30fps at d1 res(740x480) record for all 16ch pc impossible!

[griffonsystems 0]

can someone prove to me that this is possible. you see marketing or even tech specs that say 480fps and resolutions of 740x480 but i know the path from the compression card to the harddrive cannot support this data load no matter what compression you are using.

 

if someone can explain the data stream on a 16bit bus or prove to me that this is possible i would appreciate it. the 16channel system(mpeg4) that i sell does d1 704x480 at 7.5fps for all 16 and does lowres at 30fps for all 16.

 

my guess is that if you break the 16 into 4 cards maybe that will give you the ability to do 30fps/d1/16 - but i havent tested that out

 

thx

 

pg

[rory 0]

I know im getting 13 cameras at 30fps in 640x480, and i had it set to 720x480 in the beginning and was getting exactly that.

[kandcorp 0]

Our PC DVR's say they can accomplish that but have not tested it out yet. Will try and let ya know.

[Thomas 0]

740 x 480 x 6 (Pixels x RGBvalue+location value) = 2131200 bits. Note we're in bits still.

 

2131200/8 = 266400 Bytes (8 bits is one byte in PCs. Keep in mind this is an arbitary number)

 

266400/1024 = 260.15624 KB (Bytes to Kilobytes)

 

260.15624/1024 = .2540588 (KB to MB, guys note I'm rounding here but not in the calulator. We now have the value of one frame, both fields.)

 

.2540588 * 30 = 7.621765 (Frame size * the number of bytes per frame)

 

7.621765 * 16 = 121.94824 (Frame size at 30 fps * the number of cameras.)

 

Allow for 5 mb/s overhead....and 126.94 mb/s. PCI bus (33 mhz) is rated for 132 mb/s. 66 mhz allows for 264 mb/s.

 

Keep in mind, this is raw data rather then MPEG/Compressed data.

[rory 0]

and in english ..?

[JMANOFNVS 0]

Hey Thomas where did you get that formula? So in geek theory 30fps at 740 x 480 for 16 cameras is possible. How much do the different compressions change that?

[Thomas 0]

Compression would lower the number. And the numbers I got from an SDK.

[griffonsystems 0]

so thomas is saying a non compressed video stream of 16 cameras is possible so is the issue the compression card not being able to compress that size data stream in real time the issue? im trying to get thru the grey area thats all over this industry

 

thanks in advance for the help

[rory 0]

the grey area is in the Linux RTOS as far as I can see ..

[Jasper 0]

Thomas explained that real well.

 

The PCI bus is one bottleneck, but the hard drive needs to be able to write that fast as well. You would need a RAID arrary in order to write information at the full speed of the PCI BUS.

 

The newest 10k Raptor hard drives are doing around 76MBps (they claim 84) while the PCI BUS can handle 133MBps across the 32 bit data path.

 

That is why the newer PCI Express BUS is going to really help with pushing more data across the BUS. And the wider data path a SATA connection offers in combination with faster data transfer rates of newer hard drives coming to market should eliminate this problem all together.

[G22 0]

Would SCSI be much faster?

[Jasper 0]

Would SCSI be much faster?

 

You would still be limited by the data transfer rate of the hard drive even if it connected directly to the motherboard. Hard drives just don’t transfer data fast enough yet to keep up with large amounts of data.

 

If it was short bursts of data, buffering could help, but with continous flow of video that is not really an option.

 

You can use RAID to dramatically increase your ability to write out data faster to the hard drives though.

 

Just noticed: 740x480, shouldn't that be 720x480?