aMSN webcam quality

[baron]

Hi, I've noticed that when using aMSN to send webcam the quality doesn't seem to be as good as in MSN.

I did a little investigating, and it seems that while in aMSN source the webcam DLL exposes a method to change the quality, I don't think (from a quick look, I'm not familiar with TCL) that the calling code is setting the quality, so it's going to the default, which is zero quality. MSN messenger seems to set this to a higher quality (I just did a test and this was at 4500 on a test file).

Am I barking up the wrong tree here .. or could this be a slight oversight? If it was unintentional it would be very easy to fix.

/edit
Well as no one has answered .. here's how I fixed on my build (0.97RC1):
1) Went into msncam.tcl
2) Found proc Grab_Windows (I'm on windows, you would fix the proc for your platform)
3) Added a line to set the quality

set encoder [::Webcamsn::NewEncoder HIGH]
setObjOption $socket codec $encoder

#add this line
::Webcamsn::SetQuality $encoder 4500

I've never used tcl/tk but this seems to be working according to my tests.

[Kreuger]

I thought the quality was dependant on the webcam and their internet connection?! Interesting to know that the client can also affect it.

[kakaroto]

Hi baron,
Noone ever complained.. but hey, you must be right!
At first, when I saw the post, I thought "oh no, not another one complaining about the webcam", then I thought you were refering to the quality of the captured image, and I was thinking you were mad.. then I understood you were talking about the quality of the mimic encoder, and it makes sense. I guess we thought that the default quality used by libmimic was the same as the one used by MSN. And iirc, I did test different qualities and saw no difference, so I thought that it doesn't make any difference.
I just checked, and the default quality is indeed 0 (defined in mimic-private.h).
Anyways, I now changed this in SVN revision 9119 for all platforms.
Thanks for finding this.
@Kreuger: the quality of the image is dependant on the webcam, the quality of the *encoded* image is dependent on the codec used (the one used by msn is mimic and it has a configurable quality for the encoding), and the framerate is dependent on the internet connection.

[baron]

glad to have helped!

[square87]

Hi Baron
I knew about that behavior, but i didn't know how to resolve it.
How do you find that value?

Anyway thanks!

[baron]

Hi Baron
I knew about that behavior, but i didn't know how to resolve it.
How do you find that value?

Anyway thanks!

Hmm, well it's easy for me as I can debug through my ML20viewer lol ... but for mortals:

If you look through a captured .cam file in a hex editor, and find an 'ML20' fourcc in the stream. This is part of the external frame header:

   unsigned char m_ucHeaderSize;// 0
   unsigned char m_ucIsPauseFrame; // 1
   unsigned short m_usWidth; // 2
   unsigned short m_usHeight; // 4
   unsigned short m_usIsKeyframe; // 6
   unsigned int m_uiPayloadSize; // 8
   unsigned int m_uiFCC; // ML20 // 12
   unsigned int m_uiUniqueRandomID; // 16
   unsigned int m_uiTimestamp; // 20

Just past this you get to the frame data, and bytes 2-3 of this are the quality setting of the internal frame header, see:

http://wiki.multimedia.cx/index.php?title=ML20

So the 2 bytes for the quality start at 10 bytes past the end of the ML20 fourcc. '9411' would indicate 4500 (1194 in hex). You may also be able to step through the webcam DLL source if you have that handy.

Incidently, it is possible that the MSN client adjusts this value, however in the captures I've tried from MSN clients on other machines it has always been 4500 ... whether that is a function of my bandwidth I don't know.

If you need to capture aMSN's output you can use Wireshark or MSN webcam recorder. I run MSN and aMSN at the same time on the same machine camming from one to the other to test.

[kakaroto]

hehe, baron, great method for finding out the quality used by MSN.. I would have dug into its code instead of looking at the generated cam stream, lol..
in any case, I just took a quick look into the webcam dll of msn, and it seems to be using '4500' for something when creating the cam stream.. I guess it's the quality... (it actually calls some unknown function giving it a few paramters.. 'ML20' as the first parameter, 4500 as the 3rd.. So we can assume it's hardcoded (otherwise, it wouldn't appear hardcoded in the code, it would be 'calculated' depending on the bandwidth you have).

[square87]

Hi Baron
Thanks for explanation and for that link!
I tried with KHexEdit and i saw that value and with an amsn video cam i got 0000

Bye

[Kreuger]

@Kreuger: the quality of the image is dependant on the webcam, the quality of the *encoded* image is dependent on the codec used (the one used by msn is mimic and it has a configurable quality for the encoding), and the framerate is dependent on the internet connection.

Makes sense but seeing as I've never done it I wouldn't know otherwise . Now I do