Try out Shokz bone conducting headphones. They are awesome, you can hear the world around you, and the app has a vocal booster mode that makes listening to podcasts much better. It works really well on my 1.5 hour bike commute in traffic with road noise, and I can still hear the cars passing by.

While 720 is the technical low end of HD, 1920x1080 is generally what most people mean when referring to High Definition