Decent DVR system that integrates easily with HA

I want to buy a multi camera DVR system that will allow for such things as "when the door bell rings, send me a snapshot/20 second video of the front porch". Of course I will take care of the detecting the doorbell ringing, but how would I tell the DVR system to send me a snapshot or even better, a short video of say 20 seconds before the doorbell was rung? I would need a DVR that has the means to store video in a way that I could request a specific time frame and it would need a way of packaging and delivering the video. Ideally I would like to keep it in the $200-$300 region.
 
I am sure there are other ways of doing such a thing and I am open to that as well.
 
Thanks in advance!
 
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Most firmware based DVR / CCTV systems utilize propietary firmware and do not publicize the API or a mechanism of changing the software.
 
You can purchase a digital DVR or IP HD camera with Zone (analog switch inputs) today.  These are over $200 and typically do not include hard drives. 
 
You can also purchase a Cosco or other big box package with cameras and DVR.  Typically those are proprietary with little or no information relating to their firmware. 
 
Going with software will let you do more with a DVR system.
 
Here utilize a Linux software based program called Zone Minder.
 
I started tinkering with this software before digital IP cameras and continue to use it today with digital IP cameras.
 
I played with a variety of different cameras over the years and this software allowed me to do that.
 
I have a firmware based Grandstream DVR but have never done anything with it yet.
 
IP HD camera choices are plentiful and cheap these days.
 
Going with software you can typically utilize a variety of different mfg cameras.
 
I would venture over to this forum and ask the same question ==> CCTV Forum

Thanks for the tip! After looking at SW based systems, I see that there has been a lot of progress with Raspberry Pi systems. I think I will try that first.

Zone Minder works with the RPi.
 
About 3 years ago a peer in the UK wanted access to an Axis servers (SD).  He installed Zone Minder on an RPi2 and was able to access the Axis SD CCTV server just fine.  Not sure if he did any DVR functions with it though.
 
Here have been using the RPi's for all sorts of things.  Today one is a slave Z-Wave (with GPIO) device combo 1-Wire temperature and humidity network, X10 and UPB slave.  It is using a POE connection for power.  For KODI it wasn't fast enough (but that is me).  Another ARM based device; old now is doing irrigation software (firmware) only with analog connectivity (via USB) to wired irrigation solenoids, 1-wire and RF remote for checking irrigation zones / sprinkler heads.
 
Here is a quickie snapshot of zmNinja Pro which is an iPhone / tablet interface for Zone minder.
 

 
Have a look at this...
 
What is motionEyeOS?
motionEyeOS is a Linux distribution that turns a single-board computer into a video surveillance system. The OS is based on BuildRoot and uses motion as a backend and motionEye for the frontend.
 

Another option might be to look into a device which already does this.  I know that older Axis 2400 and 241Q units would let you send pics (pre and post trigger) on an external contact closure into the device (I had this give me pics when the doorbell would ring at my old house a while ago).
 
I'm thinking HikVision might have this capability included as well (and a lot cheaper than Axis products).  I have the DS-2CD2142F unit, and I'm pretty sure I read something about input contact closure capability that could fire a capture rule to send an email.