SVGA and XGA video encoding

[cribbinsb]

I've been doing some interoperability testing of various codecs using SVGA and XGA - 800x600 and 1204x768 H.263+. This is just for a single video channel I'm not talking about a H.239 / duovideo content channel here. Several endpoints I've tested with advertise the ability to receive H.263+ at 800x600 @ 10fps, and 1024x768 @7.5fps.

My first question is that I've found that although our polycom FX H.323 with latest software (6.0.1FX 24 March '04) advertises SVGA and XGA receive, when I actually send it video in those formats the decode comes out badly corrupted. Identical media to either a Tandberg 6000 or an Aethra endpoint is just fine. Has anyone had hi-res video decoding ok on a poly FX?

My second question is that all the endpoints I've tested with only do high resolutions at the low framerates I already mentioned. Is anyone aware of any codecs that will do SVGA, XGA H.263 at a decent frame rate? Or even one that will transmit 4CIF at 30fps?

[trapehzoid]

I've been doing some interoperability testing of various codecs using SVGA and XGA - 800x600 and 1204x768 H.263+. This is just for a single video channel I'm not talking about a H.239 / duovideo content channel here. Several endpoints I've tested with advertise the ability to receive H.263+ at 800x600 @ 10fps, and 1024x768 @7.5fps.

My first question is that I've found that although our polycom FX H.323 with latest software (6.0.1FX 24 March '04) advertises SVGA and XGA receive, when I actually send it video in those formats the decode comes out badly corrupted. Identical media to either a Tandberg 6000 or an Aethra endpoint is just fine. Has anyone had hi-res video decoding ok on a poly FX?

My second question is that all the endpoints I've tested with only do high resolutions at the low framerates I already mentioned. Is anyone aware of any codecs that will do SVGA, XGA H.263 at a decent frame rate? Or even one that will transmit 4CIF at 30fps?


I haven't had specific problems with my FX.. but it can only do it via the Visual Concert box. You have a way of doing it without? You should also try changing what display you are putting it on. If you are using the internal VGA out vs the VisualConcert and check that for differences.

No one is doing 30fps at those higher resolutions.. the compression just isn't good enough to cram that much data down the pipe.. plus all the additional memory it would take to handle that much info. Newer codecs could probably do 4CIF.. but no way on the PC resolutions, at least at the bandwidths we normally are using.

The only place it should be noticable is if you are trying to do movies.

Whats the application you are trying to do that demands more?

[cribbinsb]

I don't have a visual concert box. I've been using the standard svideo out of the FX. Of course I understand that a regular TV certainly can't display XGA at full res and it's debatable whether it has the resolution to display SVGA- nevertheless I would expect the TV encoder chip to make something sensible of it. For instance our TB6000 displays XGA on either it's svideo or VGA outputs just fine (naturally the VGA looks far better!). I have tried using the FX's VGA out but I can't figure out how to get it to drive the main display out of VGA instead of svideo. Any ideas here?

As for high framerates + high resolution. SVGA has only a 20% greater area than 4CIF, XGA 95%, so with some modern codecs supporting up to 4 Mbps there is plenty of bandwidth available. I agree it's pointless endcoding something at a higher resolution than the source material so, short of using an HDTV camera, you don't need these resolutions for a single stream. However for streams composed of several lower-resolution images you can see a big difference.

[trapehzoid]

I don't have a visual concert box. I've been using the standard svideo out of the FX. Of course I understand that a regular TV certainly can't display XGA at full res and it's debatable whether it has the resolution to display SVGA- nevertheless I would expect the TV encoder chip to make something sensible of it. For instance our TB6000 displays XGA on either it's svideo or VGA outputs just fine (naturally the VGA looks far better!). I have tried using the FX's VGA out but I can't figure out how to get it to drive the main display out of VGA instead of svideo. Any ideas here?

As for high framerates + high resolution. SVGA has only a 20% greater area than 4CIF, XGA 95%, so with some modern codecs supporting up to 4 Mbps there is plenty of bandwidth available. I agree it's pointless endcoding something at a higher resolution than the source material so, short of using an HDTV camera, you don't need these resolutions for a single stream. However for streams composed of several lower-resolution images you can see a big difference.

The FX will not send high resoution if the far end doesn't have it connected if I recall. The VGA output on the FX can only be used for graphics output.. not main output.

I know the tandberg will send high resolution all the time (if the far end supports it) and leaves it up to the reciever to figure out what to do with it. I think the FX will not send high resolution to a FX without a visual concert. How are you putting the PC input into the system? The software based visualconcert? If the FX isn't sending as SVGA or whatever, and just 4CIF.. the image will be poorer, even tho you are only watching it on a TV.

This is one of the issues with the FX.. you can't really send native PC format stuff without visual concert cleanly. Technically you can, if you jump through hoops, but if you just want A to B, its not as easy as it is on a tandberg.

As for the PC formats only being so much % more then 4CIF.. you'll notice none of the major codecs out there do 30fps at 4CIF either.. only 7.5 or 15fps. Its not just about bandwidth to compress down to.. its bandwidth and memory within the codecs. Encoding at 30fps simply means alot more data flowing around and with larger images to work with.. with a XGA image being 7x as much data as a CIF image... put one and one together.

[cribbinsb]

I think there's some confusion here (it could be on my part though!), let me summarise the situation again. I'm trying to get the FX to decode & display the XGA or SVGA video I'm sending to it, I'm not (at the moment) particularly interested in what the FX is transmitting. I'm generating the XGA H.263+ that I am sending to the FX myself (via my own PC based endpoint). If I send the same video to other endpoints they decode it fine whereas it's recognisable but badly garbled when decoded on the FX (and viewed on a TV via svideo). I am trying to understand why the FX is advertising SVGA and XGA H.263+ receive capabilities, yet it doesn't seem to be working correctly when I use them. Any help you could give me here would be much appreciated. Would a "visual concert" help? I've never used one so I don't really understand what it does.

I have to say I am still not convinced that there should be much technical reason any more why codecs these low framerates. For instance 30FPS XGA is 30MB/s of data which is <1% of the memory bandwidth of a modern PC. To prove the point the test endpoint I'm using (which isn't even very optimized) on a 2.4GHz P4 PC can send and receive 30fps XGA H.263+ and it uses a shade under 50% CPU doing so. Sadly the only thing available for it to talk to is itself! On the DSP side a DM642 or Equator BSP-15 has no trouble encoding MPEG-2 at full D1 (in security cameras!) so why not 30fps 4CIF H.263? The same DSPS can also decode HDTV 720p WM9. I am hopeful that future software upgrades will at least take the new endpoints (e.g. vsx7000) to 30fps 4CIF.

[MACC the AVCOtek]

I believe (about 75% sure) that you need a Visual Concert on the receiving end to decode the native XGA or SVGA that is being sent to the FX. Otherwise, you're just getting 4CIF (if that).

All in all, the Visual Concert is a confusing piece of equipment and is a poor choice for integrating PC graphics with VTC. One is better off using a Tandberg codec. Polycom has realized this and integrated PC graphic support with their new VSX 8000. I haven't seen it in action yet though so can't comment on whether it works well or not.

[tom9933]

I think there are a few issues here; I’ll try to summarize what I suspect is going on.
To start with there are a couple of ways to send a high resolution image to a codec. The simplest is to send a 4CIF image at a very low frame rate. This is done by several manufactures on what they call their high resolution or snap shot camera. In most cases the codec sends a single frame of video at the 4CIF resolution (704 * 576), hence the term Snap Shot. This generally works well when the receiving system only has a video monitor but if we are talking about a computer signal then it’s still a bit low. BTW I think the old PCSNAP utility from Polycom used 4CIF to capture the desktop image of a pc in software.
The next way to go is to use a dual stream format such as Duo Video, People + Content or H.239. In this situation the goal is to take a signal from a computer or other high resolution source and send it to the far site in its original resolution. As you might guess this means sending a signal of much higher resolution and hence more bandwidth/compression. Most systems support resolutions up to 1280 * 1024.
The visual concert box is used on Polycom systems to encode the computer signal as either People + Content or H.239 on the newer systems. BTW I’ve seen the Polycom send content as 4CIF to some legacy systems. The brick does have its own VGA output and I have heard that the output on the brick looks a bit better than the output on the FX/4000. In our case we didn’t see a big difference and we typically use the 15 pin output on the back of the codec. I agree the external brick works better on a conference room table then in an integrated system (due to mount ability/ergonomics) but the quality of the image produced is very good. As for the comment about the VSX 8000 the quality of the H.239 input/output on the 8000 seems similar to that on a VSX 7000 with the brick.
As mentioned earlier, the signal from the video output on the codec is severely down converted so high resolution graphics on that output will look bad, but they still typically look better than the output from a typical ($1k or less) scan converter. Also on the VS4000/FX the VGA output can only send out graphics, but in the 7.0 release the VSX line also has the capability of putting video on that output. We have used this on dual monitor setups and it works quite well.
So I guess my question to you would be what exactly are you trying to send to the codecs? Is it just a 4CIF image or are you sending the data as a content stream? It sounds like you should be trying to use a content stream.
Thoughts, corrections…..

[cribbinsb]

Thanks for your input! In fact it's not a 4CIF image I'm trying to send but a real XGA resolution video stream. This is just a straightforward single channel video call, no dual streams involved. The polycom has advertised the ability to receive XGA H.263+ in it's main stream just like it advertises the ability to receive regular CIF H.263. I can verify by looking at the H.323 signaling that I am correctly opening a transmit channel to the polycom at XGA, and I know the XGA H.263+ media I am sending is good (as the same media is decoded ok by a tanderg 6000 or aethra endpoint). But the polycom decodes the video all messed up!

I'm not sure if any endpoints will actually send SVGA or XGA resolution on their main (non-content) channel so is it possible that this feature has never been tested (and just doesn't work) on the polycom FX?

[Yukikaze]

If you disable dual monitor on your Tandberg it will send pc images on the main channel(If you have the presenter option).

[tom9933]

Ok then that’s an interesting concept, probably true that the average user would never test such a thing. I wonder if the VSX would have the same problem and I also wonder if this would be a way to send HD at lower frame rates. While this is probably not an issue for most I think the medical folks would very interested.
If you want to test this with a VSX PM me and Ill send you an address.

[cribbinsb]

I already tried with a VSX 7000 but I found that it doesn't advertise receive or transmit capabilities for anything above 4CIF :( Plus as an aside has anyone noticed the awful quality of the VSX 7000's transmitted 4CIF (very low frame rate, bizarre interlacing artifacts)? It's a shame as I really like the VSX7000 in most other respects.

As I previously mentioned I did manage to get a Tandberg 6000 and an Aethra endpoint to receive and decode the XGA just fine. I also intend to try with an IPower and a VTEL but I haven't had a chance yet.

[Sean Lessman]

I'm not sure if any endpoints will actually send SVGA or XGA resolution on their main (non-content) channel so is it possible that this feature has never been tested (and just doesn't work) on the polycom FX?

The TANDBERG endpoints support the same resolutions on both the main and the secondary H.239/DuoVideo streams. We do support XGA on both.

Sean

[cribbinsb]

Hi Sean. Do you know how I can get my TB6000 to transmit XGA in the main channel?
Ideally I'd like to make a single stream (no h.239) XGA call from the TB to my polycom FX. Is there a way to get the TB to use it's VGA in (or even better VNC) in the main stream?? Thanks!

[Sean Lessman]

Hi Sean. Do you know how I can get my TB6000 to transmit XGA in the main channel?
Ideally I'd like to make a single stream (no h.239) XGA call from the TB to my polycom FX. Is there a way to get the TB to use it's VGA in (or even better VNC) in the main stream?? Thanks!

Hi,

There are two modes on the TANDBERG unit for DuoVideo/H.239: Automatic and Manual (found in the Presentation settings). If you leave it on automatic, the TANDBERG will automatically start Duo/H.239 whenever ANY content source button is pressed and the far end supports either Duo or H.239. If you do not want the TANDBERG to start Duo/H.239 when pressing the PC button, change the Duo setting to 'manual'. Now the PC will transmit on the main channel.

This will work with the iPower but not the FX. I believe the FX only sends/receives XGA in P+C mode. You have to first support P+C to send or receive it.

Sean

[cribbinsb]

Thanks for the help Sean, I'll give it a go. It's interesting that you say you don't think it will work with the FX as that's precisely what I want to try. As I've mentioned in a previous post the FX does advertise XGA receive in it's standard H.323 capability set so it'll be interesting to see if the TB6000 opens an XGA channel and if so, whether it works.

[Sean Lessman]

Thanks for the help Sean, I'll give it a go. It's interesting that you say you don't think it will work with the FX as that's precisely what I want to try. As I've mentioned in a previous post the FX does advertise XGA receive in it's standard H.323 capability set so it'll be interesting to see if the TB6000 opens an XGA channel and if so, whether it works.

Good luck. :-)

I can do a quick trace tomorrow and look at the capset. Last I checked, the best you got was 4CIF.

Sean

[cribbinsb]

I did what you said and sure enough the TB6000 transmits XGA fine in it's main channel. However although XGA works to every other endpoint you are right that it only opens 4CIF to the polycom FX. I've looked again at the capset and XGA is definitely there. It's possible I'm making a mistake here so I'll get our H.323 expert to look at it tomorrow. Another (less likely) possibility is that Tandberg have also noticed that main channel XGA decode on the FX is bugged so have put in a work-around? As I say it's unlikely but not impossible, it certainly wouldn't be the first time I've seen vendors working around each others bugs!

[Glen Sykes]

One of the problems with the FX, and indeed the EX is that in order to decode custom resolutions, it requires the visual concert (as stated above).

Becuase the FX cannot support single screen operation with the visual concerts VGA connector as the main monitor output, you will not see XGA content on a single monitor FX.

The best you could hope for is that the FX will support H.239 and you connect an XGA monitor to the visual concert in order to view the high resolution 2nd stream. I'd say it would be unlikely that Polycom will develop single screen XGA operation on the EX and FX. Also, I have spoken to polycom in the past about the VGA output on the set top box itself, the upshot was that the main unit was not capable of decoding custom resolutions without the visual concert. Essentially, the VGA output on the FX is pretty much redundant.

[George]

Another (less likely) possibility is that Tandberg have also noticed that main channel XGA decode on the FX is bugged so have put in a work-around? As I say it's unlikely but not impossible, it certainly wouldn't be the first time I've seen vendors working around each others bugs!
I'd definitely be interested in knowing if that was indeed the case.

Interesting....

[Sean Lessman]

I did what you said and sure enough the TB6000 transmits XGA fine in it's main channel. However although XGA works to every other endpoint you are right that it only opens 4CIF to the polycom FX. I've looked again at the capset and XGA is definitely there. It's possible I'm making a mistake here so I'll get our H.323 expert to look at it tomorrow. Another (less likely) possibility is that Tandberg have also noticed that main channel XGA decode on the FX is bugged so have put in a work-around? As I say it's unlikely but not impossible, it certainly wouldn't be the first time I've seen vendors working around each others bugs!

Our H.323 experts have looked at it several times in the past and its something Polycom will have to resolve :-)

We (TANDBERG) have not introduced any workarounds for XGA.

Sean

[MACC the AVCOtek]

I can do a quick trace tomorrow and look at the capset.

Hey Sean, how do you do this? I'm interested in learning!


(maybe this ought to be in another thread though, huh?)

[trapehzoid]

Hey Sean, how do you do this? I'm interested in learning!


(maybe this ought to be in another thread though, huh?)

if its h323 its very easy... just type 'syslog on' in the dataport/telnet and then place your call. Be sure to have a text capture running first, as tons of data will fly by.

However, you need to understand a bit about h245 to make conclusions from it. But the 'as is' information is there.

[cribbinsb]

Good to see that VTCtalk is back!

Sean (and others): you might be interested to hear that we finally got to the bottom of the reason why the TB6000 will not open XGA in the main channel to the Polycom FX, and it's a good one! Our experiments show that if the ProductId in the H.225 VendorIdentifier section starts with the string "Tandberg" then the FX doesn't advertise the SVGA and XGA CPF capabilities!!!

If you establish an XGA call between the Tandberg's and the Polycom FX via an intermediate relay (with a different VendorIdentifier!) then it turns out that the Poly FX shows the same corruption decoding the media that it did when decoding the media that I originally tried sending it from my test tool. Unbelievable.