Thanks to MPEG compression, we might not have as big a problem as first appears. With MPEG compression, video camera does not have to send entire image for every frame. It sends only data for part of image that changed, and it compresses that part.

If image doesn't change much, and part that changed compresses well, video camera might need to transfer at a rate of only a few MBps. But if entire image changes every frame and image does not compress well, video camera might transfer data at a higher rate than computer monitor is capable of displaying.

Again, we have two devices that operate at different transfer rates that must communicate. We can make them work together by placing a buffer between them. When you start recording video, video recorder starts filing buffer. The computer display immediately begins pulling data out of buffer to compose display frames.

If everything goes smoothly, computer display will be pulling data out of buffer fast enough so that buffer never completely fills. If buffer fills up, video camera can't put any more data in, so it stops. Buffer overrun error.

We can reduce chances of buffer overrun by defining a larger buffer. Then video camera will be able to put more bytes in bucket before it fills up. Hopefully, video camera will run into a few frames where entire image doesn't change, reducing its data transfer rate enough so computer display can catch up.

Underrun, Overrun Protection

Today, CD recorder buffer underrun is much less common. Computers come with much more RAM than they did before, and CD recorders have learned to monitor buffer and reduce recording speed if buffer starts to run low.

Video camera buffer overrun is also less common. Video uses a program called a "codec" (for encode/decode). A smart codec can monitor buffer and reconfigure itself when buffer gets too full. It might for example automatically reduce color depth of video, or drop frames, until computer display catches up.

Underrun and overrun Protection doesn't completely solve problem. If underrun protection activates, a CD recording session will take much longer. If overrun protection activates, video quality will be reduced. The only way to solve underrun and overrun problems, after increasing size of buffer, is to match data transfer rates of devices that need to communicate. You can upgrade to a faster hard drive, or install to a high performance video card.

Now, if you need to troubleshoot a buffer underrun or buffer overrun errors, at least you know what a buffer is, why we need buffers, and what causes buffer underrun and buffer overrun errors.

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