Per request of a cool frood, here is my brain dumb of this project.

    The carcam started off as a solar powered squierrel camera.  However the
adafruit components I bought only outputed 2.2-2.7V and wasnt enough to power
the camera.  As long as I had all the parts, i decided to make a dashcam.

    First probelm i had.  I think i blew out my GPS MCU when soldiering it.  It
was my first soldiering job in  a loooooong time.  I ended up buying new equipment
and setting up my dedicated work table again.  After replacing the MCU I got better
results.

    With the GPS MCU, it takes like 20 minutes for it to get initial sync.  You
need a good line of sight to the sky, or your just beating your head against the
wall.   After that, syncs are pretty fast.  One thing that ancedotally helped 
was the 40dB passive antenna.  Even though the vendor's site says you need an
active antennae.

    I screwed up and didnt realize the PPS line had to be soldiered to a GPIO
header on the board, and the raspbian boot config set as the clk pin.

    NTP config was suprsingly hard to get a clear cut answer on how to setup.
Eventually google found me someones random blog post.  However the PI is terrible
at maintaining clock sync.  I dont think it has a bios battery, so powered off
it comes up drastically wrong.   This requireed me to put a while loop in my 
scripts that checks until skew is less then some arbitrary amount (5 seconds?).
Then the scripts will continue on.  Otherwise iwas getting wierd effects. Especially
when I was trying to get the subtitles to render live.  Imagine the click jumping
backward and forward in time a full day, when the video itself is  only a minute
long.

    Video/Subtitle nightmare.  So initially i just used the ffmpeg ability to point
at a single txt file, and every frame it re-reaads it.  And hard subs it in.  this
is exactly what i wanted.  You can box, and resize, and do positioning.... The 
Pi Zero is to weak.  FFmpeg transcoding the video at like 0.2x.  Longer it runs
worse it gets.

    Switched over to softsubs.  All my attemtps to updatethe subtitles alongside
the video streaming ended in bizzare behaviour.  For most part, first video segment
would work  for 7-10 seconds, and everything after that would be blank.  Even
if you `ffmpeg -i video.mkv subitle.srt/vtt`, it ends up being empty.  I think
ffmpeg reads the subtitle file once at some random point per segment, and thats it.
Whcih is wierd, since it doesnt wirte out the subtitles to the container to the end.
Well atleast for matroska, because if u ctrl+c the process before then, vlc complains
saying the subtitle stream is unrecongizable or corrupt.

    So in the end, i generate the subtitel file in parrallel with the saving the video,
in 60s chunks.  Then after the raspivid exits, we delete a lock file, signaling to start
generating a new nmea/subtitle file.  While background stream coping the video segment
and its subtitle files.  My inital tests show the skew is <2 seconds. which is 
fine for my shits and giggles.