Trouble setting up stream component

I am trying to add the stream component to hass, for connecting my RTSP-enabled doorbell.
After adding it to the configuration.yaml, the error log shows:

Setup failed for stream: Requirements for stream not found: ['av==6.1.2'].

According to, this issue can be fixed by installing the right dependencies:

sudo apt-get install -y python-dev pkg-config libavformat-dev libavcodec-dev libavdevice-dev libavutil-dev libswscale-dev libavresample-dev libavfilter-dev

However, this command fails with:

E: Failed to fetch  404  Not Found 

I can confirm the link is indeed dead, so it appears that there is an issue with my package repo in Raspbian.

I am running Raspbian Buster on a Pi 4 (virtualenv). To be precise:

uname -a
Linux raspberrypi 4.19.75-v7l+ #1270 SMP Tue Sep 24 18:51:41 BST 2019 armv7l GNU/Linux

Anyone here who encountered the same problems and managed to fix it?
I already tried to install ffmpeg and others from source, but this did not help much.