First off, the YouTube channel caveat. Even good Youtube channels aren't scholarly sources, because the format doesn't allow for proper citations. However, the fact that these are -videos- allows the presenter to illustrate something (movmement in armour, for instance) much more effectively than text or pictures could. There's two good channels about Medieval armour and combat that I would recommend:

• Schola Gladiatoria by Matt Easton is a HEMA-focused channel that has a lot of good pieces about weapons and armour (I can't speak to the actual martial arts - I study HEMA to contexutualize armour and weapons, not the other way around). His segments with Dr. Tobias Capwell of the Wallace Collection are particularly good.

• Knyght Errant by Ian La Spina is a more focused channel on military equipment in the late 14th and very early 15th century (the era of Agincourt). It includes a series of videos on each part of the harness (suit) of armour worn by men at arms.

As a bonus, here is my favorite Youtube video of armour, from the Musee du Moyen Age. Though the video doesn't have a full 'works cited' and discussion of methods the armour used (the one with the Great Bascinet) is discussed in detail in a recent paper on armour mobility, which I'm hoping to talk about this Saturday as part of our 'what are you reading' feature.