/**
* @file playlist.js
*
* Playlist related utilities.
*/
import {createTimeRange} from 'video.js';
import window from 'global/window';
let Playlist = {
/**
* The number of segments that are unsafe to start playback at in
* a live stream. Changing this value can cause playback stalls.
* See HTTP Live Streaming, "Playing the Media Playlist File"
* https://tools.ietf.org/html/draft-pantos-http-live-streaming-18#section-6.3.3
*/
UNSAFE_LIVE_SEGMENTS: 3
};
/**
* walk backward until we find a duration we can use
* or return a failure
*
* @param {Playlist} playlist the playlist to walk through
* @param {Number} endSequence the mediaSequence to stop walking on
*/
const backwardDuration = function(playlist, endSequence) {
let result = 0;
let i = endSequence - playlist.mediaSequence;
// if a start time is available for segment immediately following
// the interval, use it
let segment = playlist.segments[i];
// Walk backward until we find the latest segment with timeline
// information that is earlier than endSequence
if (segment) {
if (typeof segment.start !== 'undefined') {
return { result: segment.start, precise: true };
}
if (typeof segment.end !== 'undefined') {
return {
result: segment.end - segment.duration,
precise: true
};
}
}
while (i--) {
segment = playlist.segments[i];
if (typeof segment.end !== 'undefined') {
return { result: result + segment.end, precise: true };
}
result += segment.duration;
if (typeof segment.start !== 'undefined') {
return { result: result + segment.start, precise: true };
}
}
return { result, precise: false };
};
/**
* walk forward until we find a duration we can use
* or return a failure
*
* @param {Playlist} playlist the playlist to walk through
* @param {Number} endSequence the mediaSequence to stop walking on
*/
const forwardDuration = function(playlist, endSequence) {
let result = 0;
let segment;
let i = endSequence - playlist.mediaSequence;
// Walk forward until we find the earliest segment with timeline
// information
for (; i < playlist.segments.length; i++) {
segment = playlist.segments[i];
if (typeof segment.start !== 'undefined') {
return {
result: segment.start - result,
precise: true
};
}
result += segment.duration;
if (typeof segment.end !== 'undefined') {
return {
result: segment.end - result,
precise: true
};
}
}
// indicate we didn't find a useful duration estimate
return { result: -1, precise: false };
};
/**
* Calculate the media duration from the segments associated with a
* playlist. The duration of a subinterval of the available segments
* may be calculated by specifying an end index.
*
* @param {Object} playlist a media playlist object
* @param {Number=} endSequence an exclusive upper boundary
* for the playlist. Defaults to playlist length.
* @param {Number} expired the amount of time that has dropped
* off the front of the playlist in a live scenario
* @return {Number} the duration between the first available segment
* and end index.
*/
const intervalDuration = function(playlist, endSequence, expired) {
let backward;
let forward;
if (typeof endSequence === 'undefined') {
endSequence = playlist.mediaSequence + playlist.segments.length;
}
if (endSequence < playlist.mediaSequence) {
return 0;
}
// do a backward walk to estimate the duration
backward = backwardDuration(playlist, endSequence);
if (backward.precise) {
// if we were able to base our duration estimate on timing
// information provided directly from the Media Source, return
// it
return backward.result;
}
// walk forward to see if a precise duration estimate can be made
// that way
forward = forwardDuration(playlist, endSequence);
if (forward.precise) {
// we found a segment that has been buffered and so it's
// position is known precisely
return forward.result;
}
// return the less-precise, playlist-based duration estimate
return backward.result + expired;
};
/**
* Calculates the duration of a playlist. If a start and end index
* are specified, the duration will be for the subset of the media
* timeline between those two indices. The total duration for live
* playlists is always Infinity.
*
* @param {Object} playlist a media playlist object
* @param {Number=} endSequence an exclusive upper
* boundary for the playlist. Defaults to the playlist media
* sequence number plus its length.
* @param {Number=} expired the amount of time that has
* dropped off the front of the playlist in a live scenario
* @return {Number} the duration between the start index and end
* index.
*/
export const duration = function(playlist, endSequence, expired) {
if (!playlist) {
return 0;
}
if (typeof expired !== 'number') {
expired = 0;
}
// if a slice of the total duration is not requested, use
// playlist-level duration indicators when they're present
if (typeof endSequence === 'undefined') {
// if present, use the duration specified in the playlist
if (playlist.totalDuration) {
return playlist.totalDuration;
}
// duration should be Infinity for live playlists
if (!playlist.endList) {
return window.Infinity;
}
}
// calculate the total duration based on the segment durations
return intervalDuration(playlist,
endSequence,
expired);
};
/**
* Calculates the interval of time that is currently seekable in a
* playlist. The returned time ranges are relative to the earliest
* moment in the specified playlist that is still available. A full
* seekable implementation for live streams would need to offset
* these values by the duration of content that has expired from the
* stream.
*
* @param {Object} playlist a media playlist object
* @param {Number=} expired the amount of time that has
* dropped off the front of the playlist in a live scenario
* @return {TimeRanges} the periods of time that are valid targets
* for seeking
*/
export const seekable = function(playlist, expired) {
let start;
let end;
let endSequence;
if (typeof expired !== 'number') {
expired = 0;
}
// without segments, there are no seekable ranges
if (!playlist || !playlist.segments) {
return createTimeRange();
}
// when the playlist is complete, the entire duration is seekable
if (playlist.endList) {
return createTimeRange(0, duration(playlist));
}
// live playlists should not expose three segment durations worth
// of content from the end of the playlist
// https://tools.ietf.org/html/draft-pantos-http-live-streaming-16#section-6.3.3
start = intervalDuration(playlist, playlist.mediaSequence, expired);
endSequence = Math.max(0, playlist.segments.length - Playlist.UNSAFE_LIVE_SEGMENTS);
end = intervalDuration(playlist,
playlist.mediaSequence + endSequence,
expired);
return createTimeRange(start, end);
};
/**
* Determine the index of the segment that contains a specified
* playback position in a media playlist.
*
* @param {Object} playlist the media playlist to query
* @param {Number} time The number of seconds since the earliest
* possible position to determine the containing segment for
* @param {Number=} expired the duration of content, in
* seconds, that has been removed from this playlist because it
* expired
* @return {Number} The number of the media segment that contains
* that time position.
*/
export const getMediaIndexForTime_ = function(playlist, time, expired) {
let i;
let segment;
let originalTime = time;
let numSegments = playlist.segments.length;
let lastSegment = numSegments - 1;
let startIndex;
let endIndex;
let knownStart;
let knownEnd;
if (!playlist) {
return 0;
}
// when the requested position is earlier than the current set of
// segments, return the earliest segment index
if (time < 0) {
return 0;
}
if (time === 0 && !expired) {
return 0;
}
expired = expired || 0;
// find segments with known timing information that bound the
// target time
for (i = 0; i < numSegments; i++) {
segment = playlist.segments[i];
if (segment.end) {
if (segment.end > time) {
knownEnd = segment.end;
endIndex = i;
break;
} else {
knownStart = segment.end;
startIndex = i + 1;
}
}
}
// time was equal to or past the end of the last segment in the playlist
if (startIndex === numSegments) {
return numSegments;
}
// use the bounds we just found and playlist information to
// estimate the segment that contains the time we are looking for
if (typeof startIndex !== 'undefined') {
// We have a known-start point that is before our desired time so
// walk from that point forwards
time = time - knownStart;
for (i = startIndex; i < (endIndex || numSegments); i++) {
segment = playlist.segments[i];
time -= segment.duration;
if (time < 0) {
return i;
}
}
if (i >= endIndex) {
// We haven't found a segment but we did hit a known end point
// so fallback to interpolating between the segment index
// based on the known span of the timeline we are dealing with
// and the number of segments inside that span
return startIndex + Math.floor(
((originalTime - knownStart) / (knownEnd - knownStart)) *
(endIndex - startIndex));
}
// We _still_ haven't found a segment so load the last one
return lastSegment;
} else if (typeof endIndex !== 'undefined') {
// We _only_ have a known-end point that is after our desired time so
// walk from that point backwards
time = knownEnd - time;
for (i = endIndex; i >= 0; i--) {
segment = playlist.segments[i];
time -= segment.duration;
if (time < 0) {
return i;
}
}
// We haven't found a segment so load the first one if time is zero
if (time === 0) {
return 0;
}
return -1;
}
// We known nothing so walk from the front of the playlist,
// subtracting durations until we find a segment that contains
// time and return it
time = time - expired;
if (time < 0) {
return -1;
}
for (i = 0; i < numSegments; i++) {
segment = playlist.segments[i];
time -= segment.duration;
if (time < 0) {
return i;
}
}
// We are out of possible candidates so load the last one...
// The last one is the least likely to overlap a buffer and therefore
// the one most likely to tell us something about the timeline
return lastSegment;
};
Playlist.duration = duration;
Playlist.seekable = seekable;
Playlist.getMediaIndexForTime_ = getMediaIndexForTime_;
// exports
export default Playlist;