Even though the RealCap software module is simple and easy to use many thing can go wrong in the capture process. To give you a better understanding of capturing video this small guide will explanation about the various aspects of the capturing process. Maybe this could solve the problem you might experience.
One of the most
important issues in real-time video capturing is whether the PC system is capable of
storing the amount of data onto the hard drive. In full size and full speed (NTSC mode)
the amount of data that has to be streamed onto the harddrive is approximately 27Mb (24bit
color * 720 * 480 * 30 frames/sec). This amount of data can only be streamed onto a hard
drive using very expensive equipment. Not only the hard drive must be very fast but
also the data bus on the mainboard. I know that today's PCI bus and hard drives with Ultra
DMA are capable of data transfer of up to 33Mb/sec of data throughput. But it must be
remembered that this is in extreme cases where the system does not interfere on the bus,
which is hardly the case for any Windows operating system. The real throughput on these
system (in situation where the system has been optimized) is about 8-9Mb/sec which is
still allot. In order to stream the video data onto the hard drive the amount of data must
be reduced. In our system the reduction is done using Motion JPEG format. There is also
the MPEG standard but unfortunately the equipment for full speed and size video capturing
is still too expensive.
When displaying the
video data on the monitor there are two options that can do the trick. First option is
called preview mode, which means that the computer forcibly extracts a
video image from the video stream each .5 sec and renders the image on the screen/monitor.
This is off course time consuming because the processor is part of the whole process. Also
when searching on the video it is not always easy to find the location from where you want
to capture using only 2 images/sec. Most current technologies utilize this mode which is
not accepted in real time video capturing unless you do not have another choice. The
second option is called overlay mode and it is a special no processor
depended operation, where the capture card is capable of streaming the video data directly
to the display card memory. This is a very powerful option and leaves allot of idle
processor time for other programs and the current running application - The RealCap.
After the video has been captured it is unlikely that the start position of the captured video will mach any other captured video sequence from another angle/view. In 3D biomechanical analysis it is required to use more than 2 view in order to transform image coordinates to spatial coordinates. Even if taking advantage of VCR synchronization the VCR mechanism will not always respond with the same time delay. This means that the start position will have to be modified/trimmed in order for them to correspond. After the video sequence has been captured the RealCap proceeds directly to a trimming process which enables you to modify the video sequence, selecting a synchronization image and the amount of pre and post images.
For more Video Essentials with the APAS please click heere.
In the following are more resources of information about Video and Video drivers utilized in the APAS System. However, the only thing you need is to install the software as described above. You do not need to understand it, but I reccomend it so you know what is going on. The following driver is needed for computers that cannot have the Buz card, such as a notebook. You may want to be able to digitize and sychronize video sequences that were captured on the desk top, with your Notebook sitting on the beach, or on airplan. Or, maybe on the weekend at your home. (don't tell your wife, I suggest that....). Or let your students work at home. Why would you want them around you all the time... I am doing this allot... For that reason, you must have a MJPEG drivers to be able to see the video on your notebook.
The MJPEG-Software-Codec Guide
About the Morgan Multimedia and Paradigm Matrix M-JPEG codecs
What on earth is a codec ?
The compression is done during capturing in realtime by a Zoran-chip on the RR. Your
captured video file contains an identifier (called FourCC) in its header that shows the
subformat. For Matrox-MJPEG the identifier tag is "dmb1". If you open a avi
file, the Video-for-Windows routines examine the avi file header and read this identifier
tag at first.
Interesting excursion: If you disable the VIDC.dmb1 setting by inserting a semicolon before its entry in the system.ini, the video-editing software will still be able to handle avi-files with the dmb1-tag, and both the ActiveMovie-Player and the Matrox PC-VCR software can play and output those files ! We even can record avis with the PC-VCR and other capture programs without the system.ini entry.
OK, let us draw some conclusions. Whenever we record a MJPEG-avi file with the RR it
contains the dmb1 tag independent of any system.ini settings.
Why should I use another codec ?
The Morgan- and the Paradigm-codec produce MJPEG-avi files (with a
higher quality and certainly higher data-rate if you want). If your system is fast enough,
you can improve the quality of your videos and reduce artefacts. Some actions are faster
with those codecs and some not...
There are two groups of RR-users who should use one of the software
codecs. Windows NT users and users of a Millennium II+RR having trouble with the
"snowy-frames" problem. Windows NT users suffer from the NT-drivers lack of
MJPEG-support. With the software-codecs they get the possibility to process and playback
their MJPEG-videos in NT. They still have to record the MJPEG-videos with Windows 9x.
You can replace the Matrox-codec by the Morgan-codec (recommended method)
You must make the following changes to the system.ini:
The drivers "user FourCC"-field must be enabled and set to "dmb1". After that you can work with your RR like before but without "snowy-frames" and with better quality ("Integer" or "Float" method for "Compression" in Morgan codec settings and "Higher Quality" in Paradigm codec settings) . You dont have to patch any avi-files. Avi-files played with ActiveMovie, Matrox PC-VCR or MSP5 (best Preview) make use of the RRs hardware-accelleration and can be recorded on tape etc.
You can replace the Matrox-codec by the Paradigm-codec
You must make the following changes to the system.ini:
And you must make an additional entry to the registry with regedit:
Path: HKEY_CURRENT_USER\Software\Paradigm Matrix\Software M-JPEG
64=d 6d=m 62=b 31=1 => 31626d64=dmb1
The Matrox-codec is disabled and the Paradigm-codec is made responsible for all
avi-files with the Matrox dmb1 identifier tag.
You can use the Morgan- and the Paradigm-codecs as additional codecs
Your system.ini entries must look like the following:
This value stands for 'dmb2' ! Don't confuse with 31626d64 for 'dmb1' !!!
The Morgans "user FourCC"-field has to be disabled or if you like to enable it set it to "MJPG". If you use avi.exe you must change the content of the Morgan-button from "mjpg" to "MJPG". "mjpg" was used in earlier driver versions but it has changed to "MJPG" because of the specs.
All codecs are active and can be used to decompress and compress
avi-files. You can define which codec will be used for which file by changing the
identifier tag in the file header of each file. If you want the avi to be decoded by the
Matrox-codec the identifier tag must be "dmb1". If you want it to be
decompressed by the Paradigm-codec the id-tag must be "dmb2" and
"MJPG" for the Morgan-codec. You should use the avi.exe Windows program to
change the identifier.
General info about using the other codecs
You must keep in mind that the MJPEG format is a compression format.
MJPEG stands for Motion JPEG. I guess all of us have used pictures in the JPEG (.JPG)
format. The file size is very small after converting a tiff (uncompressed) to JPG and the
quality is decreased. The more you compress the less is the quality.
If you want to increase the quality of your captured videos you can
try to use Doc Mordrids overclocking method, which is described at TIGRR. If you are not familiar with
editing the registry you can use the tool MJPG.EXE to change the registry-settings.
Morgan Multimedia M-JPEG codec
Last edited 19.11.1998 by Uwe Roeder.
The above information is a detail description of installing different video drivers. The APAS system in most cases doing it for you automatically. The only time when you have to install these drivers is when you do not have the capture card installed on your computer. In this case you can digitize and analyze the data but you cannot capture. Obviously, you cannot capture without a capture card. But you can analyze data that was capture with another computer capture card. These allow a situation in a classroom, for example, where there is one master system with a capture card and all the students have only the drivers to analyze the results. That means, that you do not need to purchase more then one APAS system. You purchase one, and use it on as many as you want. This is one of the uniqueness of the APAS and one of the most important factor to consider when purchasing any Biomechanical System.
Tips For Better Capture