There's a lot of work left to do on this:
* important latency optimization: the recording threads block
while fsync()ing sample files, which can take 250+ ms. This
should be moved to a separate thread to happen asynchronously.
* write cycle optimizations: several SQLite commits per camera per minute.
* test coverage: this drops testing of the file rotation, and
there are several error paths worth testing.
* ffmpeg oddities to investigate:
* the out-of-order first frame's pts
* measurable delay before returning packets
* it sometimes returns an initial packet it calls a "key" frame that actually
has an SEI recovery point NAL but not an IDR-coded slice NAL, even though
in the input these always seem to come together. This makes playback
starting from this recording not work at all on Chrome. The symptom is
that it loads a player-looking thing with the proper dimensions but
playback never actually starts.
I imagine these are all related but haven't taken the time to dig through
ffmpeg code and understand them. The right thing anyway may be to ditch
ffmpeg for RTSP streaming (perhaps in favor of the live555 library), as
it seems to have other omissions like making it hard/impossible to take
advantage of Sender Reports. In the meantime, I attempted to mitigate
problems by decreasing ffmpeg's probesize.
* handling overlapping recordings: right now if there's too much time drift or
a time jump, you can end up with recordings that the UI won't play without
manual database changes. It's not obvious what the right thing to do is.
* easy camera setup: currently you have to manually insert rows in the SQLite
database and restart.
but I think it's best to get something in to iterate from.
This deletes a lot of code, including:
* the ffmpeg video sink code (instead now using a bit of extra code in Stream
on top of the SampleFileWriter, SampleIndexEncoder, and MoonfireDatabase
code that's been around for a while)
* FileManager (in favor of new code using the database)
* the old UI
* RealFile and friends
* the dependency on protocol buffers, which was used for the config file
(though I'll likely have other reasons for using protocol buffers later)
* even some utilities like IsWord that were just for validating the config
Before, I had a gross hardcoded path in moonfire-db.cc + a hacky
Recording::sample_file_path (which is StrCat(sample_file_dir, "/", uuid),
essentially). Now, things expect to take a File* to the sample file directory
and use openat(2). Several things had to change in the process:
* RealFileSlice now takes a File* dir.
* File has an Open that returns an fd (for RealFileSlice's benefit).
* BuildMp4 now is in WebInterface rather than MoonfireDatabase. The latter
only manages the SQLite database, so it shouldn't know anything about the
sample file directory.
