I use ZM with h.264 passthrough in mocord mode.
Most of videos have length = "Section length" from monitor settings. Actually, this is documented behavior, but from my point of view this solution is bad.
Here is common video structure (0 - alarmed frames, - is not)
-----------------------------------------------------------00--------------------------------------
When you playback the video, you don't know where alarmed frames are placed. In the best case (ZMNinja) you have overlay highlighting alarmed frames, however you always must navigate to the alarmed frames manually. As workaround, it's possible to decrease section length, however here we start to loose h.264 backend advantage - less stress on server filesystem.
I think the situation can be improved if on alarm, previous event forcefully closed. It this case we have the following:
-------------------------------------------------------><--prev_frames-00-post_frames-><--------------------------------------------------------------------------
The advantage: h.264 backend everywhere, alarmed frames are placed like in modect mode.