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| 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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 | /**
* Parser for exponential Golomb codes, a variable-bitwidth number encoding scheme used by h264.
*/
import { logger } from '../utils/logger';
class ExpGolomb {
constructor (data) {
this.data = data;
// the number of bytes left to examine in this.data
this.bytesAvailable = data.byteLength;
// the current word being examined
this.word = 0; // :uint
// the number of bits left to examine in the current word
this.bitsAvailable = 0; // :uint
}
// ():void
loadWord () {
let
data = this.data,
bytesAvailable = this.bytesAvailable,
position = data.byteLength - bytesAvailable,
workingBytes = new Uint8Array(4),
availableBytes = Math.min(4, bytesAvailable);
if (availableBytes === 0)
throw new Error('no bytes available');
workingBytes.set(data.subarray(position, position + availableBytes));
this.word = new DataView(workingBytes.buffer).getUint32(0);
// track the amount of this.data that has been processed
this.bitsAvailable = availableBytes * 8;
this.bytesAvailable -= availableBytes;
}
// (count:int):void
skipBits (count) {
let skipBytes; // :int
if (this.bitsAvailable > count) {
this.word <<= count;
this.bitsAvailable -= count;
} else {
count -= this.bitsAvailable;
skipBytes = count >> 3;
count -= (skipBytes >> 3);
this.bytesAvailable -= skipBytes;
this.loadWord();
this.word <<= count;
this.bitsAvailable -= count;
}
}
// (size:int):uint
readBits (size) {
let
bits = Math.min(this.bitsAvailable, size), // :uint
valu = this.word >>> (32 - bits); // :uint
if (size > 32)
logger.error('Cannot read more than 32 bits at a time');
this.bitsAvailable -= bits;
if (this.bitsAvailable > 0)
this.word <<= bits;
else if (this.bytesAvailable > 0)
this.loadWord();
bits = size - bits;
if (bits > 0 && this.bitsAvailable)
return valu << bits | this.readBits(bits);
else
return valu;
}
// ():uint
skipLZ () {
let leadingZeroCount; // :uint
for (leadingZeroCount = 0; leadingZeroCount < this.bitsAvailable; ++leadingZeroCount) {
if ((this.word & (0x80000000 >>> leadingZeroCount)) !== 0) {
// the first bit of working word is 1
this.word <<= leadingZeroCount;
this.bitsAvailable -= leadingZeroCount;
return leadingZeroCount;
}
}
// we exhausted word and still have not found a 1
this.loadWord();
return leadingZeroCount + this.skipLZ();
}
// ():void
skipUEG () {
this.skipBits(1 + this.skipLZ());
}
// ():void
skipEG () {
this.skipBits(1 + this.skipLZ());
}
// ():uint
readUEG () {
let clz = this.skipLZ(); // :uint
return this.readBits(clz + 1) - 1;
}
// ():int
readEG () {
let valu = this.readUEG(); // :int
if (0x01 & valu) {
// the number is odd if the low order bit is set
return (1 + valu) >>> 1; // add 1 to make it even, and divide by 2
} else {
return -1 * (valu >>> 1); // divide by two then make it negative
}
}
// Some convenience functions
// :Boolean
readBoolean () {
return this.readBits(1) === 1;
}
// ():int
readUByte () {
return this.readBits(8);
}
// ():int
readUShort () {
return this.readBits(16);
}
// ():int
readUInt () {
return this.readBits(32);
}
/**
* Advance the ExpGolomb decoder past a scaling list. The scaling
* list is optionally transmitted as part of a sequence parameter
* set and is not relevant to transmuxing.
* @param count {number} the number of entries in this scaling list
* @see Recommendation ITU-T H.264, Section 7.3.2.1.1.1
*/
skipScalingList (count) {
let
lastScale = 8,
nextScale = 8,
j,
deltaScale;
for (j = 0; j < count; j++) {
if (nextScale !== 0) {
deltaScale = this.readEG();
nextScale = (lastScale + deltaScale + 256) % 256;
}
lastScale = (nextScale === 0) ? lastScale : nextScale;
}
}
/**
* Read a sequence parameter set and return some interesting video
* properties. A sequence parameter set is the H264 metadata that
* describes the properties of upcoming video frames.
* @param data {Uint8Array} the bytes of a sequence parameter set
* @return {object} an object with configuration parsed from the
* sequence parameter set, including the dimensions of the
* associated video frames.
*/
readSPS () {
let
frameCropLeftOffset = 0,
frameCropRightOffset = 0,
frameCropTopOffset = 0,
frameCropBottomOffset = 0,
profileIdc, profileCompat, levelIdc,
numRefFramesInPicOrderCntCycle, picWidthInMbsMinus1,
picHeightInMapUnitsMinus1,
frameMbsOnlyFlag,
scalingListCount,
i,
readUByte = this.readUByte.bind(this),
readBits = this.readBits.bind(this),
readUEG = this.readUEG.bind(this),
readBoolean = this.readBoolean.bind(this),
skipBits = this.skipBits.bind(this),
skipEG = this.skipEG.bind(this),
skipUEG = this.skipUEG.bind(this),
skipScalingList = this.skipScalingList.bind(this);
readUByte();
profileIdc = readUByte(); // profile_idc
profileCompat = readBits(5); // constraint_set[0-4]_flag, u(5)
skipBits(3); // reserved_zero_3bits u(3),
levelIdc = readUByte(); // level_idc u(8)
skipUEG(); // seq_parameter_set_id
// some profiles have more optional data we don't need
if (profileIdc === 100 ||
profileIdc === 110 ||
profileIdc === 122 ||
profileIdc === 244 ||
profileIdc === 44 ||
profileIdc === 83 ||
profileIdc === 86 ||
profileIdc === 118 ||
profileIdc === 128) {
let chromaFormatIdc = readUEG();
if (chromaFormatIdc === 3)
skipBits(1); // separate_colour_plane_flag
skipUEG(); // bit_depth_luma_minus8
skipUEG(); // bit_depth_chroma_minus8
skipBits(1); // qpprime_y_zero_transform_bypass_flag
if (readBoolean()) { // seq_scaling_matrix_present_flag
scalingListCount = (chromaFormatIdc !== 3) ? 8 : 12;
for (i = 0; i < scalingListCount; i++) {
if (readBoolean()) { // seq_scaling_list_present_flag[ i ]
if (i < 6)
skipScalingList(16);
else
skipScalingList(64);
}
}
}
}
skipUEG(); // log2_max_frame_num_minus4
let picOrderCntType = readUEG();
if (picOrderCntType === 0) {
readUEG(); // log2_max_pic_order_cnt_lsb_minus4
} else if (picOrderCntType === 1) {
skipBits(1); // delta_pic_order_always_zero_flag
skipEG(); // offset_for_non_ref_pic
skipEG(); // offset_for_top_to_bottom_field
numRefFramesInPicOrderCntCycle = readUEG();
for (i = 0; i < numRefFramesInPicOrderCntCycle; i++)
skipEG(); // offset_for_ref_frame[ i ]
}
skipUEG(); // max_num_ref_frames
skipBits(1); // gaps_in_frame_num_value_allowed_flag
picWidthInMbsMinus1 = readUEG();
picHeightInMapUnitsMinus1 = readUEG();
frameMbsOnlyFlag = readBits(1);
if (frameMbsOnlyFlag === 0)
skipBits(1); // mb_adaptive_frame_field_flag
skipBits(1); // direct_8x8_inference_flag
if (readBoolean()) { // frame_cropping_flag
frameCropLeftOffset = readUEG();
frameCropRightOffset = readUEG();
frameCropTopOffset = readUEG();
frameCropBottomOffset = readUEG();
}
let pixelRatio = [1, 1];
if (readBoolean()) {
// vui_parameters_present_flag
if (readBoolean()) {
// aspect_ratio_info_present_flag
const aspectRatioIdc = readUByte();
switch (aspectRatioIdc) {
case 1: pixelRatio = [1, 1]; break;
case 2: pixelRatio = [12, 11]; break;
case 3: pixelRatio = [10, 11]; break;
case 4: pixelRatio = [16, 11]; break;
case 5: pixelRatio = [40, 33]; break;
case 6: pixelRatio = [24, 11]; break;
case 7: pixelRatio = [20, 11]; break;
case 8: pixelRatio = [32, 11]; break;
case 9: pixelRatio = [80, 33]; break;
case 10: pixelRatio = [18, 11]; break;
case 11: pixelRatio = [15, 11]; break;
case 12: pixelRatio = [64, 33]; break;
case 13: pixelRatio = [160, 99]; break;
case 14: pixelRatio = [4, 3]; break;
case 15: pixelRatio = [3, 2]; break;
case 16: pixelRatio = [2, 1]; break;
case 255: {
pixelRatio = [readUByte() << 8 | readUByte(), readUByte() << 8 | readUByte()];
break;
}
}
}
}
return {
width: Math.ceil((((picWidthInMbsMinus1 + 1) * 16) - frameCropLeftOffset * 2 - frameCropRightOffset * 2)),
height: ((2 - frameMbsOnlyFlag) * (picHeightInMapUnitsMinus1 + 1) * 16) - ((frameMbsOnlyFlag ? 2 : 4) * (frameCropTopOffset + frameCropBottomOffset)),
pixelRatio: pixelRatio
};
}
readSliceType () {
// skip NALu type
this.readUByte();
// discard first_mb_in_slice
this.readUEG();
// return slice_type
return this.readUEG();
}
}
export default ExpGolomb;
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