Chroma subsampling isn't the only way to compress video footage. It's also possible to compress individual frames, and in one of two ways.
Intra-frame compression compresses each frame individually. This is the best route if you want top quality frame-by-frame.
Inter-frame compression doesn't store whole frames. Instead, it only stores the changes since the last 'key' frame. It's still possible to reconstruct individual frames, but now it has to be done by combining the frame data with the last (or the next) key frame.
Not every camera will offer you the choice, and the terms may change slightly each time. The choice may be expressed as 'All-I' (intra-frame) and 'IPB' (inter frame) compression.
