What is the best software for streaming PC gameplay to Twitch?

You can download a plugin called DirectShow Audio Source, but you're only given options to use audio inputs (mic, speakers, etc...). You cannot simply select a wav or mp3 file to loop (going AFK or BRB for example).

Quick Sync is hardware video encoding and decoding technology that's comparable in speed, compression ratio and quality to x264. Since Quick Sync is a dedicated hardware core on the processor die, it allows for faster and more power efficient video processing.

OBS has over 20 plugins to choose from, including one's that allow adding video files and any other media supported by VLC as a source, integrating Twich chat and switching scene depending on what window is in focus.

Wirecas has support for rare advanced functionality such as IP cameras, remote desktop capture, 3d virtual sets, image slideshow, scoreboards, projectors.

A paid license is required to use XSplit for any commercial purposes. The personal license is $4.95/mo and the premium license is $8.95/mo.

A paid license allows streaming to multiple services at the same time.

XSplit has a source plugin store (with about 5 plugins) that add functionality such as whiteboards, image slideshows and video playlists.