I recently discovered I can use text-to-speech on my android smartphone to listen to pdf files. The result is intelligible, and speed can be adjusted. The robotic sound doesn't bother me too much, in fact in some sense it's easier to follow because of the lack of emotional noise. I wouldn't recommend listening to fiction with it though.

Audiobooks are obviously superior, but unfortunately limited in variety. My eyes tire faster than my brain too. If I could use Anki with my eyes closed, that would be awesome.