As described in design/time.md:
* get the realtime-monotonic once at the start of a run and use the
monotonic clock afterward to avoid problems with local time steps
* on every recording, try to correct the latest local_time_delta at up
to 500 ppm
Let's see how this works...
The test ensures it solves the problem of the initial buffering throwing off
the start time of the first segment.
Along the way, I tested and fixed the new TrailingZero flag; it wasn't being
set.
This is as described in design/time.md. Other aspects of that design
(including using the monotonic clock and adjusting the durations to compensate
for camera clock frequency error) are not implemented yet. No new tests yet.
Just trying to get some flight miles on these ideas as soon as I can.
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.
This test is copied from the C++ implementation. It ensures the timestamps are
calculated accurately from the pts rather than using ffmpeg's estimated
duration. The Rust implementation was doing the easy-but-inaccurate thing, so
fix that to make the test pass.
Additionally, I did this with a code structure that should ensure the Rust
code never drops a Writer without indicating to the syncer that its uuid is
abandoned. Such a bug essentially leaks the partially-written file, although a
restart would cause it to be properly unlinked and marked as such. There are
no tests (yet) that exercise this scenario, though.
I should have submitted/pushed more incrementally but just played with it on
my computer as I was learning the language. The new Rust version more or less
matches the functionality of the current C++ version, although there are many
caveats listed below.
Upgrade notes: when moving from the C++ version, I recommend dropping and
recreating the "recording_cover" index in SQLite3 to pick up the addition of
the "video_sync_samples" column:
$ sudo systemctl stop moonfire-nvr
$ sudo -u moonfire-nvr sqlite3 /var/lib/moonfire-nvr/db/db
sqlite> drop index recording_cover;
sqlite3> create index ...rest of command as in schema.sql...;
sqlite3> ^D
Some known visible differences from the C++ version:
* .mp4 generation queries SQLite3 differently. Before it would just get all
video indexes in a single query. Now it leads with a query that should be
satisfiable by the covering index (assuming the index has been recreated as
noted above), then queries individual recording's indexes as needed to fill
a LRU cache. I believe this is roughly similar speed for the initial hit
(which generates the moov part of the file) and significantly faster when
seeking. I would have done it a while ago with the C++ version but didn't
want to track down a lru cache library. It was easier to find with Rust.
* On startup, the Rust version cleans up old reserved files. This is as in the
design; the C++ version was just missing this code.
* The .html recording list output is a little different. It's in ascending
order, with the most current segment shorten than an hour rather than the
oldest. This is less ergonomic, but it was easy. I could fix it or just wait
to obsolete it with some fancier JavaScript UI.
* commandline argument parsing and logging have changed formats due to
different underlying libraries.
* The JSON output isn't quite right (matching the spec / C++ implementation)
yet.
Additional caveats:
* I haven't done any proof-reading of prep.sh + install instructions.
* There's a lot of code quality work to do: adding (back) comments and test
coverage, developing a good Rust style.
* The ffmpeg foreign function interface is particularly sketchy. I'd
eventually like to switch to something based on autogenerated bindings.
I'd also like to use pure Rust code where practical, but once I do on-NVR
motion detection I'll need to existing C/C++ libraries for speed (H.264
decoding + OpenCL-based analysis).
Scott Lamb