-
Notifications
You must be signed in to change notification settings - Fork 2.6k
/
fragment-finders.ts
175 lines (164 loc) · 6.39 KB
/
fragment-finders.ts
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
import BinarySearch from '../utils/binary-search';
import { Fragment } from '../loader/fragment';
/**
* Returns first fragment whose endPdt value exceeds the given PDT.
* @param {Array<Fragment>} fragments - The array of candidate fragments
* @param {number|null} [PDTValue = null] - The PDT value which must be exceeded
* @param {number} [maxFragLookUpTolerance = 0] - The amount of time that a fragment's start/end can be within in order to be considered contiguous
* @returns {*|null} fragment - The best matching fragment
*/
export function findFragmentByPDT(
fragments: Array<Fragment>,
PDTValue: number | null,
maxFragLookUpTolerance: number
): Fragment | null {
if (
PDTValue === null ||
!Array.isArray(fragments) ||
!fragments.length ||
!Number.isFinite(PDTValue)
) {
return null;
}
// if less than start
const startPDT = fragments[0].programDateTime;
if (PDTValue < (startPDT || 0)) {
return null;
}
const endPDT = fragments[fragments.length - 1].endProgramDateTime;
if (PDTValue >= (endPDT || 0)) {
return null;
}
maxFragLookUpTolerance = maxFragLookUpTolerance || 0;
for (let seg = 0; seg < fragments.length; ++seg) {
const frag = fragments[seg];
if (pdtWithinToleranceTest(PDTValue, maxFragLookUpTolerance, frag)) {
return frag;
}
}
return null;
}
/**
* Finds a fragment based on the SN of the previous fragment; or based on the needs of the current buffer.
* This method compensates for small buffer gaps by applying a tolerance to the start of any candidate fragment, thus
* breaking any traps which would cause the same fragment to be continuously selected within a small range.
* @param {*} fragPrevious - The last frag successfully appended
* @param {Array} fragments - The array of candidate fragments
* @param {number} [bufferEnd = 0] - The end of the contiguous buffered range the playhead is currently within
* @param {number} maxFragLookUpTolerance - The amount of time that a fragment's start/end can be within in order to be considered contiguous
* @returns {*} foundFrag - The best matching fragment
*/
export function findFragmentByPTS(
fragPrevious: Fragment | null,
fragments: Array<Fragment>,
bufferEnd: number = 0,
maxFragLookUpTolerance: number = 0
): Fragment | null {
let fragNext: Fragment | null = null;
if (fragPrevious) {
fragNext =
fragments[
(fragPrevious.sn as number) - (fragments[0].sn as number) + 1
] || null;
} else if (bufferEnd === 0 && fragments[0].start === 0) {
fragNext = fragments[0];
}
// Prefer the next fragment if it's within tolerance
if (
fragNext &&
fragmentWithinToleranceTest(bufferEnd, maxFragLookUpTolerance, fragNext) ===
0
) {
return fragNext;
}
// We might be seeking past the tolerance so find the best match
const foundFragment = BinarySearch.search(
fragments,
fragmentWithinToleranceTest.bind(null, bufferEnd, maxFragLookUpTolerance)
);
if (foundFragment) {
return foundFragment;
}
// If no match was found return the next fragment after fragPrevious, or null
return fragNext;
}
/**
* The test function used by the findFragmentBySn's BinarySearch to look for the best match to the current buffer conditions.
* @param {*} candidate - The fragment to test
* @param {number} [bufferEnd = 0] - The end of the current buffered range the playhead is currently within
* @param {number} [maxFragLookUpTolerance = 0] - The amount of time that a fragment's start can be within in order to be considered contiguous
* @returns {number} - 0 if it matches, 1 if too low, -1 if too high
*/
export function fragmentWithinToleranceTest(
bufferEnd = 0,
maxFragLookUpTolerance = 0,
candidate: Fragment
) {
// offset should be within fragment boundary - config.maxFragLookUpTolerance
// this is to cope with situations like
// bufferEnd = 9.991
// frag[Ø] : [0,10]
// frag[1] : [10,20]
// bufferEnd is within frag[0] range ... although what we are expecting is to return frag[1] here
// frag start frag start+duration
// |-----------------------------|
// <---> <--->
// ...--------><-----------------------------><---------....
// previous frag matching fragment next frag
// return -1 return 0 return 1
// logger.log(`level/sn/start/end/bufEnd:${level}/${candidate.sn}/${candidate.start}/${(candidate.start+candidate.duration)}/${bufferEnd}`);
// Set the lookup tolerance to be small enough to detect the current segment - ensures we don't skip over very small segments
const candidateLookupTolerance = Math.min(
maxFragLookUpTolerance,
candidate.duration + (candidate.deltaPTS ? candidate.deltaPTS : 0)
);
if (
candidate.start + candidate.duration - candidateLookupTolerance <=
bufferEnd
) {
return 1;
} else if (
candidate.start - candidateLookupTolerance > bufferEnd &&
candidate.start
) {
// if maxFragLookUpTolerance will have negative value then don't return -1 for first element
return -1;
}
return 0;
}
/**
* The test function used by the findFragmentByPdt's BinarySearch to look for the best match to the current buffer conditions.
* This function tests the candidate's program date time values, as represented in Unix time
* @param {*} candidate - The fragment to test
* @param {number} [pdtBufferEnd = 0] - The Unix time representing the end of the current buffered range
* @param {number} [maxFragLookUpTolerance = 0] - The amount of time that a fragment's start can be within in order to be considered contiguous
* @returns {boolean} True if contiguous, false otherwise
*/
export function pdtWithinToleranceTest(
pdtBufferEnd: number,
maxFragLookUpTolerance: number,
candidate: Fragment
): boolean {
const candidateLookupTolerance =
Math.min(
maxFragLookUpTolerance,
candidate.duration + (candidate.deltaPTS ? candidate.deltaPTS : 0)
) * 1000;
// endProgramDateTime can be null, default to zero
const endProgramDateTime = candidate.endProgramDateTime || 0;
return endProgramDateTime - candidateLookupTolerance > pdtBufferEnd;
}
export function findFragWithCC(
fragments: Fragment[],
cc: number
): Fragment | null {
return BinarySearch.search(fragments, (candidate) => {
if (candidate.cc < cc) {
return 1;
} else if (candidate.cc > cc) {
return -1;
} else {
return 0;
}
});
}