identifying standard

[caldo_de_cana]

Hello
I am making a program that saves the video transmitted from an MSN messenger webcam.
so far I've found out it sends the data in HTTP (up to 1460 bytes per packet). Then these packets can be regrouped to form new packets ranging from 300 to 10k bytes. (which i assume are the video images)
I have not been able to identify in which format the data comes in. the only thing in common those packets have are a header that is about 44 bytes long. I haven't found any information as to what encoding/compression that might be.
It uses the Logitech Video IM Companion builtin msn messenger.

I want to help from people that can point me to docs that will help me identify the compression/encoding, and how to decompress it, or any program that can read it.

I'll post the headers from the 3 first packets, and what I think some parts mean:
18 00 40 01 F0 00 01 00 FC 0C 00 00 4D 4C 32 30 0C 00 00 00 76 82 09 01 00 01 94 11 40 01 F0 00 61 74 65 64 00 00 00 00 1C 00 30 2E

18 00 40 01 F0 00 00 00 D4 07 00 00 4D 4C 32 30 0C 00 00 00 F6 84 09 01 00 01 94 11 40 01 F0 00 61 74 65 64 01 00 00 00 1C 00 30 2E

18 00 40 01 F0 00 00 00 F4 07 00 00 4D 4C 32 30 0C 00 00 00 23 86 09 01 00 01 94 11 40 01 F0 00 61 74 65 64 01 00 00 00 1C 00 30 2E

40 01 is width
f0 00 is height
f4 07 is packet size
there is also a 4-byte timestamp.
01 00 probably mean 256 colour

[Skylark]

I would post this on the microsoft tech forum

[jtowler]

Would love to help you...but. What am I looking at? Is this a capture? Is this the Ethernet header? The IP header? The TCP (because you said http) header? or the payload?

More detail please.

[caldo_de_cana]

this is the payload of the http packets.
The data on the packets is 1460 bytes long, except for the last part of a video image packet. so if a video packet is 5k, it will have 3 full http packets (1460) plus what is left to complete 5k.
every video packet has these headers.
is there a place I can post the whole packets?

[caldo_de_cana]

also, where can I find this microsoft tech forum?

[Mattia.m78]

MSN uses the Logitech Mimic encoding.
You could find a lib and other info searching "libmimic" on google.

I have a question for you..
Do you know wich is the protocol used by MSN Messenger 7.5 in VideoCalls?
I think it is an interleaved audio/video codec developed by Logitech.
It uses udp datagrams (not rtp).

Someone could help me?
Thanks,
Mattia

[andrew_791]

nice thread. was really interesting. that program seems to be awesome.


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