTimeline.
* @export
*/
shaka.media.PresentationTimeline = class {
/**
* @param {?number} presentationStartTime The wall-clock time, in seconds,
* when the presentation started or will start. Only required for live.
* @param {number} presentationDelay The delay to give the presentation, in
* seconds. Only required for live.
* @param {boolean=} autoCorrectDrift Whether to account for drift when
* determining the availability window.
*
* @see {shaka.extern.Manifest}
* @see {@tutorial architecture}
*/
constructor(presentationStartTime, presentationDelay,
autoCorrectDrift = true) {
/** @private {?number} */
this.presentationStartTime_ = presentationStartTime;
/** @private {number} */
this.presentationDelay_ = presentationDelay;
/** @private {number} */
this.duration_ = Infinity;
/** @private {number} */
this.segmentAvailabilityDuration_ = Infinity;
/**
* The maximum segment duration (in seconds). Can be based on explicitly-
* known segments or on signalling in the manifest.
*
* @private {number}
*/
this.maxSegmentDuration_ = 1;
/**
* The minimum segment start time (in seconds, in the presentation timeline)
* for segments we explicitly know about.
*
* This is null if we have no explicit descriptions of segments, such as in
* DASH when using SegmentTemplate w/ duration.
*
* @private {?number}
*/
this.minSegmentStartTime_ = null;
/**
* The maximum segment end time (in seconds, in the presentation timeline)
* for segments we explicitly know about.
*
* This is null if we have no explicit descriptions of segments, such as in
* DASH when using SegmentTemplate w/ duration. When this is non-null, the
* presentation start time is calculated from the segment end times.
*
* @private {?number}
*/
this.maxSegmentEndTime_ = null;
/** @private {number} */
this.clockOffset_ = 0;
/** @private {boolean} */
this.static_ = true;
/** @private {number} */
this.userSeekStart_ = 0;
/** @private {boolean} */
this.autoCorrectDrift_ = autoCorrectDrift;
}
/**
* @return {number} The presentation's duration in seconds.
* Infinity indicates that the presentation continues indefinitely.
* @export
*/
getDuration() {
return this.duration_;
}
/**
* @return {number} The presentation's max segment duration in seconds.
* @export
*/
getMaxSegmentDuration() {
return this.maxSegmentDuration_;
}
/**
* Sets the presentation's duration.
*
* @param {number} duration The presentation's duration in seconds.
* Infinity indicates that the presentation continues indefinitely.
* @export
*/
setDuration(duration) {
goog.asserts.assert(duration > 0, 'duration must be > 0');
this.duration_ = duration;
}
/**
* @return {?number} The presentation's start time in seconds.
* @export
*/
getPresentationStartTime() {
return this.presentationStartTime_;
}
/**
* Sets the clock offset, which is the difference between the client's clock
* and the server's clock, in milliseconds (i.e., serverTime = Date.now() +
* clockOffset).
*
* @param {number} offset The clock offset, in ms.
* @export
*/
setClockOffset(offset) {
this.clockOffset_ = offset;
}
/**
* Sets the presentation's static flag.
*
* @param {boolean} isStatic If true, the presentation is static, meaning all
* segments are available at once.
* @export
*/
setStatic(isStatic) {
// NOTE: the argument name is not "static" because that's a keyword in ES6
this.static_ = isStatic;
}
/**
* Sets the presentation's segment availability duration. The segment
* availability duration should only be set for live.
*
* @param {number} segmentAvailabilityDuration The presentation's new segment
* availability duration in seconds.
* @export
*/
setSegmentAvailabilityDuration(segmentAvailabilityDuration) {
goog.asserts.assert(segmentAvailabilityDuration >= 0,
'segmentAvailabilityDuration must be >= 0');
this.segmentAvailabilityDuration_ = segmentAvailabilityDuration;
}
/**
* Sets the presentation delay in seconds.
*
* @param {number} delay
* @export
*/
setDelay(delay) {
// NOTE: This is no longer used internally, but is exported.
// So we cannot remove it without deprecating it and waiting one release
// cycle, or else we risk breaking custom manifest parsers.
goog.asserts.assert(delay >= 0, 'delay must be >= 0');
this.presentationDelay_ = delay;
}
/**
* Gets the presentation delay in seconds.
* @return {number}
* @export
*/
getDelay() {
return this.presentationDelay_;
}
/**
* Gives PresentationTimeline a Stream's segments so it can size and position
* the segment availability window, and account for missing segment
* information. This function should be called once for each Stream (no more,
* no less).
*
* @param {!Array.<!shaka.media.SegmentReference>} references
* @export
*/
notifySegments(references) {
if (references.length == 0) {
return;
}
const firstReferenceStartTime = references[0].startTime;
const lastReferenceEndTime = references[references.length - 1].endTime;
this.notifyMinSegmentStartTime(firstReferenceStartTime);
this.maxSegmentDuration_ = references.reduce(
(max, r) => { return Math.max(max, r.endTime - r.startTime); },
this.maxSegmentDuration_);
this.maxSegmentEndTime_ =
Math.max(this.maxSegmentEndTime_, lastReferenceEndTime);
if (this.presentationStartTime_ != null && this.autoCorrectDrift_) {
// Since we have explicit segment end times, calculate a presentation
// start based on them. This start time accounts for drift.
// Date.now() is in milliseconds, from which we compute "now" in seconds.
const now = (Date.now() + this.clockOffset_) / 1000.0;
this.presentationStartTime_ =
now - this.maxSegmentEndTime_ - this.maxSegmentDuration_;
}
shaka.log.v1('notifySegments:',
'maxSegmentDuration=' + this.maxSegmentDuration_);
}
/**
* Gives PresentationTimeline a Stream's minimum segment start time.
*
* @param {number} startTime
* @export
*/
notifyMinSegmentStartTime(
startTime) {
if (this.minSegmentStartTime_ == null) {
// No data yet, and Math.min(null, startTime) is always 0. So just store
// startTime.
this.minSegmentStartTime_ = startTime;
} else {
this.minSegmentStartTime_ =
Math.min(this.minSegmentStartTime_, startTime);
}
}
/**
* Gives PresentationTimeline a Stream's maximum segment duration so it can
* size and position the segment availability window. This function should be
* called once for each Stream (no more, no less), but does not have to be
* called if notifySegments() is called instead for a particular stream.
*
* @param {number} maxSegmentDuration The maximum segment duration for a
* particular stream.
* @export
*/
notifyMaxSegmentDuration(maxSegmentDuration) {
this.maxSegmentDuration_ = Math.max(
this.maxSegmentDuration_, maxSegmentDuration);
shaka.log.v1('notifyNewSegmentDuration:',
'maxSegmentDuration=' + this.maxSegmentDuration_);
}
/**
* Offsets the segment times by the given amount.
*
* @param {number} offset The number of seconds to offset by. A positive
* number adjusts the segment times forward.
* @export
*/
offset(offset) {
if (this.minSegmentStartTime_ != null) {
this.minSegmentStartTime_ += offset;
}
if (this.maxSegmentEndTime_ != null) {
this.maxSegmentEndTime_ += offset;
}
}
/**
* @return {boolean} True if the presentation is live; otherwise, return
* false.
* @export
*/
isLive() {
return this.duration_ == Infinity &&
!this.static_;
}
/**
* @return {boolean} True if the presentation is in progress (meaning not
* live, but also not completely available); otherwise, return false.
* @export
*/
isInProgress() {
return this.duration_ != Infinity &&
!this.static_;
}
/**
* Gets the presentation's current segment availability start time. Segments
* ending at or before this time should be assumed to be unavailable.
*
* @return {number} The current segment availability start time, in seconds,
* relative to the start of the presentation.
* @export
*/
getSegmentAvailabilityStart() {
goog.asserts.assert(this.segmentAvailabilityDuration_ >= 0,
'The availability duration should be positive');
const end = this.getSegmentAvailabilityEnd();
const start = end - this.segmentAvailabilityDuration_;
return Math.max(this.userSeekStart_, start);
}
/**
* Sets the start time of the user-defined seek range. This is only used for
* VOD content.
*
* @param {number} time
* @export
*/
setUserSeekStart(time) {
this.userSeekStart_ = time;
}
/**
* Gets the presentation's current segment availability end time. Segments
* starting after this time should be assumed to be unavailable.
*
* @return {number} The current segment availability end time, in seconds,
* relative to the start of the presentation. Always returns the
* presentation's duration for video-on-demand.
* @export
*/
getSegmentAvailabilityEnd() {
if (!this.isLive() && !this.isInProgress()) {
// It's a static manifest (can also be a dynamic->static conversion)
return this.maxSegmentEndTime_ || this.duration_;
}
// Can be either live or "in-progress recording" (live with known duration)
return Math.min(this.getLiveEdge_(), this.duration_);
}
/**
* Gets the seek range start time, offset by the given amount. This is used
* to ensure that we don't "fall" back out of the seek window while we are
* buffering.
*
* @param {number} offset The offset to add to the start time for live
* streams.
* @return {number} The current seek start time, in seconds, relative to the
* start of the presentation.
* @export
*/
getSafeSeekRangeStart(offset) {
// The earliest known segment time, ignoring segment availability duration.
const earliestSegmentTime =
Math.max(this.minSegmentStartTime_, this.userSeekStart_);
// For VOD, the offset and end time are ignored, and we just return the
// earliest segment time. All segments are "safe" in VOD. However, we
// should round up to the nearest millisecond to avoid issues like
// https://github.com/google/shaka-player/issues/2831, in which we tried to
// seek repeatedly to catch up to the seek range, and never actually
// "arrived" within it. The video's currentTime is not as accurate as the
// JS number representing the earliest segment time for some content.
if (this.segmentAvailabilityDuration_ == Infinity) {
return Math.ceil(earliestSegmentTime * 1e3) / 1e3;
}
// AKA the live edge for live streams.
const availabilityEnd = this.getSegmentAvailabilityEnd();
// The ideal availability start, not considering known segments.
const availabilityStart =
availabilityEnd - this.segmentAvailabilityDuration_;
// Add the offset to the availability start to ensure that we don't fall
// outside the availability window while we buffer; we don't need to add the
// offset to earliestSegmentTime since that won't change over time.
// Also see: https://github.com/google/shaka-player/issues/692
const desiredStart =
Math.min(availabilityStart + offset, this.getSeekRangeEnd());
return Math.max(earliestSegmentTime, desiredStart);
}
/**
* Gets the seek range start time.
*
* @return {number}
* @export
*/
getSeekRangeStart() {
return this.getSafeSeekRangeStart(/* offset= */ 0);
}
/**
* Gets the seek range end.
*
* @return {number}
* @export
*/
getSeekRangeEnd() {
const useDelay = this.isLive() || this.isInProgress();
const delay = useDelay ? this.presentationDelay_ : 0;
return Math.max(0, this.getSegmentAvailabilityEnd() - delay);
}
/**
* True if the presentation start time is being used to calculate the live
* edge.
* Using the presentation start time means that the stream may be subject to
* encoder drift. At runtime, we will avoid using the presentation start time
* whenever possible.
*
* @return {boolean}
* @export
*/
usingPresentationStartTime() {
// If it's VOD, IPR, or an HLS "event", we are not using the presentation
// start time.
if (this.presentationStartTime_ == null) {
return false;
}
// If we have explicit segment times, we're not using the presentation
// start time.
if (this.maxSegmentEndTime_ != null && this.autoCorrectDrift_) {
return false;
}
return true;
}
/**
* @return {number} The current presentation time in seconds.
* @private
*/
getLiveEdge_() {
goog.asserts.assert(this.presentationStartTime_ != null,
'Cannot compute timeline live edge without start time');
// Date.now() is in milliseconds, from which we compute "now" in seconds.
const now = (Date.now() + this.clockOffset_) / 1000.0;
return Math.max(
0, now - this.maxSegmentDuration_ - this.presentationStartTime_);
}
/**
* Debug only: assert that the timeline parameters make sense for the type
* of presentation (VOD, IPR, live).
*/
assertIsValid() {
if (goog.DEBUG) {
if (this.isLive()) {
// Implied by isLive(): infinite and dynamic.
// Live streams should have a start time.
goog.asserts.assert(this.presentationStartTime_ != null,
'Detected as live stream, but does not match our model of live!');
} else if (this.isInProgress()) {
// Implied by isInProgress(): finite and dynamic.
// IPR streams should have a start time, and segments should not expire.
goog.asserts.assert(this.presentationStartTime_ != null &&
this.segmentAvailabilityDuration_ == Infinity,
'Detected as IPR stream, but does not match our model of IPR!');
} else { // VOD
// VOD segments should not expire and the presentation should be finite
// and static.
goog.asserts.assert(this.segmentAvailabilityDuration_ == Infinity &&
this.duration_ != Infinity &&
this.static_,
'Detected as VOD stream, but does not match our model of VOD!');
}
}
}
};