yt-dlp error: Falling back to generic n function search...

[Mihara]

I've been using the prebuilt executabl on Linux, and recently, my logs are full of

[ytdl-sub:yt-dlp] [youtube] Extracting URL: https://www.youtube.com/shorts/6ziGAbDJQdY
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] 6ziGAbDJQdY: Downloading webpage
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] 6ziGAbDJQdY: Downloading android sdkless player API JSON
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] 6ziGAbDJQdY: Downloading tv client config
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] 6ziGAbDJQdY: Downloading tv player API JSON
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] 6ziGAbDJQdY: Downloading web safari player API JSON
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] 6ziGAbDJQdY: Downloading player 6e4dbefe-main
[ytdl-sub:yt-dlp] WARNING: [youtube] Falling back to generic n function search
          player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
[ytdl-sub:yt-dlp] WARNING: [youtube] 6ziGAbDJQdY: nsig extraction failed: Some formats may be missing
          n = K9IcHlc6w2ej4Itb ; player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
          Please report this issue on  https://github.com/yt-dlp/yt-dlp/issues?q= , filling out the appropriate issue

Nothing gets downloaded out of my ~60 subscriptions, even though it's been working fine for quite a while.

ytdl-sub is automatically updated to the latest version every day, half an hour before the subscription download starts:

update-youtube-downloaders[3011782]: Latest version: stable@2025.10.22 from yt-dlp/yt-dlp
update-youtube-downloaders[3011782]: yt-dlp is up to date (stable@2025.10.22 from yt-dlp/yt-dlp)
update-youtube-downloaders[3011781]: ytdl-sub is 2025.10.23, latest is 2025.10.23, nothing to update.

#!/bin/bash

# yt-dlp is easy.
/usr/local/bin/yt-dlp -U

# ytdl-sub doesn't self-update so a more complex dance is needed.
VERSION=$(ytdl-sub -v | cut -d "+" -f 1 | cut -d " " -f 2)
UPSTREAM=$(curl -sL https://api.github.com/repos/jmbannon/ytdl-sub/releases/latest | jq -r ".tag_name")

if [ "$VERSION" != "$UPSTREAM" ]; then
        curl -s -L -o /usr/local/bin/ytdl-sub https://github.com/jmbannon/ytdl-sub/releases/latest/download/ytdl-sub
        chmod +x /usr/local/bin/ytdl-sub
else
        echo ytdl-sub is $VERSION, latest is $UPSTREAM, nothing to update.
fi

Just in case it is not bundled inside the single-executable, deno is installed on the system:

deno --version
deno 2.5.4 (stable, release, x86_64-unknown-linux-gnu)
v8 14.0.365.5-rusty
typescript 5.9.2

Regular yt-dlp also stumbles into this error, however, it doesn't stop there and goes on to actually download as requested:

[youtube] Extracting URL: https://www.youtube.com/watch?v=UJRQA-Ej6UI
[youtube] UJRQA-Ej6UI: Downloading webpage
[youtube] UJRQA-Ej6UI: Downloading android sdkless player API JSON
[youtube] UJRQA-Ej6UI: Downloading tv client config
[youtube] UJRQA-Ej6UI: Downloading tv player API JSON
[youtube] UJRQA-Ej6UI: Downloading web safari player API JSON
[youtube] UJRQA-Ej6UI: Downloading player 6e4dbefe-main
WARNING: [youtube] Falling back to generic n function search
         player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
WARNING: [youtube] UJRQA-Ej6UI: nsig extraction failed: Some formats may be missing
         n = lqDKIjMnrJMlYYGh ; player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
         Please report this issue on  https://github.com/yt-dlp/yt-dlp/issues?q= , filling out the appropriate issue template. Confirm you are on the latest version using  yt-dlp -U
WARNING: [youtube] UJRQA-Ej6UI: Some web_safari client https formats have been skipped as they are missing a url. YouTube is forcing SABR streaming for this client. See  https://github.com/yt-dlp/yt-dlp/issues/12482  for more details
WARNING: [youtube] UJRQA-Ej6UI: Some web client https formats have been skipped as they are missing a url. YouTube is forcing SABR streaming for this client. See  https://github.com/yt-dlp/yt-dlp/issues/12482  for more details
[youtube] UJRQA-Ej6UI: Downloading m3u8 information
[info] UJRQA-Ej6UI: Downloading subtitles: de, pt, es, live_chat
[info] UJRQA-Ej6UI: Downloading 1 format(s): 251
...

[jmbannon]

Hmm, hopefully this isnt executable specific. Could you try running the pip version of ytdl-sub to see if that works?

[Mihara]

It does not, the symptoms are identical:

$ pip list
Package            Version
------------------ ----------
Brotli             1.1.0
certifi            2025.10.5
charset-normalizer 3.4.4
colorama           0.4.6
filetype           1.2.0
idna               3.11
mediafile          0.13.0
mergedeep          1.3.4
mutagen            1.47.0
pip                24.0
pycryptodomex      3.23.0
PyYAML             6.0.3
requests           2.32.5
urllib3            2.5.0
websockets         15.0.1
yt-dlp             2025.10.22
ytdl-sub           2025.10.23

$ which ytdl-sub
/home/user/experiment/.direnv/python-3.12.3/bin/ytdl-sub

#!/bin/bash

CFG="/home/user/experiment"
TGT="/mnt/array/main/Jellyfin/YouTube"

# Set the umask so that files are created in a way
# that jellyfin can later delete, and run it with nice so it doesn't
# steal cpu from transcoding.
(umask 0002 && nice ytdl-sub -c $CFG/config.yaml sub $CFG/channels.yaml)

[ytdl-sub] Validating subscriptions...
[ytdl-sub] Beginning subscription download for The Critical Drinker
[ytdl-sub:preset] Throttle protection is enabled. Disable using the override variable `enable_throttle_protection: False`
[ytdl-sub:yt-dlp] [youtube:tab] Extracting URL: https://www.youtube.com/@TheCriticalDrinker
[ytdl-sub:yt-dlp] [youtube:tab] @TheCriticalDrinker: Downloading webpage
[ytdl-sub:yt-dlp] [youtube:tab] Downloading all uploads of the channel. To download only the videos in a specific tab, pass the tab's URL
[ytdl-sub:yt-dlp] [youtube:tab] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube:tab] @TheCriticalDrinker/streams: Downloading webpage
[ytdl-sub:yt-dlp] [youtube:tab] Downloading as multiple playlists, separated by tabs. To download as a single playlist instead, pass https://www.youtube.com/playlist?list=UUS
JPFQdZwrOutnmSFYtbstA
[ytdl-sub:yt-dlp] [download] Downloading playlist: The Critical Drinker
[ytdl-sub:yt-dlp] [info] Writing playlist metadata as JSON to: /mnt/array/main/Jellyfin/YouTube/.ytdl-sub/The Critical Drinker/@TheCriticalDrinker.info.json
[ytdl-sub:yt-dlp] [youtube:tab] Playlist The Critical Drinker: Downloading 2 items of 2
[ytdl-sub:yt-dlp] [download] Downloading item 1 of 2
[ytdl-sub:yt-dlp] [download] Downloading playlist: The Critical Drinker - Live
[ytdl-sub:yt-dlp] [info] Writing playlist metadata as JSON to: /mnt/array/main/Jellyfin/YouTube/.ytdl-sub/The Critical Drinker/UCSJPFQdZwrOutnmSFYtbstA.info.json
[ytdl-sub:yt-dlp] [youtube:tab] Playlist The Critical Drinker - Live: Downloading 11 items of 11
[ytdl-sub:yt-dlp] [download] Downloading item 1 of 11
[ytdl-sub:yt-dlp] [youtube] Extracting URL: https://www.youtube.com/watch?v=l4WDQ-NGjZI
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:downloader] Downloading metadata for The Critical Drinker
[ytdl-sub:downloader] Downloading metadata for The Critical Drinker - Live
[ytdl-sub:yt-dlp] [youtube] l4WDQ-NGjZI: Downloading webpage
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] l4WDQ-NGjZI: Downloading android sdkless player API JSON
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] l4WDQ-NGjZI: Downloading tv client config
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] l4WDQ-NGjZI: Downloading tv player API JSON
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] l4WDQ-NGjZI: Downloading web safari player API JSON
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] l4WDQ-NGjZI: Downloading player 6e4dbefe-main
[ytdl-sub:yt-dlp] WARNING: [youtube] Falling back to generic n function search
         player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
[ytdl-sub:yt-dlp] WARNING: [youtube] l4WDQ-NGjZI: nsig extraction failed: Some formats may be missing
         n = NEFj5I_J25DV2ZX6 ; player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
         Please report this issue on  https://github.com/yt-dlp/yt-dlp/issues?q= , filling out the appropriate issue template. Confirm you are on the latest version using  yt
-dlp -U
[ytdl-sub:yt-dlp] WARNING: [youtube] l4WDQ-NGjZI: Some web_safari client https formats have been skipped as they are missing a url. YouTube is forcing SABR streaming for this
 client. See  https://github.com/yt-dlp/yt-dlp/issues/12482  for more details
[ytdl-sub:yt-dlp] WARNING: [youtube] l4WDQ-NGjZI: Some web client https formats have been skipped as they are missing a url. YouTube is forcing SABR streaming for this client
. See  https://github.com/yt-dlp/yt-dlp/issues/12482  for more details
[ytdl-sub:yt-dlp] [youtube] Sleeping 0.75 seconds ...
[ytdl-sub:yt-dlp] [youtube] l4WDQ-NGjZI: Downloading m3u8 information
[ytdl-sub:yt-dlp] [download] The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) does not pass filter (upload_date >= 20251006), skipping ..
[ytdl-sub:downloader] Beginning downloads for https://www.youtube.com/@TheCriticalDrinker
[ytdl-sub:throttle-protection] Sleeping between subscriptions for 14.06 seconds
[ytdl-sub]
No files changed for The Critical Drinker
[ytdl-sub] Download Summary:
The Critical Drinker     0 0 0     3 ✔
Total: 1                 0 0 0     3 Success

My config is fairly extensive, but at a glance only option that could be even remotely relevant is the proxy address (tubes are restricted here) and that is exactly the same as what's written into the yt-dlp config. (or it wouldn't even be able to download the html)

There's the format: "(bv*[height<=1080]+bestaudio/best[height<=1080])", but that shouldn't just make it fail to download anything, right?

$ yt-dlp l4WDQ-NGjZI
[youtube] Extracting URL: l4WDQ-NGjZI
[youtube] l4WDQ-NGjZI: Downloading webpage
[youtube] l4WDQ-NGjZI: Downloading android sdkless player API JSON
[youtube] l4WDQ-NGjZI: Downloading tv client config
[youtube] l4WDQ-NGjZI: Downloading tv player API JSON
[youtube] l4WDQ-NGjZI: Downloading web safari player API JSON
[youtube] l4WDQ-NGjZI: Downloading player 6e4dbefe-main
WARNING: [youtube] Falling back to generic n function search
         player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
WARNING: [youtube] l4WDQ-NGjZI: nsig extraction failed: Some formats may be missing
         n = v8x04_kKKaX1KL5V ; player = https://www.youtube.com/s/player/6e4dbefe/player_ias.vflset/en_US/base.js
         Please report this issue on  https://github.com/yt-dlp/yt-dlp/issues?q= , filling out the appropriate issue template. Confirm you are on the latest version using  yt-dlp -U
WARNING: [youtube] l4WDQ-NGjZI: Some web_safari client https formats have been skipped as they are missing a url. YouTube is forcing SABR streaming for this client. See  https://github.com/yt-dlp/yt-dlp/issues/12482  for more details
WARNING: [youtube] l4WDQ-NGjZI: Some web client https formats have been skipped as they are missing a url. YouTube is forcing SABR streaming for this client. See  https://github.com/yt-dlp/yt-dlp/issues/12482  for more details
[youtube] l4WDQ-NGjZI: Downloading m3u8 information
[info] l4WDQ-NGjZI: Downloading subtitles: live_chat
[info] l4WDQ-NGjZI: Downloading 1 format(s): 136+251
[info] Writing video description to: The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].description
[info] Writing video subtitles to: The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].live_chat.json
[youtube_live_chat] Downloading live chat
[youtube_live_chat] Total fragments: unknown (live)
[download] Destination: The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].live_chat.json
[download] 100% of    5.18MiB in 00:00:18 at 283.56KiB/s
[info] Writing video metadata as JSON to: The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].info.json
[download] Destination: The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].f136.mp4
[download] 100% of   22.51MiB in 00:00:06 at 3.57MiB/s
[download] Destination: The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].f251.webm
[download] 100% of  104.03MiB in 00:00:18 at 5.52MiB/s
[Merger] Merging formats into "The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].mkv"
Deleting original file The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].f136.mp4 (pass -k to keep)
Deleting original file The Drinker's Unhappy Hour - Episode 1 (feat. Bowlestrek) [l4WDQ-NGjZI].f251.webm (pass -k to keep)
WARNING: JSON subtitles cannot be embedded

(I didn't even know that yt-dlp can recognize YouTube IDs on sight, nice.)

[jmbannon]

maybe you need an env variable when running to point ytdlp to your deno install. My recommendation is take a look at ytdlp GH issues to see if someone has a fix

[Mihara]

Well, if I'm reading their issues correctly, the published yt-dlp doesn't even actually use deno yet, never mind bundle it. That's for the next release though.

Meanwhile, upon reading deeper into the logs, though, it seems to me that the actual problem might be something different: Notice how ytdl-sub gives up when saying that the video does not pass the 3-week filter.

Somehow, ytdl-sub keeps trying to download and rejecting 3-8 year old videos, with no obvious rhyme nor reason for picking those particular ones. Well, they really don't pass filters.

I did not look into ytdl-sub code to investigate how does it determine which videos to download, so - could I have fallen victim to an A/B test that your parser simply didn't anticipate?

[jmbannon]

No the only a/b tests are from YouTube. Need to see your config and subscription setup to debug the filter issue

[Mihara]

Sorry for not getting back to this earlier, we had a censorship meltdown for a few days. Anyway...

No the only a/b tests are from YouTube.

This is what I meant though? My theory was that something changed on youtube side just for me and ytdl-sub can no longer parse channel videos properly.

In any case, I think I identified the actual cause:

    youtube_show:
        preset:
            - "useproxy"
            - "Jellyfin TV Show by Date"
            #- "Chunk Downloads"
            - "Filter Keywords"
            - "Only Recent"
            - "sponsorblock"
            - "selfcontained"
            - "humanize"
            - "max_1080p_mkv"

If I enable "Chunk Downloads", as I had it enabled, it attempts to download the channel from the beginning. However, that apparently collides with "Only Recent", when it previously did not: It detects that the video it just tried to download is too old, and therefore the processing of the channel should stop.

Disabling the chunk downloads helper lets it work normally. And while having both enabled is probably a misunderstanding on my part, maybe this behavior should at least be explicitly documented.