CCTV Question - 1080P Cameras Into 720P DVR. Will It Work?

[thecctvcompany 0]

Hi

Can one connect a 1080P SDI camera to a 720P DVR and still get acceptable recording performance?

 

I know that the answer should be 'yes' but am not sure of the technical implications here.

 

Obviously 1080P has a higher bitrate than 720P to start with.

Seeing that SDI DVRs do the decoding at the DVR end, it means that the DVR has to work hard and becomes more expensive as the channels rise.

However, if one has a 720P DVR and it receives a 1080P stream, does it just drop frames, or does it do the decoding and simply convert the 1080P stream to an internal 720P stream?

 

What are the reasons why one would not want to do this?

 

The cost of a 1080P DVR is quite a bit higher than a 720P DVR. However, there is little difference in cost between 720P and 1080P SDI cameras. So it makes sense for us to buy 1080P SDI cameras so that they can be connected to a range of DVRs

 

Thanks!

[SunnyKim 2]

For me, answer is no. The chipsets on the PCB board might not be programmed to accept the bigger sized video, most likely. But 1080P DVR can take 720P camera, most likely.

[thecctvcompany 0]

We have tried it and it does work.

We tested it on 4 channels only but now want to move to a 16 channel system.

ie, we ran 4 x 1080P SDI cameras into a 720P DVR and it worked fine.

 

We are more interested in the technical reason why and why not this may or may not be a good idea.

Also what the risk issues are when we connect 1080P cams to a 720P DVR

We just don't want to embark on a technology mismatch that will come and bite us later.

 

Yes, I take the point about the chipsets and in the end this may be a capability of the DVR itself.

It may be that some suppliers' DVRs will simply not work and others will.

 

We are keen to know if anyone else has tried this and what the outcome was.

[SunnyKim 2]

Good to know,

Let me explain a bit more on the chipsets on the PCB.

1. The SDI decoder (receiver) must be using BT1120 format to feed

video data (either of 720P or 1080P) into a CoDec(compression/De-comp), at back end.

2. The DVR software is set to be able to configure to accept 1080P.

-- auto configuring video size of input camera.

-- probably, the SDK from the CoDec chipset maker maintains one set of SDK to cover all size of video input, all kinds of DVR sets.

3. The CoDec is always set to run such a high clock rate for processing the 1080P (bigger than 720P). This may shorten the life time of DVR or causing over heating issue. Who cares!!

4. 1080p needs the processing power, at least, twice than that of 720P.

5. But the Codec itself is limited in number of total frames per second to be processed

for compression and decompression & display, at the same time.

So you must have to define encoding frame rate and decoding frame rate on your own

within this budget.

6. Did you test 16 Ch X 960H, if the DVR carries 16Ch input ports?

Must be working?? My guess is yes, in terms of its processing power of the CoDec.

Then you may try on 16 Ch X1080P at a quarter FPS or less.

I guess The CoDec chip can most likely accept 8 inputs, max, in case for HD sized video.

But they may not have put the enough number of the SDI receiver chip sets, at the front,

to get in 8 Ch or 16 Ch HD SDI cameras for cost saving.

 

Please let me know.

[thecctvcompany 0]

SunnyKim, that is an intelligent reply. Thanks for that.

 

It is what I suspected.

We suspect that the 720P DVR is able to decode the 1080P stream but at a reduced frame rate.

So instead of getting maybe 25fps, we may need to throttle back to 12 or 15fps which will not make a big difference anyway in the site where this will be installed.

 

From what you say, there seems to be two stages in the decoding process?

The video receiver and the SDI decoder.

You may need to assist with clarifying this....

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The raw bitstreams comes in at 1080P on the BNC connectors at the back.

Then each BNC connector feeds into a SDI decoder ('BT1120')?

Or are 2 or more BNC inputs combined into a single SDI decoder?

 

Then the DVR software sits on top of this hardware and manages the receiving streams and passes it to both the HDD and monitor screens.

 

Am I correct in thinking then that the capability to push 1080P into a 720P DVR depends on the manufacturer of the DVR and what provision they have made for high speed decoding?

[SunnyKim 2]

We suspect that the 720P DVR is able to decode the 1080P stream but at a reduced frame rate.

So instead of getting maybe 25fps, we may need to throttle back to 12 or 15fps which will not make a big difference anyway in the site where this will be installed.

I do not agree with you at this point. They must have encoded (compressed) 1080P at a reduced frame rate. Because the CoDec chipset knows what it can do or what it can not do. The decoding (de-compressing) uses the compressed bit stream, as they are stored (reduced frame rate already). As long as application accepts OK, then OK for all others.

 

From what you say, there seems to be two stages in the decoding process?

The video receiver and the SDI decoder.

You may need to assist with clarifying this....

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I may say that the terminology is confusing. Please allow me to clarify as following.

There are 2 kinds of chipsets in the most of DVRs.

One is the video decoder chipset that demodulates the modulated signal from camera. In this case, HD-SDI -receiver or decoder is sitting at the front end of PCB board. Do not get confused that most DVR box carries input ports at its back side panel.

The other is CoDec chipset which serves as main CPU of DVR box. Some may call SoC or Back End Main processor. Compression/ Storing the compressed bit stream file to HDD/ Reading back the bitstream for decompressing and play-back to monitors, all kinds of things needed for DVR features.

HD-SDI receiver chipset is a sort expansive. For 8 channel HD-SDI inputs, they must have 8 -single channel chipset or 2 sets of 4 Ch (quad) receiver chip set. It seems that the receiver HD-SDI chipset is capable of decoding both 1080P and 720P, running at each different clock rate.So you are lucky. Just several years ago, only 720p was affordable and 1080P was very expansive.

 

The raw bitstreams comes in at 1080P on the BNC connectors at the back.

Then each BNC connector feeds into a SDI decoder ('BT1120')?

Or are 2 or more BNC inputs combined into a single SDI decoder?

Then the DVR software sits on top of this hardware and manages the receiving streams and passes it to both the HDD and monitor screens.

Am I correct in thinking then that the capability to push 1080P into a 720P DVR depends on the manufacturer of the DVR and what provision they have made for high speed decoding?

It could be more clear if you say " raw video data" in stead of raw bitstream, even though HD-SDI encoded (modulated) format is in Bit Serial form. The "bitstream" is more associated with Compressed Bitstream, say H.264, MPEG.

The HD SDI receiver chipset re-formats the incoming bit serial-raw video data into a common video data format, BT1120. Most of CoDec chipset,sitting, at the back end, can accept BT1120 formatted video data as a standard video data.

In the market, there are single channel HD-SDI decoder chipset and a four channel HD-SDI chipset, so called Four in One(quad) chipset.

Yes, DVR software sits on the CoDec chipset which embeds a high performance CPU.

As the final answer, decoding speed is to depend on the encoded frame rate, in most applications.

[thecctvcompany 0]

SunnyKim, thank you for your input and technical explanation.

This has been most helpful to us.

 

Thanks again for taking the time out to engage with us and deal with the technical issues we are interested in understanding!

We really appreciate this

 

Regards

Clive