Repository: yt-dlp
Issue: [YouTube] Extract web fragment URLs for livestreams
Labels: site-enhancement,triage,site:youtube

### DO NOT REMOVE OR SKIP THE ISSUE TEMPLATE

- [X] I understand that I will be **blocked** if I *intentionally* remove or skip any mandatory\* field

### Checklist

- [X] I'm requesting a site-specific feature
- [X] I've verified that I have **updated yt-dlp to nightly or master** ([update instructions](https://github.com/yt-dlp/yt-dlp#update-channels))
- [X] I've checked that all provided URLs are playable in a browser with the same IP and same login details
- [X] I've searched [known issues](https://github.com/yt-dlp/yt-dlp/issues/3766) and the [bugtracker](https://github.com/yt-dlp/yt-dlp/issues?q=) for similar issues **including closed ones**. DO NOT post duplicates
- [X] I've read the [guidelines for opening an issue](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#opening-an-issue)
- [ ] I've read about [sharing account credentials](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#are-you-willing-to-share-account-details-if-needed) and I'm willing to share it if required

### Region

_No response_

### Example URLs

https://youtu.be/jfKfPfyJRdk

### Provide a description that is worded well enough to be understood

I want to use yt-dlp to extract web dash fragment urls for YouTube livestreams. Right now yt-dlp only extracts fragment URLs from the dash manifest. The web player, on the other hand, extracts them from `adaptiveFormats` in the html (and fixes nsig). I can get the fragment URLs from the dash manifest with `yt-dlp  --extractor-args 'youtube:player_client=web;formats=incomplete,duplicate' --print fragment_base_url -f 248-dash jfKfPfyJRdk` resulting in: 
```
https://rr3---sn-4o.googlevideo.com/videoplayback/expire/1717329791/ei/HwtcZuHMO6qLkucPhMOgyAQ/ip/73.212.163.75/id/jfKfPfyJRdk.2/itag/248/source/yt_live_broadcast/requiressl/yes/xpc/EgVo2aDSNQ%3D%3D/spc/UWF9fyE83WjFMibaoKWv_Jiwsw_G_Dt7xaQZg8zWIHSx1am0NgqeT9bd-nEm/vprv/1/playlist_type/DVR/ratebypass/yes/mime/video%2Fwebm/live/1/gir/yes/noclen/1/dur/5.000/rqh/1/keepalive/yes/sparams/expire,ei,ip,id,itag,source,requiressl,xpc,spc,vprv,playlist_type,ratebypass,mime,live,gir,noclen,dur,rqh/sig/AJfQdSswRQIhAPn5UhHoA5R-wlo3HjAxdUdImcD7e6DmzlIp5uRYlgUQAiBMOSz3tcD1vSZq5eEwAv0DEFmzeZ1gL1R__cgqyMzLdQ%3D%3D/initcwndbps/1875000/mh/rr/mm/44/mn/sn-4o/ms/lva/mt/1717307776/mv/m/mvi/3/pl/15/lsparams/initcwndbps,mh,mm,mn,ms,mv,mvi,pl/lsig/AHlkHjAwRQIhAINV2QJmCBRY7gX6Qd7zs_RUu_q9gMzKDGlSVGk6_ZccAiB8PxaBWEMF3g8GlL6iyIsDOkfTaW0l6LNebnWYpEcfJg%3D%3D/
```
However the fragment URLs used by the web player are different and cannot be converted:
```
https://rr4---sn-nx57ynsl.googlevideo.com/videoplayback?expire=1716898457&ei=OXZVZqvQEcTAsfIP4LW5oAk&ip=156.146.51.133&id=jfKfPfyJRdk.2&itag=248&aitags=242,243,244,247,248,278&source=yt_live_broadcast&requiressl=yes&xpc=EgVo2aDSNQ%3D%3D&hcs=ir,sd&mh=rr&mm=44,26&mn=sn-nx57ynsl,sn-a5meknds&ms=lva,onr&mv=m&mvi=4&pl=24&smhost=,rr3---sn-a5mekn6d.googlevideo.com&initcwndbps=998750&bui=AWRWj2Q1l1aXjLOowdDZq1uar_Suo6ENVmWnppLwt1A8hZBSoGDfiXHnDbI2f_yrbm_I3alif10vHJar&spc=UWF9f3jKiv5XfNEQMVPKzz2tBIdAvsl0CLg9xCX6Pxfd67fpFyQgHhGLWU9q&vprv=1&live=1&hang=1&noclen=1&svpuc=1&mime=video%2Fwebm&ns=FIiOz8Fab-jivO1lXcvGLPYQ&rqh=1&gir=yes&mt=1716876509&fvip=3&keepalive=yes&c=WEB&sefc=1&n=xcbcLceweULNjhjLl&sparams=expire,ei,ip,id,aitags,source,requiressl,xpc,bui,spc,vprv,live,hang,noclen,svpuc,mime,ns,rqh,gir&sig=AJfQdSswRQIhAO1V0td1NFiMFCdxJLpheT4iIxFmroRsgLxYBq-jXnH-AiBZ9A31wfJjbwkq2ueih25pbpoicAHYz4SdBCEEKHj2Ng%3D%3D&lsparams=hcs,mh,mm,mn,ms,mv,mvi,pl,smhost,initcwndbps&lsig=AHWaYeowRAIgZ-Mm8_dEHfg63wnXcye4x83DoctYebY7huXPGMIiK2YCIH2i163BA81u8NR5YuwdxKrJL8GWThM1Ce98hpNxsT0l
```
To be clear, these always point to the same data (as far as I know), but the web URLs are preferable in some circumstances. For example, with this URL one can simply replace `itag` with anything from `aitags` to change the format. I mainly just want these extracted to pass to other applications. I don't care if yt-dlp makes them downloadable natively (which is certainly possible but likely not worth the effort).

yt-dlp could do this already but there is a check on lines 3826-3827 of `youtube.py`  which explicitly prevents it.
```
if fmt.get('targetDurationSec'):
 continue

itag = str_or_none(fmt.get('itag')) 
...
```
If I remove the check then `yt-dlp jfKfPfyJRdk -f 248 --extractor-args 'youtube:player_client=web;formats=incomplete,duplicate' --print url` gives the desired URL. Of course, if one tries to download this format it will fail since yt-dlp treats it as https.

Would it be possible to add an argument to bypass this check? Perhaps something like `formats=broken` so people don't accidentally use it. If this is undesirable, saving the web URLs to a separate metadata field (something like `fragment_base_web_url`) in the regular dash formats would be just as good but would not be quite as straightforward to implement.

### Provide verbose output that clearly demonstrates the problem

- [X] Run **your** yt-dlp command with **-vU** flag added (`yt-dlp -vU <your command line>`)
- [ ] If using API, add `'verbose': True` to `YoutubeDL` params instead
- [X] Copy the WHOLE output (starting with `[debug] Command-line config`) and insert it below

### Complete Verbose Output

```shell
> yt-dlp -vU --extractor-args 'youtube:player_client=web;formats=incomplete,duplicate' --print url -f 248 jfKfPfyJRdk
[debug] Command-line config: ['-vU', '--extractor-args', 'youtube:player_client=web;formats=incomplete,duplicate', '--print', 'url', '-f', '248', 'jfKfPfyJRdk']
[debug] Encodings: locale cp1252, fs utf-8, pref cp1252, out utf-8, error utf-8, screen utf-8
[debug] yt-dlp version nightly@2024.06.01.232725 from yt-dlp/yt-dlp-nightly-builds [db50f19d7] (win_exe)
[debug] Python 3.8.10 (CPython AMD64 64bit) - Windows-10-10.0.19045-SP0 (OpenSSL 1.1.1k  25 Mar 2021)
[debug] exe versions: ffmpeg git-2020-07-29-cbb6ba2, ffprobe git-2020-07-29-cbb6ba2, phantomjs 2.1.1
[debug] Optional libraries: Cryptodome-3.20.0, brotli-1.1.0, certifi-2024.02.02, curl_cffi-0.5.10, mutagen-1.47.0, requests-2.32.3, sqlite3-3.35.5, urllib3-2.2.1, websockets-12.0
[debug] Proxy map: {}
[debug] Request Handlers: urllib, requests, websockets, curl_cffi
[debug] Loaded 1820 extractors
[debug] Fetching release info: https://api.github.com/repos/yt-dlp/yt-dlp-nightly-builds/releases/latest
Latest version: nightly@2024.06.01.232725 from yt-dlp/yt-dlp-nightly-builds
yt-dlp is up to date (nightly@2024.06.01.232725 from yt-dlp/yt-dlp-nightly-builds)
[youtube] Extracting URL: jfKfPfyJRdk
[youtube] jfKfPfyJRdk: Downloading webpage
[youtube] jfKfPfyJRdk: Downloading m3u8 information
[youtube] jfKfPfyJRdk: Downloading MPD manifest
[debug] Sort order given by extractor: quality, res, fps, hdr:12, source, vcodec:vp9.2, channels, acodec, lang, proto
[debug] Formats sorted by: hasvid, ie_pref, quality, res, fps, hdr:12(7), source, vcodec:vp9.2(10), channels, acodec, lang, proto, size, br, asr, vext, aext, hasaud, id
ERROR: [youtube] jfKfPfyJRdk: Requested format is not available. Use --list-formats for a list of available formats
Traceback (most recent call last):
  File "yt_dlp\YoutubeDL.py", line 1606, in wrapper
  File "yt_dlp\YoutubeDL.py", line 1762, in __extract_info
  File "yt_dlp\YoutubeDL.py", line 1821, in process_ie_result
  File "yt_dlp\YoutubeDL.py", line 2955, in process_video_result
yt_dlp.utils.ExtractorError: [youtube] jfKfPfyJRdk: Requested format is not available. Use --list-formats for a list of available formats
```