I am hoping someone has seen this is can maybe help?
We are currently experiancing a problem at a customers site who are running a handful of C20's as well as some Polycom endpoints. The issue only appears to be with point to point calls between C20's and VSX6000's but the video from the C20 will not display on the VSX end (you see a rainbow effect on the screen, screenshot below). We can see that the VSX is using H264 CIF and suspect that the C20 cannot support CIF using H264. Maybe a solution is be to force the C20's to use H263 but I'm not sure if this is possible? The issue does not occur if the call is connected via a Codian bridge.
Has any one seen this issue before or have any suggestions for a work around please?
Thanks in advance.
I may have answered my own post, by running the API command xconfiguration Experimental CapsetFilter: "H.264" I was able to turn off H.264 and force the C20 to make a H.263 call. This appears to have worked and from the websnap video, I think, can be seen in both directions. Not ideal I guess but it's a work around of sorts and goes some way to answering the issue.
If anyones has a suggestion for a better solution it would be most welcome?
If I understood correctly, the distorted image appears on VSX6000A's screen, right?
I think about two possibilities to this problem:
- C20 is not encoding the video sent correctly
- VSX6000A is not decoding the received video correctly
To me, I guess that the problem is on VSX6000A. Because C20 normally supports all resolution when using H.261, H.263, H.263+, H.264. I think that C20 is sending a resolution/bit rate higher than VSX6000A can supports, so that VSX6000A does not decode the image correctly and shows a distorted image on screen.
According to Polycom's documentation, VSX6000A supports H.264 only with bit rate up to 768kbps. So, I ask you to enable H.264 again in C20, then you make a call again and post here the call statistics taken from C20. I would like to see which are the bit rate and resolution of the video sent by C20. Probably, if you decrease the bit rate of the call into C20 and configure a value less than 768kbps, the problem will be solved.
Maybe you can try disabling some of the extra H264 modes...
xConfiguration Experimental CapsetFilter: "H.264RCDO;H.264NIL"
I am not sure this will work but worth a try
Thanks for your help. That’s correct the rainbow image is taken from the VSX end. I have tried the call at 768 and 512 and the result is the same. I also suspect the VSX cannot decode the signal.
The call placed at 768kbps
C20 call stats
Polycom call stats (note no receive video format)
The call placed at 512kbps
C20 Call Stats
Polycom Call Stats (no received video)
I also see Johns response recommending the xconfig Capset command which I did try before with some degree of success. It basically forces the connection to be made using H.263 and a clear image can be seen. So whilst the limitation is at the VSX end by effectively dumbing down the C20 a connection can be made.
Not ideal but a work around never the less. I will check to see if the VSX is on the latest version etc, maybe there have been some advancements in that area.
This is strange for me "512x288@17p". Why are you using this resolution? Cannot you try to use another resolution? Maybe Polycom's codec is having some problem do decode H264 with this resolution, perhaps.
This is not something we've puposely set, is this something to do with the optimization setting I wonder?? Where can you specify the res to use, thought this was mainly an auto negotiated setting??
In addition - it looks like the 512x288 is basically just widescreen CIF (16:9) whereas the VSX is using 352x288 (4:3)
So I guess the question is how do I set the C20 to use CIF 4:3?
You can change the resolution, look this:
But I think that it's not possible to change the aspect ratio, because the video source (Tandberg Camera) is "16:9" definition, not a "4:3" definition.
So under optimal definition as suspected and 512x288 is the lowest it will go and it's widescreen.
It looks like the software on the VSX has an upgrade available so I will do this and hopefully that will address it.
All good and thanks again for your help.
From testing that we've done (admittedly many years) in the past, we've only been able to get the VSX series endpoints to decode CIF and 4CIF resolutions using h.264, as well as their NTSC equivalents. They do not appear to be able to decode widescreen resolutions at all.
Th problem with this is that the h.241 standard (the standard for negotiating h.264 transmission on an h.323 call) does not allow you to specify discrete resolutions or aspect ratios that you can decode, only a maximum image size. Therefore according to what is signalled in the capability set it there's nothing to say that the VSX cannot decode w288p, for example.
The reason that this works with the Codian MCU is that this product recognises that the far end is a Polycom VSX from the signalled vendor and product ID and applies a special workaround for it. This has been implemented after the capabilities of the VSX were explored during lab testing, this is not something that can be determined from the standard signalling unfortunately, so is not something that every endpoint should be expected to support 'out of the box'.