Why is Vegas so wimpy with its prerendered video files?

jeremyk wrote on 9/19/2003, 4:32 PM
I did my 4-hour prerender so I could do a final check on my various titles, composites, etc., before printing to tape for the REAL final check on the living room couch. I watched the video carefully to find problems. When I found them, I carefully made note of them without touching anything, because of what I've learned through experience:

Vegas is VERY quick to toss overboard perfectly good prerendered video. All I changed was some compositing clips, without changing the timeline position of anything, and all the prerendering is GONE.

I haven't yet figured out what algorithm it's using, but it would seem to be pretty dumb. Even prerendered files preceding the part I'm changing get thrown away, so that lets out the strategy of making changes starting at the end and working backwards. And rendering takes SO LONG.

How do other folks use this thing?

Comments

johnmeyer wrote on 9/19/2003, 4:44 PM
I have had the same experience. It is one of the few areas where Pinnacle does a much better job. Hopefully Sofo/Sony will correct this in the next release. It would save lots of time.

Having said that, it will be difficult to figure out what hasn't changed. When you have hundreds of events and dozens of tracks, thre would have to be some pretty clever algorithms tracking every aspect of every event to know what had or hadn't changed. It should be doable, but it won't be easy ...
GaryKleiner wrote on 9/19/2003, 4:47 PM
A method that will work better for you would be to Render To New Track, so it would be more under your control.

If you need to make a change, just cut a hole out of that section of the rendered media and make the changes below.

Gary
r56 wrote on 9/19/2003, 5:02 PM
For small segments I use the Dynamic Ram Preview, for longer and complex segments that I need to watch in real time during editing, I render to a new track. I rarely use pre-rendering during editing because the files won't last a bit. First of all with every ripple edit (affect all tracks mode) all rendered files get useless even if the performed edit doesn't affect anything on the timeline. I am also curious whether other people find it annoying or are used to.
pb wrote on 9/19/2003, 10:51 PM
That suggestion about rndering to a new track then putting replacement clips above the affected areas is the best solution. I use the RAM preview because of the Selective prerender evaporation issue, really pissed me off the first time the little green blocks disappeared.
rmack350 wrote on 9/20/2003, 2:09 AM
The dissappearing prerenders are a big drag but if you've done the prerender its a pretty quick job to then render to a new track. And if you see the prerenders disappear you can undo and then render to new track. Usually vegas is just writting the prerenders to a file and putting it on the new track.

But you can skip the step and just make the new track right from the start.

One of the things I've imagined that nested clips and sequences would do would be to make the prerenders stick. You take a range and collapse it to a nested clip and then vegas would prerender in the background and keep it until you open the clip and change it. It would be a lot like rendering to a new track but without new tracks.

Rob Mack
Brazilian wrote on 9/20/2003, 1:14 PM
> When you have hundreds of events and dozens of tracks,
> thre would have to be some pretty clever algorithms tracking
> every aspect of every event to know what had or hadn't
> changed. It should be doable, but it won't be easy ...

Easier than you might think. One way I could think would be to take each clip and calculate a checksum, like an md5 sum, based on as many unique properties of the clip as possible: It's name, timecode range, and parameters of the effects. You can then keep a table of these md5sums and very quickly compare them against a list of md5sums of the prerendered clips to tell if something had changed or not.

The AVID DS for instance is hyper-intelligent about this sort of thing. It will break renders down into multiple segments anytime there is a cut on any track, so most of the time when you change something, it ONLY has to re-render the exact frames affected... even if the change was moving 1 keyframe, it only processes the frames affected by the change. And it keeps these prerenders around until you ask it to purge them (they call them caches) so if 5 minutes later you hit Undo a bunch of times and your keyframes go back to the way they were, DS will link back to the original render it already had that matched those settings.

This method also allows it to see multiple clips on the timeline that are the same, and only render one cache and share it between the common sections.