Agg...what's happening to my mpeg4 render?

goshep wrote on 2/14/2008, 10:09 PM
I'm trying to render some recently captured dv footage. The total time of the footage is 39 minutes and the combined file size (before render) is 7.63 GB. I'm trying to render a quicktime file to be served to the PS3. The render settings were the Quicktime default (uncompressed). The render time was a little over 2 hours on a quadcore with 4 gigs of ram and RAID 0. The resultant file is 83.6 GB!!??

What the heck am I doing wrong? I've never seen anything like this before and I can't remember the last time my quadie couldn't render a project in at least close to realtime.

I forgot to mention....all four cores never seemed to go above 20% during the render. Never seen THAT before either. This is the first SD work I've done since upgrading to 8.

Comments

goshep wrote on 2/15/2008, 5:22 AM
Sorry for the bump but I know many of you are waking up and hitting the keyboard now.
rs170a wrote on 2/15/2008, 6:08 AM
That sounds about right.
I just tried rendering a 4 1/2 min. SD AVI to uncompressed QT on my Q6700.
Render time was 17:30 and file size was 10.3 GB.
CPU usage ranged from 7% - 14%.

Mike
winrockpost wrote on 2/15/2008, 6:31 AM
im no mpeg4 guru, but seems to me the uncompressed setting is just that.... not mpeg4 but uncompressed... why not use the export to psp option ?
johnmeyer wrote on 2/15/2008, 8:18 AM
Uncompressed will always be the same (HUGE) size, regardless of the codec used because, not to be funny, because there is no compression!!. And because of the whopping size, it takes longer (just to copy it to the disk drive).
goshep wrote on 2/15/2008, 9:10 AM
Will export to PSP create an acceptable file for PS3 as well? I love that ugly black contraption but it sure is finicky about codecs.

Johnmeyer,
This begs the question (and it may be another dumb question); why did the file size increase 80x? Isn't the raw DV footage also uncompressed? UNcompressed I can get my head around but the resultant file appeared to be DEcompressed and even inflated. Perhaps I'm still overlooking the obvious. In the meantime, I'm gonna try out that export feature. Thanks as always for the responses.

johnmeyer wrote on 2/15/2008, 10:01 AM
This begs the question (and it may be another dumb question); why did the file size increase 80x? Isn't the raw DV footage also uncompressed?

No, DV IS compressed.

This is a common misperception, caused by the fact that when rendering to MPEG-2 for DVD, an hour of video that originally took 13.5 gigabytes per hour (DV size) now fits onto a 4.7 gigabyte DVD.

DV compresses each frame using the same type of compression used for JPEG still photos. Each frame is compressed without any reference to frame that preceded it, or those that follow. Without this compression, an hour of SD NTSC video requires about 64 gigabytes; with DV compression, that same video only requires 13.5 gigabytes.

By contrast, MPEG-2 (and HDV high-def video) compresses an initial frame in the same way as DV video, but then compresses the next "n" frames by storing only small "difference vectors" that describe what has changed since the initial frame. This lets the video be stored in a much smaller space, but results in far more artifacts, and also makes it very difficult (although not impossible) to edit the video with any speed because the editing program (e.g., Vegas) must internally keep a dozen or more frames in memory at any given point in time, just to display one single frame of video. To do this well (quickly) requires a programmer who really understands the concept of "data structures," something taught in every computer science class, but which only a few really good programmers ever really master.