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cut: initial prototype
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dumbmoron
parent
335696686c
commit
7f563ef485
@ -33,6 +33,7 @@
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"express": "^4.18.1",
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"express-rate-limit": "^6.3.0",
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"ffmpeg-static": "^5.1.0",
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"ffprobe-static": "^3.1.0",
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"hls-parser": "^0.10.7",
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"ipaddr.js": "2.1.0",
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"nanoid": "^4.0.2",
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270
src/modules/stream/cut.js
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270
src/modules/stream/cut.js
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@ -0,0 +1,270 @@
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import { strict as assert } from 'node:assert';
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import { spawn } from 'node:child_process';
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import { path as ffprobe } from 'ffprobe-static';
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function mapFormat(format) {
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if (format?.includes('webm'))
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return 'webm';
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if (format?.includes('mp4'))
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return 'mp4';
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throw new Error(`unknown format: ${format}`);
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}
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const close_enough = (a, b) => Math.abs(a - b) < 0.02;
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const last = arr => arr[arr.length - 1];
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const output = process => last(process.stdio);
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const lerp = (a, b, α) => Number(a) + α * (b - a);
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function getKeyframesAround(url, { start, end }) {
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start = Math.floor(start), end = Math.ceil(end);
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assert(end > start);
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const ε = 30;
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return new Promise((resolve, reject) => {
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let process;
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try {
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process = spawn(ffprobe, [
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'-loglevel', '-8',
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'-of', 'json',
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'-skip_frame', 'nokey',
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'-show_entries', [
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'stream=duration,codec_name,bit_rate',
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'format=bit_rate,format_name',
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'frame=pts_time'
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].join(':'),
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'-select_streams', 'v:0',
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'-read_intervals', Object.values({
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startInterval: `${start}%+${ε}`,
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endInterval: `${end - ε}%+${ε * 2}`
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}).join(','),
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url
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]);
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const bufs = [];
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process.stdout.on('data', buf => bufs.push(buf))
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process.on('exit', (code) => {
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if (code !== 0) {
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return reject('non-zero/unexpected return value');
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}
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const data = JSON.parse(Buffer.concat(bufs));
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if (!data?.streams?.[0]?.duration) {
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return reject('could not get video duration');
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}
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if (Number(data?.streams[0]?.duration) < Number(end)) {
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return reject(
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'cut out of bounds: ' +
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`(duration ${data?.streams[0]?.duration} < end ${start})`
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)
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}
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const stream = data.streams[0];
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const out = {
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keyframes: data.frames.map(f => f.pts_time),
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codec: stream?.codec_name,
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format: mapFormat(data.format?.format_name),
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bitrate: data?.format?.bit_rate
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};
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if (!out.codec || !out.bitrate || !out.format) {
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return reject('could not get stream info');
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}
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return resolve(out);
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});
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process.on('error', reject);
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process.stdout.on('error', reject);
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} catch {
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process.kill('SIGKILL');
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}
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})
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}
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async function getBoundingKeyframes(url, { start, end }) {
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const { keyframes, ...info } = await getKeyframesAround(url, { start, end });
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const afterStart = keyframes.find(k => Number(k) >= Number(start)),
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beforeEnd = keyframes.findLast(k => Number(k) <= Number(end));
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const afterStartNext = keyframes[keyframes.indexOf(afterStart) + 1];
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const beforeEndNext = keyframes[keyframes.indexOf(beforeEnd) + 1];
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if (!afterStartNext || !beforeEndNext)
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throw 'not enough keyframes'
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return {
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afterStart, beforeEnd,
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cleanCut: {
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start: close_enough(afterStart, start),
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end: close_enough(beforeEnd, end)
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},
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shifted: {
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/* we need to provide a timestamp that is little bit after the actual keyframe
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* this is due to the fact that ffmpeg's lossless cut actually cuts on the
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* "previous" keyframe, so if we supply the exact keyframe timestamp, it won't
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* line up and the start/end transcodes will not sync up with it */
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afterStart: lerp(afterStart, afterStartNext, 0.2),
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beforeEnd: lerp(beforeEnd, beforeEndNext, 0.2),
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},
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...info
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};
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}
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function spawnStream(args, inputs = 0) {
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return spawn(
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'ffmpeg',
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[ '-loglevel', '-8', ...args, 'pipe:' + (inputs + 3) ],
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{
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stdio: [
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'inherit', 'inherit', 'inherit',
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...Array(inputs).fill('pipe'),
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'pipe'
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]
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}
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)
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}
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function makeStream(...args) {
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const process = spawnStream(...args);
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output(process).process = process;
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return output(process);
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}
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function transcode(url, from, to, { bitrate, format, codec, filter }) {
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return makeStream([
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'-ss', from,
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'-i', url,
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'-copyts',
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'-to', to,
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...(filter ? ['-filter:v', filter] : []),
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'-an',
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'-b:v', (bitrate * 1.2).toFixed(6),
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'-f', format,
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'-movflags', 'frag_keyframe+empty_moov',
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'-vcodec', codec
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]);
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}
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function cut(type, url, from, to, info) {
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let toggles;
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switch (type) {
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case 'audio':
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toggles = ['-vn'];
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break;
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case 'video':
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toggles = [ '-c:v', 'copy', '-an' ];
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from = info.shifted.afterStart;
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to = info.shifted.beforeEnd;
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break;
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default:
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throw `invalid cut type: ${type}`;
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}
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return makeStream([
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'-ss', from,
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'-i', url,
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'-copyts',
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'-to', to,
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'-f', info.format,
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'-movflags', 'frag_keyframe+empty_moov',
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...toggles
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]);
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}
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function mergeVideoOnly(streams, info) {
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let fd = 3;
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const input = streams.map(
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() => `file 'pipe:${++fd}'`
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).join('\n')
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const args = [
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'-f', 'concat',
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'-safe', '0',
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'-protocol_whitelist', 'file,pipe',
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'-i', 'pipe:3',
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'-c', 'copy',
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'-movflags', 'frag_keyframe+empty_moov',
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'-f', info.format
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];
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const process = spawnStream(args, fd - 2);
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process.stdio[3].write(input);
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process.stdio[3].end();
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return process;
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}
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function mergeAudioVideo(info) {
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return spawnStream([
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'-i', 'pipe:3',
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'-i', 'pipe:4',
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'-movflags', 'frag_keyframe+empty_moov',
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'-f', info.format,
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'-c', 'copy',
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], 2);
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}
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export async function makeCut(url, { start, end }, audio) {
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let processes = [];
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try {
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const {
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afterStart, beforeEnd,
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cleanCut, ...info
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} = await getBoundingKeyframes(url, { start, end });
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let streams = [];
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if (!cleanCut.start) {
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streams.push(
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transcode(url, start, afterStart, {
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filter: `select=not(eq(t\\,${afterStart}))`,
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...info
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})
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)
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}
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streams.push(cut('video', url, afterStart, beforeEnd, info))
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if (!cleanCut.end) {
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streams.push(
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transcode(url, beforeEnd, end, {
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filter: 'select=not(eq(n\\,0))',
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...info
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})
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)
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}
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processes.push(...streams.map(s => s.process));
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if (audio) {
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audio = cut('audio', audio, start, end, info);
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processes.push(audio.process);
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}
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const videoMerge = mergeVideoOnly(streams, info);
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processes.push(videoMerge);
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for (let fd = 0; fd < streams.length; ++fd) {
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streams[fd].pipe(videoMerge.stdio[4 + fd]);
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}
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let finalMerge = videoMerge;
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if (audio) {
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finalMerge = mergeAudioVideo(info);
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const [,,, audioIn, videoIn] = finalMerge.stdio;
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output(videoMerge).pipe(videoIn);
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audio.pipe(audioIn);
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}
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return output(finalMerge);
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} catch {
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for (const process of processes)
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process.kill('SIGKILL');
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}
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}
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