rendering settings in Vegas for 30p video for BD authoring

[Enrique Orozco]

…. if you shoot 30p (like me), just use the Vegas BluRay 1080 60i template …and author with DVD architect…. you’ll get excellent results …

good luck

Enrique Orozco R.
iDEA DigitalVideoStudio

[John Rofrano]

At 1080 resolution, Blu-ray supports 60i, 50i, & 24p. As Enrique said, use the BluRay 1080 60i template and you should be fine.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[David Kotlaba]

Thank you. I tried it and it looks really nice. Do you think, since my camcorder gives me the option to shoot in 24p, that I should try it and keep the whole workflow in progressive? Will it make any difference in the quality on the BD?

[Dave Haynie]

You have to decide based on your content.

Blu-Ray doesn’t actually support 1080/30p, though since all modern televisions are progressive, encoding it as 1080/60i doesn’t really hurt anything… that’s definitely your best bet with 1080/30p source material.

Try 1080/24p, which is a Blu-ray supported format, and see if you like it. This is usually included for a film-like look (cinematic films are shot at 24p and shuttered at 48p or higher on playback). Good for low light, too (a 180-degree shutter look at 1/48 second rather than 1/60 second with 30p), but not so good for fast motion (I shoot sports at 720/60p, which is also a Blu-ray supported resolution).

-Dave

[John Rofrano]

You could shoot the whole thing in 24p but you need to learn how to shoot for 24p. You need to make very slow and deliberate movements. You can’t just swing the camera around like you can with 30p or 60i and get smooth video. I would try practicing on a picket fence. Perform slow horizontal pans across the fence until you can get them smooth without jerkiness. If you move the camera too fast, you will get jerky video and there is no fix. So practice your movements if you plan to shoot 24p.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Dave Haynie]

This is particularly critical if you’re using a modern HD video format on your camcorder, like MPEG-2 or AVC. And the care you need to apply, or the penalties for fast motion, go up as you slow the frame rate: 24p is worse than 30p, 30p is worse than 60p.. 60i is about the same, but not identical, to 30p.

The issue is how interframe compression works. If you go back to DV, you have intraframe-encoding only… each individual frame is a separate, stand-alone compression. DV is actually just a refinement of Motion JPEG… Motion JPEG was just a (sometimes) standardized way of using individual JPEG photos as a video.

In MPEG-2 and AVC, you have something just like that: the I-Frame (for “independent”). In both cases, this is similar to a JPEG frame: the image is broken up into blocks, those blocks are run though a discrete cosine transform (a kind of digital fourier transform), resulting in an reversible array of frequency info, not pixel info. The lossy part happens when this is filtered… depending on the degree of compression, the higher frequency information is tossed out of that block. The there’s a lossless compression (Huffmann encoding) of what’s left over.

Ok, that gives you your first frame. The next frame, however, it based off the first. Usually, each frame will only be a little different than the previous. Each algorithm uses various means to determine motion has occurred (one reason all encoders do not produce equally good results — the job here is well defined, but the means to achieve it is left open), then encode “vectors” to store how the image moved. There’s also a difference.. the difference between that actual next frame and what the motion estimation reconstructs, that has to be stored. This is usually very small.

When a subject moves fast, this present some challenges to the MPEG algorithms, so variable bitrate encoding can adjust to this by offering more storage for fast moving segments, less for slower moving segments. But when the whole frame moves (eg, you’re panning on a subject, versus a subject running across the visual field of a tripod-mounted camera), there’s a huge difference from frame to frame. The slower your frame rate, the more differences will occur between individual frame. And you’re getting a new I-Frame less often.

When there’s too much of that “difference” information, the MPEG algorthms kind of fall apart. You see heavy “blocking” in fast moving MPEG… that’s the result of that “difference” information being too large. MPEG blocks occur during that lossy stage. When you toss out the high frequency information in a block, you’re basically blurring things a little, merging multiple colors into one, etc. When you have too much compression, the edges of one block no longer line up with the next, color-wise, and your eye sees the edge of the block.

The best approach here is to shoot 24p for “cinematic” things.. fixed camera on a tripod, relatively slow motion… and go to 60i or 60p if you can for sports and other fast motion.

When a DVD or Blu-ray is professionally mastered for a Hollywood release, the encoding engineer has tools not built-in on any camcorder. For one, he’s got time, and a human brain. For fast motion scenes, he can apply a global low-pass filter (eg, blur everything just a little), lowering the overall information in that section of the film, allowing MPEG to encode the scene without visible blocks, because there’s less information to toss out in the lossy part of the encoder.

And of course, he can boost or cut the bitrate, at least within the limits of the format. AVCHD camcorders all record in variable bitrate, too (HDV can’t.. the tape doesn’t support variable bitrate), but there are limits.

-Dave

[David Kotlaba]

Thank you all. I will have a plenty of opportunities to practice with the 24p setting. I have now rendered a couple of projects shot at 30p to the Bluray template in vegas (1920/1080 60i) and it looks good. The resulting file size is just tiny compared to the uncompressed .avi I tried before ~ 6 GB for 30 min vs. 600 GB). Surprised this much compression doesn’t seem to reduce the quality at least to my naked eye. The Bluray template has 25 bps average bitrate as default. I am curious – does one theoretically gain anything in quality by customizing it to a higher bitrate?

Thanks again

[John Rofrano]

[david kotlaba] “The resulting file size is just tiny compared to the uncompressed .avi I tried before ~ 6 GB for 30 min vs. 600 GB). Surprised this much compression doesn’t seem to reduce the quality at least to my naked eye.”

This is because of the type of compression used. AVI files usually use intraframe compression where each frame is compressed individually. MPEG2 uses interframe compression where only the delta changes in a group of pictures are stored which are much smaller than saving every frame in it’s entirely.

[david kotlaba] “The Bluray template has 25 bps average bitrate as default. I am curious – does one theoretically gain anything in quality by customizing it to a higher bitrate?”

I wouldn’t go higher than your source. Most HDV cameras shoot 25Mbps so that is the ideal bit-rate. Adding more bits above the source bit-rate won’t add any more quality.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[David Kotlaba]

Eric and John,
Thanks again for all your valuable information.
The JVC HM GY100u shoots at a higher bitrate compared to HDV. I believe it’s 35 mbps (XDCAM-Ex in MP4 envelope) which, based on your information, should allow for less “blockiness or blurrines” when transcoding in MPEG2. (I am not using a tripod and I am panning accross a field, albeit slowly, quite often). Again, for Bluray production, I should probably keep the 30p or 60i shooting mode rather than 24p and maybe boost the variable bitrate during rendering and DVDA authoring to match the camera (i.e. up to 35?)
david

[David Kotlaba]

Sorry, I meant Dave and John.