Livestreamer video timer when writing to file

[mateon1]

Apart from "Written x bytes" it would be an improvement to add how much video was downloaded (A timer).
For example: Written 123456789 bytes, 2 minutes, 16 seconds of video.

This would be useful for YouTube videos and Twitch past broadcasts, possibly for other streaming video sites as well.

[chrippa]

In c389337 I improved the status line a fair bit, but the requested feature to display video time is not there, but instead replaced with the elapsed time. This is because to get the actual video time we would have to decode the video, which is not something we can nor wish to do.