I have finally succeeded in creating a usable Tivo replacement using the ATI AIW Radeon and ATI's MMC 7.1 software with the Gemstar TV guide. The major problem was surmounting the famous (infamous?) dropped frames problem that numerous board members (including me) have been experiencing with the ATI MPEG encoder used with the ATI MMC. After much searching through various forums including this one, I decided on the following equipment:
Motherboard: ASUS P4T
CPU: Intel P4 1.5Ghz
Memory: 256 PC800 RIMM
Video: ATI AIW Radeon (3102 driver)
Sound: Creative Soundblaster X-Gamer
Storage: IBM 75GXP 75gig hard drive
OS: Win2k SP2
With this "power" setup I am able to do MPEG capture at 720x480, IBP frames, 10Mbit/s, full motion estimation(99), full motion search settings (256 horizontal, 128 vertical) with NO dropped frames!!!. I've done no tweaking whatsoever to achieve this result, just standard installs of all of the software. CPU utilization is at around 75% during capture.
For the justification for this setup I used the following factors which affect MPEG capture:
1) MPEG encoder settings. Seems obvious but the higher the parameter settings are pushed, the more likely you are to exceed your computer's resources thus resulting in dropped frames. However my requirement was that I should be able to max out all settings and still have no dropped frames. Therefore this wasn't a factor I was willing to compromise on. For my purposes I wanted to be able to support MPEG capture settings of 720x480, IBP frames, 8-10 Mbit data rate, full motion estimation(99), full motion estimation search ranges (256 horizontal, 128 vertical), CD quality sound. Pretty tall order, eh?
2) CPU power. Another obvious one. Better MPEG2 capture requires more horsepower. For my settings it appeared I needed at least a 1 - 1.2 Ghz CPU to handle the load based on the empirical data I was able to gather from the experiences of others. Just to be safe I decided to get 1.5Ghz to give myself a little headroom.
3) RAM bandwidth. No matter how fast the CPU is, if the memory bandwidth cannot handle the enormous amounts of data being shuttled through it for the motion estimation calculations then dropped frames will result. Regular SDRAM doesn't seem to cut it. DDR might but I didn't want to take any chances so I chose Rambus which supports a 3.2gig/s transfer rate (theoretical)
4) Disk speed. Actually this doesn't seem to matter that much. It appears that pretty much any ATA66 and above drives can handle the load. MPEG in general doesn't produce the gobs of data that AVIs generate so most drives have no problem keeping up.
5) OS. Yes the OS does appear to make a difference. Using a similar setup to my hardware above, I installed a friend's computer with win98 instead of win2k and he got dropped frames!!! (astonishing given the P4 1.5Ghz and the Rambus memory!!). Therefore win2k seems to be a better OS for video capture than win98. I must mention that my friend had 128mb of memory instead of my 256mb but given that I never noticed memory consumption above 90mb on my machine I dismissed this as a factor.
Make sure that you install SP2 if you're going to be doing video capture with ATIs MMC. I was having intermittent crashing problems until I installed SP2.
Win2k breaks the 4gb barrier (if you install NTFS) allowing video capture up to the available space of your hard drive. No need to worry about capturing those long movies anymore.
In addition to excellent video capture, the Tivo functionality of the MMC works very well in my setup. I can pause and rewind Live TV without any of the intermittent crashes I was experiencing under win98
Here's something wierd...Win2k reports my video, sound and network cards to be all on IRQ9 yet this has had no effect on my capture. This calls into question the conventional wisdom of having cards on separate IRQs?
Well, its back to having fun with my setup!
"The shortest answer is doing"
English Proverb. Collected in: George Herbert, Jacula Prudentum (1651).