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OpenH323/OPAL & Polycom Accord MCG 100 video

This is a short update to all interested parties:

I've been experimenting with H.263 and RFC 2429 and have made the following observation:

Everything works just fine until a frame exceeds the size of one RTP packet. I've been running a conference at 64kbit/s and QCIF, and the picture quality was horrible, but it worked. As soon as the frame gets bigger than one RTP packet, the picture freezes immediately. So there is hope...

From what I know so far, this MCU seems to be VERY picky about the RTP payload formats. The RFC 2429 packetizer used does nothing harmful AFAIK: Every packet starts at a GOB boundary and the P bit is set. All packets following the first one have an extra picture header included.

On the data received from this MCU, only the first packet has the P bit set, the following packets haven't. Eventually, I can write an own packetizer that matches this particular behaviour. We'll see...

Regarding RFC 2190: If I recall correctly, the ffmpeg implementation usually sends the first packet as Mode A, followed by Mode B packets. This seems to work with this MCU. The RFC2190 packetizer I use sends Mode B packets only when needed, thus only if a GOB exceeds the size of 1438 bytes. Since the H.263 bitstream created by QuickTime always includes the GOB start code, I prefer sending Mode A packets. Eventually, only the packetization scheme used by the ffmpeg implementation does to work.

What remains the problem using H.261 (both VIC and QuickTime) remains unclear so far

Am 3. Feb 2006 um 16:39 schrieb Hannes Friederich:


Am 3. Feb 2006 um 15:44 schrieb Guilhem Tardy:

Hi,

When testing XMeeting.app, the same codecs work on Tandberg devices,
other MCU's, Microsoft NetMeeting as well as Polycom PVX. So, there
is no doubt that the codecs work and can be decoded.

This only shows that it can be decoded. THe codec (encoder) may still not be
standard compliant.

I know. On the other side, H.261 (VIC) does not work with this MCU either. In addition, what relates to "standard compliant"?
The H.263 encoder used is just plain H.263 without any extra options. But if you can tell me whether the codec is standard compliant or not, I'd be happy to hear...

I have seen that on the Interoperability list on http://
www.salyens.com/interop/index.html, this MCU is listed as not to work
with H.263 due to some problems in call setup. So far, I haven't
heard anything from Guilhem Tardy, whom I've contacted off-list.

That was *yesterday*, and for your information I have a full-time job (I can
even say, day and night) with deadlines looming.

Therefore, I make 2 lists: simple and complex questions. Yours went into the
latter, and will be answered with the others in that list in chronological
order.

Thanks for your patience.

I have no problems with that, and I fully understand your reasons... I was just thinking that eventually other people have some information about this as well. I just wanted to avoid replies of the kind "ask Guilhem Tardy, he is the expert in this area", but eventuelly my english wasn't clear enough on this... 

Guilhem.

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