So you are trying to play back 4 streams of 1920x1080 ProRes 422 (HQ) in realtime from a single 7200rpm FW800 drive? Seems to me your issue is not with RAM, its with your storage, its not even close to what you need for what you are editing. Why are you using ProRes 422 (HQ)? That'll set you back about 220 Mbps per stream, 880 Mbps for all 4 streams, and your FW800 drive is only theoretically able to offer 800 Mbps (in reality it'll be less). What kind of content is this? If its a multicam edit then I'm guessing its not green-screen work. What is the original source footage format. If its H264 then you sure as **** don't need to be transcoding to ProRes (HQ), thats a mugs game. Chances are you would be just as pleased with the visual quality of ProRes 422 (LT), unable to spot the difference ... and it would be far more suitable for your editing setup's capabilities.
Hope it helps
Thanks man! It's quite clear.
Yup, the footage were AVCHD.
How much different of "Mbps" in between ProRes (LT) vs ProRes (HQ)? What about just go for ProRes without HQ or LT? Will makes playback smoother in real-time?
For the AVCHD footage, what's the best codec for Editing? I'm wondering that seems ProRes only provided a huge file instead of better quality for footages are only AVCHD which is the Max Quality, how do you say?
ProRes HQ runs at 220 Mbps vs. 102 Mbps for ProRes LT. For AVCHD footage you are not going to gain anything by going HQ. You can see a chart here that shows the various flavors of ProRes.
To understand why ProRes gives you a bigger file than AVCHD you have to understand different compression schemes. Basically, AVCHD only saves information for things that change between frames, where ProRes saves all the information for each individual frame. That is a gross over simplification but you get the idea hopefully.
Anyway, for AVCHD just use ProRes LT and you will be fine.
You could go with plain vanilla ProRes ... that clocks in at around 145 Mbps ( almost 600 Mbps for 4 streams ) but seriously, if you started with AVCHD then you really don't need to use more that ProRes (LT) which will run you around 100 Mbps per stream. Neither you nor your viewers will be able to tell the difference, and the whole edit process will be much smoother given the specs of your system.
Heres a handy description of the ProRes family:
Here's a quote from forum reguar Red Truck who sums it up quite nicely:
If your footage was shot in AVC or an MPEG2 codec (like HDV or XDCAM) at a bit rate of 35Mb/s or less, use ProRes LT. If your footage was shot above 35Mb/s (e.g. 5D @ 44Mb/s) then use standard ProRes 422. If your footage was shot in 2k or above, and you're downrezzing to 1080, use ProRes HQ.
If your original source is AVCHD then I recommend that you transcode it to ProRes (LT) when you ingest (you can do this using Log and Transfer) ... then you work using ProRes (LT) as your edit format.
H264? Heck no. That is NOT a suitable intermediate. If you had H264 source files then I would be recommending you transcode those to ProRes (LT) too. AIC is an alternative intermediate codec you could use instead of ProRes (LT), but the latter would be the more preferred option.