Dynamic Ram Preview (The hows and why's)

Cosmerki wrote on 6/8/2002, 4:32 AM
I am building a 2.2+ Ghz Athlon system later this month and want to know exactly how dynamic RAM preview works so I can make an educated decision on an additional 512MB of RAM or no.

Does VV3 background render transitions and filters, effects, ect. while you are working on the timeline in anticipation that you will require a realtime preview of those difficult areas or does the processing to RAM only begin when you select a segment to preview?

If the second statement above is true then is it safe to say the ony real performance benefit to be gained by rendering previews to ram is the elimination of the processor overhead of going to and from the hard drive?

It appears from past posts that the RAM cache for previews fills after so many seconds and the fun is done. Why not make it like a FIFO buffer and "loop" while viewing, erasing the first frames viewed and filling them with ones to come. In this way a 200 or 300MB buffer and a fast processor could give the performance advantage of an unlimited ram buffer?

O' how I miss the days we had true pre-emptive multitasking. Adios Amiga!!

I may be way off base here, since I have no experience with VV3 yet. Please, if anyone can illuminate me I would appreciate it. THANKS

Comments

SonyDennis wrote on 6/8/2002, 9:58 AM
VV3 does not do background speculative rendering during idle time. However, as you move around the timeline, any frame rendered gets stored in the Dynamic RAM Preview storage, so if you go back there, there's a chance that it can just pull that frame out and show it, instead of going back and rendering. I say a chance, because, as you move through the timeline, it needs to remove frames in order to store the new ones. The algorithm for doing this is more sophisticated than a FIFO, it takes into account how far away the frame is, and how "old" it is, assuming you are more likely to want frames near where you've recently been.

Shift+B is a shortcut to say "I really want this consecutive range of time in the RAM buffer", so it steps through all those frames. It will stop before throwing out any of them, so this is why when you exhaust your RAM size with Shift+B, the time selection is cut short. It's holding as many frames as it can; if it created any new ones, another would have to go to make room.

///d@

P.S. Windows *is* preemptive multitasking. The PC and Mac industry has finally, mostly caught up with the Amiga <g>.
Cosmerki wrote on 6/8/2002, 10:23 AM
SonicDennis,
Thanks for your reply.
Can you please clarify that the rendering to ram for a preview does not begin until you chose a segment and hit the preview button?

So while you are watching the simpler parts of the clip the more difficult filters and transitions ahead are rendering?

Even with a very fast processor will it choke if you have some difficult scenes to preview?
If you give it a few seconds to render to RAM?

Are the previews done in an AVI format of some type or are they actually DV? How many frames per second are they? Someone earlier said it only renders every other frame, is this true?

Thanks Dennis
SonyDennis wrote on 6/8/2002, 4:00 PM
No, it's caching frames *any* time you navigate or play. So, if you're playing a section in a loop, after a while, the frames will all be cached (if you have enough RAM). Shift+B is just a shortcut to step through all the frames in a time selection to make sure they're in RAM.

If you haven't RAM cached frames, as you play through a "difficult" part (heavy FX, transitions, multiple composited tracks etc.) Vegas will drop frames as needed to keep up with the play cursor. The RAM cache is not a disk format.

You might be thinking of the Shift+M "Selective Pre-Render" tool which let's you pick the disk file format, although for a DV project, you should use a DV/AVI file format, so that External Monitor can work in real time. No frames are skipped during this pre-render, although on a slower machine frames might be skipped during playback. Once you've pre-rendered a section, it will always play fast, independentally of RAM caching.

These are just two tools to help you get real time playback for complex parts of your timeline. Use them together as you work on a project.

Unlike some other NLE's, you don't *have* to pre-render to see your FX or transition settings, they appear as you adjust settings, in the Video Preview window or on your DV device (External Monitor). This saves a lot of time.

///d@
Caruso wrote on 6/9/2002, 5:54 AM
SonicDennis: You stated: Once you've pre-rendered a section, it will always play fast, independentally of RAM caching.

I am one who works on a slow 900mhz/128mbRAM machine. Most of the previewing I need in my projects involves only a single track (although I may be have three or four source tracks on the timeline) and simple FX (dissolves, slo-mo, fades, etc). I'm no expert on RAM, but, WinXP reports that the max I have available for dynamic RAM preview is a measly 16 MB, so, I don't use it.

However, my experience with pre-rendering would seem to indicate that pre-rendering a section only lasts until the timeline is modified by introduction of another FX anywhere on the timeline that would, itself, require prerendering to view in real time.

Am I correct on this, or am I doing something wrong? . . . or, did you mean that pre-rendered sections would always play back until the timeline is modified?

Also, does 16mb sound like the right number as a limit on the system I described? The number is coincidentally the same as amount of "video RAM" listed in the specifications for my machine, but, I thought we were talking system RAM here.

Sorry if I display ignorance in this area, but, would appreciate any further pointers.

Thanks.

Caruso
SonyDennis wrote on 6/9/2002, 10:55 AM
Caruso:

Correct, your understanding is correct. Pre-render do disappear when you make changes below them. They're mostly useful for "finished" sections or sections you want to see with full-motion that won't fit in the RAM cache. Technically, they don't completely disappear, you can pre-render, make a change, and if you undo, the pre-render comes back. This makes playing through pre- and post-change sections easier, you can keep both pre-renders

One of my machines is 800MHz/128MRAM, so I am familier with your work environment. 16MB is the default Dynamic RAM size, but I think you can crank it up to 64M. With half-size Video Preview you can get quite a few frames in there.

Even with an 800/128 machine, for the style projects you're working on, if you've got fast disks, the regular playback should keep up for most sections, and you can use the RAM cache and pre-renders where it doesn't.

///d@