Video Capture Considerations

Capturing video with your TV/Capture card requires a great deal of system resources. The larger the image you try to capture the more resources that are required and the larger the amount of data that needs to be moved. Every time you double the size of the image you quadruple (2 squared) the number of pixels and data that need to be transferred. When you change from 16-bit color (2 bytes) to 32-bit color (4 bytes) you double the amount of data needed. So, if you double the size and the color you are getting 8 times the data needed to be transferred.

Please refer to the chart below indicating the limitations imposed by hard disk drives on capturing video.

 

Data transfer Rate in Megabytes per second for given color, size and frame rate.

 

Format

Bits Per Pixel

Resolution

Frames/second

MB/Second*

YUV-9

9

160x120

15

0.324

YUV-9

9

160x120

30

0.648

YUV-9

9

320x240

15

1.296

YUV-9

9

320x240

30

2.592

YUV-9

9

640x480

15

5.084

YUV-9

9

640x480

30

10.368

RGB-16

16

160x120

15

0.576

RGB-16

16

160x120

30

1.152

RGB-16

16

320x240

15

2.304

#RGB-16

16

320x240

30

4.608

RGB-16

16

640x480

15

9.216

RGB-16

16

640x480

30

18.432

RGB-24

24

160x120

15

0.864

RGB-24

24

160x120

30

1.728

RGB-24

24

320x240

15

3.456

RGB-24

24

320x240

30

6.912

RGB-24

24

640x480

15

13.824

RGB-24

24

640x480

30

27.648

 

 

IMPORTANT NOTES:

                    SCSI drives transfer date at a rate of about 18 megabytes per second 

 

# Indicates the practical limit in most computers. Note that 320x240 at 16-bit color and 30 fps, while falling within the specification for data transfer, may not capture a full 30 fps. This is because the computer must also capture sound.

 

 

Setting up for video capture.

After having reviewed the information above please consider the steps below before setting up your configuration when doing a video capture.  

  1. Make your capture size as small as possible (see settings window below)
  2. Keep your color depth as low a possible (16 bit is lowest for the TV card)
  3. Set your frame rate as low as you can tolerate (see settings window below)
  4. Turn off sound capture or set Windows for the lowest quality sound this setting is part of the Multimedia properties in Windows 98 set the Sample Rate Conversion Quality at Good in Windows 95 set the Preferred Quality to Radio Quality.
  5. Make sure NO other programs are running in Windows when you are trying to do a video capture.
  6. Start at the lowest possible settings for all parameters and work up toward your desired result.

 

Capturing video requires most of your system resources and capabilities. Using as few of these resources as possible allows you to capture more frames per second. The bottleneck, as shown in the chart above is that of the hard drive data rate. Capturing sound also requires a great deal of system resources this is why we want to keep the sound quality as low as possible.

The computer system itself and the settings in the BIOS have a great deal to do with how fast your system is able to capture video. The video card and the amount of memory on that card also have an affect on your capture capabilities.

 

Inability to Capture

The two main reasons for not being able to capture video are:

  1. An IRQ conflict (please refer to separate document on resolving IRQ conflicts)
  2. Having a conflicting Video Capture Device
    1. You can Remove the device completely or
    2. Click Do not map through this device and Do not use this device to disable this driver this method is supposed to allow you to switch back and forth between different capture drivers.
    3. Open Video Compression Codecs (see list in graphics above).

The graphic below shows several standard Codecs installed in Windows 98. Having Codecs listed here that you do not recognize can be an indication that you had (or have) another capture device installed on your system that did not get fully uninstalled. Do NOT arbitrarily remove any of the Codecs on your system. The Codecs do NOT cause any trouble. They are merely indicators that you have something installed on your system that may be causing you a problem with capturing.