Well some music file can be infected mp3 I think, but mostly it is the medial players that are exploited, so it is important that you keep it fully up to date.
Image files can also be infected and .jpg is one, the most common for non-slr professional digital cameras. It is possible that your SD card in the camera could get infected and I don't know if that could subsequently infect the .jpg files. If you scan them after you transfer them to the HDD folder, you could exclude that folder from on-demand scans, as avast by default would scan .jpg files before they are opened (because there is a risk of them being infected).
I would suggest that you only run a Standard sensitivity scan (which only scans file which are at risk from infection) and without archives, this should lessen the scan duration with limited risk.