Recompression issues

Jack S wrote on 6/11/2011, 8:31 AM

I wonder if anyone can help me with this observation.
I've just started editing clips taken with my new Sony HDR-XR550VE camcorder. I created a rendering template based on clip information provided by MediaInfo. Rendering worked fine with only the transitions, titles, effects, etc. being rendered and no recompression carried out on the remainder (shown by the words 'No Recompression Required' shown in the preview window).
If I then bring the file created above back onto the timeline and use the same rendering template it looks as if the transitions get rendered again. I would have thought that since the whole file conforms to the rendering template none of it would be recompressed.
Just to explain why I would need to do this. My normal workflow consists of editing single events (birthday party, day trips, etc), creating the individual segments then bringing all the segments onto the timeline to produce the final MPEG file.
It's not a big issue because it looks as if only the transitions are being recompressed but I was just curious why this should happen.
By the way, this didn't happen when I was working with AVI files imported from my old DV tape camcorder.

Comments

Eugenia wrote on 6/11/2011, 10:21 AM

Are you exporting as HDV? You don't provide this crucial information.

Jack S wrote on 6/11/2011, 11:36 AM

My apologies. No, I'm working with SD clips and exporting at the same bit rate, etc. so no recompression on the clips themselves, just on the titles, transitions, etc.
My query was about bringing the exported file back onto the timeline and exporting it again using the same rendering template. Theoretically, VMS shouldn't need to recompress because there's no need to. However, although the titles don't recompress (which is what I expected) the transitions do (or so it seems from what is shown on the preview window).

Eugenia wrote on 6/11/2011, 12:41 PM

No, Vegas only smart renders DV AVI and HDV formats. If that's not how you're exporting, then it won't smart render. Again, you need to tell us both the actual input format used (vegas can tell you in its properties of a clip), and exactly how you export.

If both are DV AVI, then my guess would be that Vegas fails to read properly the aspect ratio or field order of the exported DV AVI, and so when you import that the second time over, the project properties are supposedly mismatched to the file, and so it refuses to smart render. The AVI container has no proper attributes for field order and aspect ratio you see, it's a very old format and reading these properly is pretty difficult. I had field order/aspect ratio problems with other AVI formats and that was Sony's response.

Jack S wrote on 6/11/2011, 2:29 PM

The input format is
MPEG-2, 720x576x32, 25fps (PAL), Upper field first, 1.4568 pixel aspect ratio (PAL DV Widescreen)
The output format is the same.
You say that Vegas only smart renders DV AVI and HDV formats but the format I'm using (MainConcept MPEG-2) does smart render. Only the titles, transitions, etc. are rendered.
My question was, why should Vegas recompress the parts of an exported file brought back onto the timeline, that it recompressed during the export. The original exported file should be compatable with the original template used, therefore no recompression should be needed.
It is possible though that the mechanism is far more complex than I think it is. If this is the case then I will accept the facts and close this thread.

Eugenia wrote on 6/11/2011, 2:56 PM

I guess it's obvious that the exporting mpeg2 format from MainConcept is not as Vegas expects mpeg2 to be, and so it recompresses it. If when selecting that template the "custom" button is enabled, you can try out things in that dialog that might make vegas "like" the resulted mpeg2 file more and not recompress it.