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
This reverts commit ad4beac464.
That commit wasn't as advertised; I had several other changes mixed in my
working copy. I'd also copied a working copy from one path to another, and
it turns out the cmake build subdir was still referring to the original, so
I hadn't realized this commit didn't even build. :(
This isn't as much of a speed-up as you might imagine; most of the large HTTP
content was mmap()ed files which are relatively efficient. The big improvement
here is that it's now possible to serve large files (4 GiB and up) on 32-bit
machines. This actually works: I was just able to browse a 25-hour, 37 GiB
.mp4 file on my Raspberry Pi 2 Model B. It takes about 400 ms to start serving
each request, which isn't exactly zippy but might be forgivable for such a
large file. I still intend for the common request from the web interface to be
for much smaller fragmented .mp4 files.
Speed could be improved later through caching. Right now my test code is
creating a fresh VirtualFile from a database query on each request, even
though it hasn't changed. The tricky part will be doing cache invalidation
cleanly if it does change---new recordings are added to the requested time
range, recordings are deleted, or existing recordings' timestamps are changed.
The downside to the approach here is that it requires libevent 2.1 for
evhttp_send_reply_chunk_with_cb. Unfortunately, Ubuntu 15.10 and Debian Jessie
still bundle libevent 2.0. There are a few possible improvements here:
1. fall back to assuming chunks are added immediately, so that people with
libevent 2.0 get the old bad behavior and people with libevent 2.1 get the
better behavior. This is kind of lame, though; it's easy to go through
the whole address space pretty fast, particularly when the browsers send
out requests so quickly so there may be some unintentional concurrency.
2. alter the FileSlice interface to return a pointer/destructor rather than
add something to the evbuffer. HttpServe would then add each chunk via
evbuffer_add_reference, and it'd supply a cleanupfn that (in addition to
calling the FileSlice-supplied destructor) notes that this chunk has been
fully sent. For all the currently-used FileSlices, this shouldn't be too
hard, and there are a few other reasons it might be beneficial:
* RealFileSlice could call madvise() to control the OS buffering
* RealFileSlice could track when file descriptors are open and thus
FileManager's unlink() calls don't actually free up space
* It feels dirty to expose libevent stuff through the otherwise-nice
FileSlice interface.
3. support building libevent 2.1 statically in-tree if the OS-supplied
libevent is unsuitable.
I'm tempted to go with #2, but probably not right now. More urgent to commit
support for writing the new format and the wrapper bits for viewing it.
