[Theora-dev] Re: PC-based video server

[John Kintree]

On Wednesday 26 January 2005 02:20 pm, Andrey wrote:
> >  I've seen pretty good quality theora format video at less than 1 Mbps.
>
> What was the resolution/frame/rate/type of the movie.

A sample video can be downloaded, using BitTorrent, from www.theora.org. 
 It's in the Contents section on the left side of the page, and labeled "CC
 spots." What you actually get is three short videos for a total of about 20
 MBytes. In my opinion, the video named "Mixtape.small.ogg" is the best. 
 It's a two minute, fun video that uses 8.8 MB of storage, and looks to be
 about 352x240 and 30 fps.

> What you mean by "after" - buffering the streams in memory? I thought OS
> can handle it on it's own.

I meant that the video from camera1 would be saved at 00:00, again at 00:10,
and every ten minutes on an automated basis.  The video from camera2 would be
saved at 00:01, again at 00:11, and so on.  So, video from camera2 would be
saved one minute "after" video from camera1.  Spacing the timing of saving
the video from the different network camera is just a way to avoid trying to
write too much data to the hard drive(s) at the same time.

> Initially that server should do 2 (or 3) parallel jobs:
> 1 - uninterruptedly store all the high-res video on disks (DVR);

That's relatively easy.

> 2 - serve lower resolution video from live data in parallel with recording
> with minimal delay.

This is the tricky part because, as you describe below, the theora format
video needs to be transcoded into something like MJPEG format AND streamed at
the same time.  I really don't know what kind of CPU power you need to do
that.  If it was a single network camera, I suspect that a high-end PC today
could do the job, but 10-20 network cameras, that almost sounds like a
cluster, or a rack, of PCs to me.

I think the only way you can proceed is to record some video with your
 network camera while the FPGA encodes it into theora format.  It could be as
 simple as someone walking or running in front of the camera.  That will give
 you the bits per second and bytes per minute for the quality that your
 customers require.  Then you will also be able to determine how much
 processing power you need to convert that theora format video realtime into
 MJPEG format.

> Actually it will be possible to use 2 different servers for these 2 tasks
> if needed - anyway there will be multicast stream.
>
> and only the 3rd job will be to serve the stored video.
>
> > If people wanted to watch the live video, they would just go to the
> > address of that network camera, right?  So, the PC-based video server
> > would not be required to do much, if any, streaming video.  People who
> > want to watch the stored video could just download the desired files,
> > right?
>
> Not exactly - and here is the main point.
>
> At the first stage all this high-performance GNU/Linux + Theora stuff is
> confined to server+cameras. External interface of the system as a whole
> will be MJPEG (other standard software codecs possible), "server push"
> that majority of the video management software used in videosecuruity
> business - the software they are currently using and don't want to get rid
> of immediately. So the proposed server can be plugged in their system and
> behave as a set of regular network cameras, not as a server+cameras.
>
> That, from one side, will not scare off customers who got used to some
> system immediately and will significanbtly simplify our job - security
> systems have much more than cameras alone (i.e. other sensors) and many
> companies work for a long time in this area and I don't think it is
> possible to design something similar in short time and using limited
> resources.
>
> So I consider such server as intermediate step to get Theora into this
> application area. It will be then next step to get rid of intermediate
> formats.

Considering the constraints of the legacy software your customers are using,
what you are considering makes sense to me.  I hope all of it can be done at
a practical price.  Eliminating the intermediate formats would simply things
a lot.  Good luck.
John

-------------------------------------------------------