Basically libavcodec57 and it's dependencies are not available in Buster.
$ sudo apt install python-sipsimple blink
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have
Can you paste the logs
> On 14 Oct 2019, at 18:34, David Keller wrote:
>
> Could you please update the repository (at ag-projects.com/debian)
>
> It won't install on latest stable Debian release (which is Buster) because of
> broken dependencies.
>
> Thanks and best regards,
> Dave
>
>
