Workaround: new regex pattern to find JS player signature function

[Khang-NT]

Before submitting a pull request make sure you have:

• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
• Searched the bugtracker for similar pull requests
• Checked the code with flake8

In order to be accepted and merged into youtube-dl each piece of code must be in public domain or released under Unlicense. Check one of the following options:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

---

Description of your pull request and other information

Fix #17457
Idea: The signature decrypt function body always start with a command like this a=a.split("");, I use this to find the entry.
https://regex101.com/r/L7kWtA/1

[phyllisstein]

FWIW I can confirm this fix works with a problem video:

Log output

~/Downloads ❯❯❯ ydl --verbose 'https://www.youtube.com/watch?v=WgQHQ-KeUaw'
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'--recode-video', u'mp4', u'--verbose', u'https://www.youtube.com/watch?v=WgQHQ-KeUaw']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2018.09.01
[debug] Python version 2.7.15 (CPython) - Darwin-18.0.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.0.2, ffprobe 4.0.2, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] WgQHQ-KeUaw: Downloading webpage
[youtube] WgQHQ-KeUaw: Downloading video info webpage
[youtube] {43} signature length 41.42, html5 player vflvABTsY
[youtube] WgQHQ-KeUaw: Downloading player https://www.youtube.com/yts/jsbin/player-vflvABTsY/en_US/base.js
[youtube] {18} signature length 41.42, html5 player vflvABTsY
[youtube] {36} signature length 41.42, html5 player vflvABTsY
[youtube] {17} signature length 41.42, html5 player vflvABTsY
[youtube] {135} signature length 41.42, html5 player vflvABTsY
[youtube] {244} signature length 41.42, html5 player vflvABTsY
[youtube] {134} signature length 41.42, html5 player vflvABTsY
[youtube] {243} signature length 41.42, html5 player vflvABTsY
[youtube] {133} signature length 41.42, html5 player vflvABTsY
[youtube] {242} signature length 41.42, html5 player vflvABTsY
[youtube] {160} signature length 41.42, html5 player vflvABTsY
[youtube] {278} signature length 41.42, html5 player vflvABTsY
[youtube] {140} signature length 41.42, html5 player vflvABTsY
[youtube] {171} signature length 41.42, html5 player vflvABTsY
[youtube] {249} signature length 41.42, html5 player vflvABTsY
[youtube] {250} signature length 41.42, html5 player vflvABTsY
[youtube] {251} signature length 41.42, html5 player vflvABTsY
[debug] Default format spec: bestvideo+bestaudio/best
WARNING: Requested formats are incompatible for merge and will be merged into mkv.
[debug] Invoking downloader on u'https://r2---sn-ab5l6ndy.googlevideo.com/videoplayback?dur=1765.360&id=o-AIH-Ev8OcVFwB3IHIr43p9xWcrp2IP0dNUrPsBy6vRvE&initcwndbps=1242500&ei=jcWSW93pJo-N8wT2prnACQ&c=WEB&gir=yes&requiressl=yes&sparams=aitags%2Cclen%2Cdur%2Cei%2Cgir%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Crequiressl%2Csource%2Cexpire&ms=au%2Conr&ipbits=0&pl=32&mv=m&mt=1536345348&aitags=133%2C134%2C135%2C160%2C242%2C243%2C244%2C278&mm=31%2C26&keepalive=yes&key=yt6&ip=2604%3A2000%3A12c0%3A6de%3Af487%3A4565%3Aa374%3A53&clen=91672120&mn=sn-ab5l6ndy%2Csn-vgqskn7l&source=youtube&fvip=6&lmt=1536344003156412&expire=1536367085&itag=135&mime=video%2Fmp4&signature=39B29CC2B59C43EDE4236CF1D7E4AD9D03B1620D.C993F726A361993E2DA44F31DB95A996E23FB4D1&ratebypass=yes'
[download] Destination: Liza & David (Unaired Pilot)-WgQHQ-KeUaw.f135.mp4
[download] 100% of 87.43MiB in 00:17
[debug] Invoking downloader on u'https://r2---sn-ab5l6ndy.googlevideo.com/videoplayback?dur=1765.941&id=o-AIH-Ev8OcVFwB3IHIr43p9xWcrp2IP0dNUrPsBy6vRvE&initcwndbps=1242500&ei=jcWSW93pJo-N8wT2prnACQ&c=WEB&gir=yes&requiressl=yes&sparams=clen%2Cdur%2Cei%2Cgir%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Crequiressl%2Csource%2Cexpire&ms=au%2Conr&ipbits=0&pl=32&mv=m&mt=1536345348&mn=sn-ab5l6ndy%2Csn-vgqskn7l&mm=31%2C26&keepalive=yes&key=yt6&ip=2604%3A2000%3A12c0%3A6de%3Af487%3A4565%3Aa374%3A53&clen=28420218&source=youtube&fvip=6&lmt=1493885804061473&expire=1536367085&itag=251&mime=audio%2Fwebm&signature=2C522DE6484E2A2AEEC193FAE11A805AF2734A32.983B55E7A9220095F4E36ADEC1EFCDDC4F229B4D&ratebypass=yes'
[download] Destination: Liza & David (Unaired Pilot)-WgQHQ-KeUaw.f251.webm
[download] 100% of 27.10MiB in 00:04

[cyberboysumanjay]

I can confirm this working. Merge it asap and release an update. Cheers!

[Bleuzen]

YouTube seemed to change it back. I'm still using the 2018.09.01 version (because this is the one which is currently in my distribution repository)
and since today I can download videos again. All videos so far. And youtube-dl --version outputs:
2018.09.01
The same version that didn't work yesterday.