Smart rendering AVCHD in Vegas Pro 9c

PeterDuke wrote on 9/23/2010, 7:47 AM
After some experimentation with VideoReDo 4, which does frame accurate trimming of AVCHD, and AVS Video ReMaker, which only cuts at I-Frames, but otherwise no significant re-rendering in either, I have come to the following conclusion:

In order for Vegas 9c to smart render an AVCHD clip, the clip must have all GOPs with the same number of frames. If you trim an AVCHD clip you should only do it at I-Frames. (There are, no doubt, other necessary conditions as well.)

Does anyone have any evidence to the contrary?

The clips produced by my Sony camera seem to only have 13-frame GOPs in them (25 fps PAL).

Clips trimmed with AVS Video ReMaker will smart render in Vegas 9c, but unfortunately that program only gives you the options of stereo (not 5.1) LPCM or none for audio output.

Comments

Laurence wrote on 9/23/2010, 8:33 AM
That's how it used to be with mpeg2 smart-rendering programs like Womble Mpeg Wizard as well. Then they evolved to the point where they could edit anywhere by messing with the iframe sequence. The resulting mpeg2 smart-renders would play back on DVD players just fine, but if you looked at them closely, you could see a very unstandard iframe sequence.

Vegas does this as well when it smart-renders mpeg2. Unfortunately this means that the editor has to buffer back to the iframes on each clip. For a while this was evident in that you could only put a certain number of mpeg2 clips (hdv clips) on a Vegas timeline before it would crash and become unresponsive (less than 100). Sony supposedly fixed this a while ago, but I still notice that while that number is a lot bigger now, Vegas will still crash if you put too many mpeg2 clips on a timeline at once.

Anyway, what you are seeing is a similar evolution with AVCHD. Now Video Redo will smart-render AVCHD, but only at the iframes. I imagine that soon Womble will be doing that as well. After a while, these programs will be modified to write iframes anywhere. Vegas will eventually smart-render AVCHD as well. Then people will notice that you can only put so many AVCHD clips on a timeline at once before it crashes. Then that number will be raised so that the majority of people don't complain.

IMHO, it is easier to just use an intermediate like Cineform or MXF. That or on small projects you can use DVFilm Epic. Smart-rendering is useful for some things like home movies or folding sections into a larger piece, but it has limited use in productions with niceties like color correction and titles, and the unstandard iframe and GOP sequence is a problem that can't be fixed.
PeterDuke wrote on 9/23/2010, 5:37 PM
Yes it depends on how much colour correction, stabilization, text subtitles, transitions, etc you plan to do as to whether it is worth struggling to get smart rendering or not.

Since my first post I have been pondering on some anomalies in my experimental results and it may not be quite as simple as I suggested. Are there such things as padded GOPs where a final GOP is not completely filled?

A point of clarification to Laurence's post: VideoReDo 4 will smart render AVCHD with trimming at any frame, not only I-Frames. That means that only the video between the cut and the nearest I-frame is re-encoded. The rest is just copied.

AVS Video Remaker will only trim AVCHD at I-Frames, and does no re-encoding.