This is more sophisticated than the current implementation. It's an attempt
to address the problems created by the 9 seconds/day of drift I'm seeing for
long-running streams.
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 crate is a slightly-more-polished and MIT-licensed version of
resource.rs. So far it has one advantage: running the tests doesn't
require RUST_TEST_THREADS=1.
The benchmarks now require "cargo bench --features=nightly". The
extra #[cfg(nightly)] switches in the code needed for it are a bit
annoying; I may move the benches to a separate directory to avoid this.
But for now, this works.
This is a significant milestone; now the Rust branch matches the C++ branch's
features.
In the process, I switched from using serde_derive (which requires nightly
Rust) to serde_codegen (which does not). It was easier than I thought it'd
be. I'm getting close to no longer requiring nightly Rust.
It would be nice to build on stable Rust. In particular, I'm hitting
compiler bugs in Rust nightly, such at this one:
https://github.com/rust-lang/rust/issues/38177
I imagine beta/stable compilers would be less problematic.
These two features were easy to get rid of:
* alloc was used to get a Box<[u8]> to uninitialized memory.
Looks like that's possible with Vec.
* box_syntax wasn't actually used at all. (Maybe a leftover from something.)
The remaining features are:
* plugin, for clippy.
https://github.com/rust-lang/rust/issues/29597
I could easily gate it with a "nightly" cargo feature.
* proc_macro, for serde_derive.
https://github.com/rust-lang/rust/issues/35900
serde does support stable rust, although it's annoying.
https://serde.rs/codegen-stable.html
I might just wait a bit; this feature looks like it's getting close to
stabilization.
Seeking in Chrome 55 wasn't working. It apparently sends If-Match requests
with the correct etag, which Moonfire NVR was incorrectly responding to with
"Precondition failed" responses. Fix and test that.
I hadn't noticed the problem in earlier versions of Chrome. I think they were
using If-Range instead, which is already tested and working.
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.
* new, more thorough tests based on a "BoxCursor" which navigates the
resulting .mp4. This tests everything the C++ code was testing on
Mp4SamplePieces. And it goes beyond: it tests the actual resulting .mp4
file, not some internal logic.
* fix recording::Segment::foreach to properly handle a truncated ending.
Before this was causing a panic.
* get rid of the separate recording::Segment::init method. This was some of
the first Rust I ever wrote, and I must have thought I couldn't loan it my
locked database. I can, and that's more clean. Now Segments are never
half-initialized. Less to test, less to go wrong.
* fix recording::Segment::new to treat a trailing zero duration on a segment
with a non-zero start in the same way as it does with a zero start. I'm
still not sure what I'm doing makes sense, but at least it's not
surprisingly inconsistent.
* add separate, smaller tests of recording::Segment
* address a couple TODOs in the .mp4 code and add missing comments
* change a couple panics on database corruption into cleaner error returns
* increment the etag version given the .mp4 output has changed
I found this while bringing db.rs's test coverage up to the old
moonfire-db-test.cc. I mistakenly thought that in SQLite, an ungrouped
aggregate on a relation with no rows would return a row with a null result of
the aggregate. Instead, it returns no rows. In hindsight, this makes more
sense; it matches what grouped aggregates (have to) do.
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).
The old release on googlecode.com now 404s, so out-of-the-box builds were
broken. The releases on github have a slightly different file structure, so it's
more than just a change of URL. I upgraded from 1.7.0 to 1.8.0 in the process.
* typo: the subtitle should use its own mdhd, not alias the video one
* use 64-bit ints for the edit lists; the 32-bit values overflow at 13.25 hours
* use etags that reflect the edit list
I'm seeing what is possible performance-wise in the current C++ before
trying out Go and Rust implementations.
* use the google benchmark framework and some real data.
* use release builds - I hadn't done this in a while, and there were a
few compile errors that manifested only in release mode. Update the
readme to suggest using a release build.
* optimize the varint decoder and SampleIndexIterator to branch less.
* enable link-time optimization for release builds.
* add some support for feedback-directed optimization. Ideally "make"
would automatically produce the "generate" build outputs with a
different object/library/executable suffix, run the generate
benchmark, and then produce the "use" builds. This is not that fancy;
you have to run an arcane command:
alias cmake='cmake -DCMAKE_BUILD_TYPE=Release'
cmake -DPROFILE_GENERATE=true -DPROFILE_USE=false .. && \
make recording-bench && \
src/recording-bench && \
cmake -DPROFILE_GENERATE=false -DPROFILE_USE=true .. && \
make recording-bench && \
perf stat -e cycles,instructions,branches,branch-misses \
src/recording-bench --benchmark_repetitions=5
That said, the results are dramatic - at least 50% improvement. (The
results weren't stable before as small tweaks to the code caused a
huge shift in performance, presumably something something branch
alignment something something.)
Now it's possible to quickly determine what calendar days have data and then
query recordings for just the day(s) of interest with their returned
{start,end}_time_usec.
The helper isn't used yet. The goal is to export this on /camera/<uuid>/ as
described in a TODO in design/api.md.
The next step is to keep MoonfireDatabase::CameraData::days up-to-date:
* Init: call on every recording (replacing the current aggregated query with
a recording-by-recording query)
* InsertRecording, DeleteRecordings: call for added/removed recordings
then return it from GetCamera and pass it along to the client in
WebInterface::HandleJsonCameraDetail.
* If the end of a segment is between samples, the last included sample will
have a shortened duration.
* If the beginning of a segment not on a key frame (aka sync sample), the
prefix will be included but trimmed using an edit list. (It seems like a
ctts box might be able to accomplish the same thing, fwiw.)
