Eirteam ffmpeg extension blocks when waiting for url

[daan-laixer]

avformat_open_input blocks when reading from an url and the server is not streaming, blocking the extension and in turn pixelbot.

Options:

• use the abort blocking function callback/interrupt to continue when blocking too long
• handle setup in another thread
• use "dummy" in avformat_open_input like EIRTeam uses and make a _stream_read_callback for avio_alloc_context