ATI's Best: All-in-Wonder Radeon 8500 128MB & TV/Capture Card Roundup

Time Shifting

Thankfully the software supports time shifting which is the ability to encode a TV stream while watching it. This brings about the concept of pausing live TV much like you're probably used to seeing from set top boxes like those made by Tivo and Replay. When time shifting is enabled the video encoder chip on the card begins capturing the video that you are watching to your hard disk, you can then rewind to see something you missed and it will continue to record the video. Then after you're done you can return to where you left off or fast forward to live TV. This even allows you to hit the pause button to go to the bathroom or answer the door and return to your favorite show.

Time shifting is a very intensive scenario for a piece of hardware to be placed in as it must be able to encode (by today's standards, MPEG2 encoding should be used) and play back a video stream at the same time. Depending on the size and quality of the video being encoded CPU utilization can range between 10 - 100% while time shifting. Factors that come into play here are support for iDCT and motion compensation in the graphics hardware (which help free up the CPU quite a bit). Unfortunately for Matrox, the G450 does not support either feature and thus the task of time shifting falls entirely on the host CPU.

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On our Athlon XP 1900+ test system the CPU utilization seen while time shifting at 352 x 240 in SP mode (1.02MB/s) was between 20 - 40%. Interestingly enough, the utilization did not increase noticeably when we started time shifting at 720x480.

A unique feature of the PC-VCR software is the ability to run Picture-in-Picture mode with the time shifted material in one picture and the live material in the other. Remember that since there is only a single tuner present on board you can't record a channel you're not tuned to.

In terms of actually channel surfing and watching TV on the card, the G450 eTV does a relatively good job. Switching channels takes a noticeable delay but the tuner is still quicker than the one in NVIDIA's Personal Cinema which you will read about next. A major annoyance is that as soon as you enable time shifting there is a 5 second delay between when you hit the button and when the program actually starts recording, so you have to anticipate when you want to begin recording so you don't miss any of your show.