Blackmagic Forum

I am trying to send the output of the 2110 Converter to a Synamedia vDCM. It works well for the video (1080p). The vDCM however does not like the audio. It refuses to process the audio multicast stream and the GUI shows strange errors.

Checking the SDP file reveals that the converter puts 64 audio tracks into the stream:

v=0
o=- 3739873105 1 IN IP4 10.245.141.100
s=Blackmagic von KS OUT 6 zu 2110/Audio
t=0 0
m=audio 16390 RTP/AVP 97
c=IN IP4 239.255.3.218/255
a=source-filter:incl IN IP4 239.255.3.218 10.245.141.100
a=rtpmap:97 L24/48000/64
a=ptime:0.125
a=ts-refclk:ptp=IEEE1588-2008:10-B3-D6-FF-FE-A4-45-D7:127
a=mediaclk:direct=0
a=ssrc:2887703542 cname:2BA94175A043494FA87C87662206785D

I assume that this is the reason for the problem; the vDCM does not expect more than 16 channels, because this is the maximum number of channels supported by SDI.

Does anybody know how to tell the converter to use the actual number of channels or at least limit the number of audio channels to 16?

Hi. Fortunately, I don’t have any equipment with Blackmagic’s SMPTE 2110 version. But at first glance, there seem to be two issues here:

The 3x3G 2110 IP Converter uses PCM Audio Conformance Level C. Your Synamedia vDCM may only be compatible with Level A or B.

The SDP describes the stream incorrectly. Logically, there’s no way it could contain 64 audio channels, so the Synamedia vDCM deems it incompatible and ignores it.

The most reasonable course of action would be to contact Synamedia vDCM support to resolve this issue and clarify which audio parameters are supported.

Thank You very much for your explanation!
Meanwhile I found out that the vDCM is in fact capable of dealing with the Blackmagic 2110 Converter audio. It is, however, only possible with some dirty tricks, like defining the channel layout before you connect the stream, as otherwise the GUI will not work correctly. I believe that this is something that needs to be corrected on the Blackmagic side, as it is totally useless to advertise 64 channels, when you cannot have more than 16 channels anyway.
Also, I found the main reason why the vDCM does not like the Blackmagic audio: The audio is not correctly synced; the timestamping is sometimes several seconds (not milliseconds!) off, if you use external PTP sync for the converter. Switching to internal (i.e. make the converter the Grandmaster even it makes no sense) and back to external repairs the a/v sync.
But this is something I need to sort out with the Blackmagic support, as well as the 64 channel issue.