The Javascript is pretty amateurish I'm sure but at least it's something to
iterate from. It's already much more pleasant for browsing through videos in
several ways:
* more responsive to load only a day at a time rather than 90+ days
* much easier to see the same time segment on several cameras
* more pleasant to have the videos load as a popup rather than a link
that blows away your position in an enormous list
* exposes the fancier .mp4 generation options: splitting at lengths
other than the default, trimming to an arbitrary start and end time,
including a subtitle track with timestamps.
There's a slight regression in functionality: I didn't match the former
top-level page which showed how much camera used of its disk allocation and
the total duration of video. This is exposed in the JSON API, so it shouldn't
be too hard to add back.
I had an assert that fired in this case, dating back to when I hadn't plumbed
Result returns through much of .mp4 construction. Now I have, so there's no
excuse in having an assert here. Change to an error return, and tweak it to
not fire in the zero-duration case.
Also fix a problem in the test harness; I hadn't finished converting it for
multi-recording tests, and it was returning the wrong recording.
Because of that, I seem to have stumbled across a related problem in which
asking for zero duration of a non-zero duration recording will return a
recording::Segment with no frames, which will cause panics because its
corresponding .mp4 slices are zero-length. I just adjusted the panic message
here; I'll follow up with changes to address that.
The advantages of the new schema are:
* overlapping recordings can be unambiguously described and viewed.
This is a significant problem right now; the clock on my cameras appears to
run faster than the (NTP-synchronized) clock on my NVR. Thus, if an
RTSP session drops and is quickly reconnected, there's likely to be
overlap.
* less I/O is required to view mp4s when there are multiple cameras.
This is a pretty dramatic difference in the number of database read
syscalls with pragma page_size = 1024 (605 -> 39 in one test),
although I'm not sure how much of that maps to actual I/O wait time.
That's probably as dramatic as it is due to overflow page chaining.
But even with larger page sizes, there's an improvement. It helps to
stop interleaving the video_index fields from different cameras.
There are changes to the JSON API to take advantage of this, described
in design/api.md.
There's an upgrade procedure, described in guide/schema.md.
