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MP3 Extractor added

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n1073645 2020-03-23 10:10:47 +00:00
parent b69e4567c0
commit 090bf3f8ec
1 changed files with 27 additions and 0 deletions
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27
src/core/lib/FileSignatures.mjs
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@ -3077,10 +3077,12 @@ export function extractWAV(bytes, offset) {
export function extractMP3(bytes, offset) {
const stream = new Stream(bytes.slice(offset));
// Constants for flag byte.
const bitRateIndexes = ["free", 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 160000, 192000, 224000, 256000, 320000, "bad"];
const samplingRateFrequencyIndex = [44100, 48000, 32000, "reserved"];
// ID3 tag, move over it.
if ((stream.getBytes(3).toString() === [0x49, 0x44, 0x33].toString())) {
stream.moveTo(6);
const tagSize = (stream.readInt(1) << 21) | (stream.readInt(1) << 14) | (stream.readInt(1) << 7) | stream.readInt(1);
@ -3088,20 +3090,45 @@ export function extractMP3(bytes, offset) {
} else {
stream.moveTo(0);
}
// Loop over all the frame headers in the file.
while (stream.hasMore()) {
// If it has an old TAG frame at the end of it, fixed size, 128 bytes.
if (stream.getBytes(3) === [0x54, 0x41, 0x47].toString()) {
stream.moveForwardsBy(125);
break;
}
// If not start of frame.
if (stream.getBytes(2).toString() !== [0xff, 0xfb].toString()) {
stream.moveBackwardsBy(2);
break;
}
// Read flag byte.
const flags = stream.readInt(1);
// Extract frame bitrate from flag byte.
const bitRate = bitRateIndexes[flags >> 4];
// Extract frame samplerate from flag byte.
const sampleRate = samplingRateFrequencyIndex[(flags & 0x0f) >> 2];
// Padding if the frame size is not a multiple of the bitrate.
const padding = (flags & 0x02) >> 1;
// Things that are either not standard or undocumented.
if (bitRate === "free" || bitRate === "bad" || sampleRate === "reserved") {
stream.moveBackwardsBy(1);
break;
}
// Formula: FrameLength = (144 * BitRate / SampleRate ) + Padding
const frameSize = Math.floor(((144 * bitRate) / sampleRate) + padding);
// If the next move goes past the end of the bytestream then extract the entire bytestream.
// We assume complete frames in the above formula because there is no field that suggests otherwise.
if ((stream.position + frameSize) > stream.length) {
stream.moveTo(stream.length);
break;