Newbie Rendering Question

Rjs0905 wrote on 9/4/2008, 11:42 AM

I've got 114 minutes of 1920x1080, 60i, AVCHD video from my Canon HF100 and want to author a BDMV. Load it into Vegas Pro 8.0b, edit, and attempt to render using the Sony AVC template (1440x1080) with AC-3 5.1 sound. The render is painfully slow - about 2fps, which means a test-render of all 200,000 frames took about 30 hours. After complicating the project with more transitions, music, and titles, the AVC render just started crashing.

So I re-render the same project in Vegas with the BluRay MPEG-2 template (1920x1080, 60i, AC-3 5.1) and figure I'll just have to re-render it again back to AVC in Architect Pro 5. The render from AVCHD to MPEG-2 is much faster - about 10 fps - and goes without a hitch.

I put the rendered file - now M2v - into Architect Pro, create the BluRay, and use the 1920x1080, 60i, AVC BDMV template for the Project. I'm anticipating a very long wait to re-encode from MPEG-2 to AVC and burn the disc, but instead it only takes about 45 minutes to create the disc and it doesn't appear that it is re-encoding the original video at all. Total size of final BDMV is 23GB, burn to disc, plays fine, no problems. Stream files on the burned BDMV show as m2ts files.

It just seemed to me that my original workflow, from AVCHD to an AVC BDMV, would be quicker than going from AVCHD to MPEG-2 to AVC BDMV, but that was not the case. Aren't AVCHD files and AVC BDMV's pretty much the same thing, using the same codec?

Comments

JohnnyRoy wrote on 9/4/2008, 3:12 PM

Here's what you did:

Source = 1920x1080, 60i, AVCHD

Render AVC template = Sony AVC template (1440x1080)

You were asking Vegas to take every single frame of your video and convert it from 1920 to 1440. So every frame must be resized and the pixel aspect changed from 1.0000 to 1.3333.

Then you tryed:

Render MPEG-2 template = BluRay MPEG-2 template (1920x1080, 60i, AC-3 5.1)

And it went faster because you were encoding 1920 to 1920 so only the encoding was different.

What I don't understand is why you didn't just use the MPEG file on the Blu-ray? I encode all of my Blu-ray discs using MPEG-2.

~jr

Rjs0905 wrote on 9/5/2008, 5:41 AM

Got it - That makes sense. Thank you.

I was trying AVC because I wanted it all on a 25G BD-R, and my understanding was that AVC compression yields smaller BDMV sizes as opposed to MPEG-2. My guesstimate was that encoding this to MPEG-2 would have given me about 32GB on the BDMV, too big to fit on a single layer, and the BD-R DL's are too darn expensive.

John_Cline wrote on 9/5/2008, 10:47 AM

Whether it's AVC or MPEG2, the ONLY parameter that determines final filesize is the bitrate. AVC and MPEG2 at 20Mbps, for example, would result in exactly the same size file. The advantage to AVC is that it looks better than MPEG2 at lower bitrates.

You can easily get 114 minutes of video on a Blu-ray disc if you encode it at at 27,000,000 bps and use 192kbps .AC3 audio. In fact, you could use 48k 16bit linear PCM audio and encode the video at 26,000,000 bps and still make it fit. At these bitrates, there isn't going to be much (if any) difference in quality between MPEG2 and AVC, however, encoding to MPEG2 is going to be a LOT faster.