[BUG] Since v1.13.0, the UI completely hangs after a few seconds of a download

[EDM115]

2025-09-30_16-37-40.mp4

As you can see, it stops logging. The UI is unresponsive (including the window controls) but what's running behind (yt-dlp or ffmpeg) keeps working, and the progress indicator on the taskbar is still alive. It is also impossible to alt-tab back to it.
The logs return at the "Adding metadata" step roughly.
edit : the window stayed unresponsive after the second video download

• System : Windows 11 24H2
• yt-dlp version : stable@2025.09.26 (D:\EDM115\Programmes\Python312\Scripts\yt-dlp.exe)
• ffmpeg version : 8.0-full (C:\Users\EDM115\AppData\Local\Microsoft\WinGet\Links\ffmpeg.exe, is a symlink to C:\Users\EDM115\AppData\Local\Microsoft\WinGet\Packages\Gyan.FFmpeg_Microsoft.Winget.Source_8wekyb3d8bbwe\ffmpeg-8.0-full_build\bin\ffmpeg.exe)
• Cube YouTube Downloader version : 1.13.0

[database64128]

Thanks for the detailed report! The memory usage of youtube-dl-wpf.exe also looks suspiciously high in task manager.

The logs return at the "Adding metadata" step roughly.

The UI becomes responsive again at around the "Adding metadata" step? That's interesting. Can you enable log files in settings, and attach the log file along with a timeline of when it became unresponsive and when it became responsive again?

[EDM115]

20250930.log

Here you go, search for //! for my comments.
to be sure I deleted all the app files and re extracted but it didn't changed anything

[database64128]

Cannot reproduce on my system. 😕

I wrote a log replay tool to test with your log file. Can you also test with the tool to see if the issue can be consistently reproduced on your system? You can download the tool from https://github.com/database64128/youtube-dl-wpf/actions/runs/18171244467, go to settings, change backend path to the tool, and add the path to the log file as the first startup argument. Then you can type anything as the video link and hit enter.

[database64128]

BTW YouTube also recommended "Spotify Lossless has a problem" to me and I watched it too 😆

[EDM115]

aaand it also happened with the logs replay, not at the same points but it did. UI hang and memory usage spike

https://drive.google.com/file/d/1wLcct4bSCfWC9SzfwbMtoOByCsy6cLH-/view?usp=drive_link

[EDM115]

UPD : I was able to get the UI to be responsive again by reducing the number of shown log entries from 1024 to 64. The memory usage also stays below 120 Mb.
I suspect that the logs panel might be redrawn entirely at every new log entry, causing lag and the UI can't keep up, idk. seems the most likely so far

upd 2 : althought not the best source of info, ChatGPT does seem to agree with some hints, might be useful ? https://chatgpt.com/s/t_68de61bb5d988191abec7eaece02033c

[database64128]

I suspect that the logs panel might be redrawn entirely at every new log entry, causing lag and the UI can't keep up, idk. seems the most likely so far

I don't know how a TextBox handles content updates, but the app has been using the TextBox this way since the very beginning. And before I added "Max log entries" in v1.11.0, the growth of log messages used to be unbounded. Back then I used to do lots of downloads on a slow laptop, and I've seen first hand how the UI gradually slowed to a crawl, as tens of thousands of log messages accumulated. The window's frame rate would drop over time, but it wouldn't become completely unresponsive, and you can see in task manager that a single thread ate up a whole CPU core.

Based on the videos you posted, I don't think this is what's happening on your system. Besides, that part of code barely changed between v1.12.0 and v1.13.0. How come you only have this issue with v1.13.0?

Can you capture a memory dump while the UI is unresponsive? You can go to the details tab in task manager, right click youtube-dl-wpf.exe, and select "Create memory dump file".

[database64128]

I was able to get the UI to be responsive again by reducing the number of shown log entries from 1024 to 64.

I added a button for clearing the log viewer a few days ago. Would it keep the UI responsive if you keep the number of shown log entries at 1024, but clear the logs once in a while? Or maybe just keep clicking the clear button to see if it locks itself up?

The fact that the UI becomes responsive again after the backend process exits, makes me suspect this is some kind of concurrency, thread safety bug.

[EDM115]

Can you capture a memory dump while the UI is unresponsive?

• Memory dump 1 (went to 250~ish Mb) : https://drive.google.com/file/d/1YuDmdrWjpnO2A5AfZV6wUbVdRVugBI_R/view?usp=drive_link
• Memory dump 2 (went to 3~ish Gb) : https://drive.google.com/file/d/148zRT-2ySwdj-e9YCtH1zgcysUVgUVvR/view?usp=drive_link

[EDM115]

Would it keep the UI responsive if you keep the number of shown log entries at 1024, but clear the logs once in a while? Or maybe just keep clicking the clear button to see if it locks itself up?

Test from the build of b4ac6b9 with a log size of 1024.
The issue doesn't occur when I clear the logs. When I let them in at some point it does start to lag until it hangs, seems to correlate with the memory increase ?
https://drive.google.com/file/d/1zYHoxfg0MqhWRIp1bsKykXBo1p_RCIyF/view?usp=drive_link

[database64128]

When I let them in at some point it does start to lag until it hangs, seems to correlate with the memory increase ?

Interesting. I didn’t observe any significant increase in memory usage when I replayed your log file.

Which binary package did you download? Was it the larger self-contained build?

[EDM115]

yes it was the youtube-dl-wpf-b4ac6b93250dd7f31861793f76f236b65a27c171-windows-x64