An email response: interlacing, aspect ratio, bitrate, etc.

I was recently helping someone with some general video editing questions using Premiere Elements (I use Premiere Pro, and I really don't know Elements that well). I ended up with a pretty lengthy response, so I thought it would be something I could post on this blog, since I hardly ever put anything here.

Original email:

Josh,

My name is ..., I spoke to ... and she said you wouldnt mind giving me some pointers using Adobe Premiere Elements. I was so impressed with the Highlight DVD that you made that I purchased the same camera that ... has and also bought Adobe Premeire Elements.

I tried to burn one of the games just to make sure it was working in "wide screen" but found that the video was very pixelated and rough. I also noticed that even though I formated it for wide screen, it was in 4.3.

I tried to use the Adobe help pages and couldnt find much help. I found a website that said I should make sure the 'average data rate" was the same on the video clip and the DVD project file. The clip is 1.1 MB / second. But I cant find anywhere to adjust that setting the project file.

Your DVD came out so smooth. Should I have bought a different version other than "Elements" or do you think Elements can suffice and theres just some tweeking I need to do.

I am a ... by trade and know how to use a computer but when it comes to graphical design and video rendering, Im kind of and idiot. Any suggestion or information that you could lend would be greatly appreciated. Feel free to reply to this email or call me at ...

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My response:

This is really lengthy, sorry. I keep a blog (which I rarely edit) and thought my response might make good content for it, so that's why this is kind of long.

Premiere Elements is a great program, and what I recommend to most people looking to edit their home videos. I actually use Premiere Pro, which is in some ways similar, but in many ways very different. In addition, I use Premiere Pro to edit, and Encore DVD to actually author the DVD. Because of that, I don't know how much help I can be, but I'll do what I can.

When I create a new project in Premiere, the first screen asks me what type of project it is: NTSC vs. Pal, SD, HD, 4:3, 16:9, etc. It has presets that cover the basics. I edited the football video in a preset called "Widescreen 48khz" which is DV NTSC, 29.97 fps, 720x480 with a 16:9 ratio and a 1.2 pixel aspect ratio (the 48Khz represents the audio sample rate).

Pixelation is generally caused by overcompression, or using too low of a bitrate when transcoding the video to MPEG2. If you are using footage directly from ...'s camera then your source is HD 1080i footage, which has to be downsampled to SD to edit and burn to a DVD (in the next little while we will be able to edit in native HD and burn to either Blu-ray or HD-DVD but for now it has to be downgraded to SD or Standard-def to put on a DVD). However, ... did not give me the native footage, but rather clips burned to DVD using the software that came with the camera. This meant that by the time I got the footage, it was already downgraded to SD and compressed to MPEG2, but it was still great quality. Premiere Pro lets me edit natively in MPEG2, but I get much better performance working with uncompressed AVI files, so I actually took all of her footage and converted it into uncompressed AVI files before working with it. I essentially copied the .VOB files from the DVD and renamed them to .MPG, then transcoded them to uncompressed AVI files. If you look at a video DVD, it will generally have several .VOB files in the VIDEO_TS folder. These are just MPEG2 files with a .VOB extension. You can just copy them to your computer, rename them to .MPG and play them. Unless of course the disc is copy protected, then you have to use decrypting software like DVDDecrypter, but that is another story.

You mentioned that the video on the DVD was smooth - that actually was a bit of work, and I actually thought it could have been a lot smoother. Although ...'s camera is HD, it is still interlaced footage (like almost all consumer camcorders), and by the time I had the footage ready to edit I thought the interlacing artifacts were very distracting. Basically, interlacing is the fact that each frame is actually composed of two fields. One field represents every odd horizontal line of resolution, and the other field the even lines. What happens is when you have quick motion (like football - especially close up shots like ... running down the sidelines right next to the camera) is that the camera captures the first field, then when it gets the second field in the frame, the picture has changed by 1/60th of a second, which doesn't seem like much, but the player has moved ever so slightly from when the first field was captured. This causes interlacing artifacts, particularly along vertical lines. It can make the footage seem very shaky, enough to make you sick in extreme cases (particularly when combined with handheld footage - even the steadiest of hands produce shaky video). By the way, I'm told you did most of the filming of the games. I thought the footage was excellent, and is definitely one of the reasons the final highlight video turned out so good. Professional cameras film in 24p (for progressive), which means that there is 24 frames per second (as opposed to the 29.97 you get in most consumer cameras) and each frame only has one field, so there is no interlacing. A lot of consumer cameras claim to film in "progressive mode" but it is generally not "true" progressive like a professional camera would do, but that's another story. For the football video, I actually deinterlaced all of the footage. This is a trade-off. You trade smoothness for clarity, sort of. Deinterlacing is accomplished in a lot of different ways by different software, but the end result is that both fields in each frame are made to be identical. If you've ever paused a movie and had some part of the picture shake back and forth, that is as a result of interlacing - one field of the frame is in one place and the other field in another place, so it alternates between them when you pause it. Anyway, deinterlacing eliminates that problem and makes the movie much more clear, especially along lines of contrast, but it can make fast motion a bit more jerky, as the advancement from frame to frame can actually become detectable to the human eye - kind of like a little flip book. It especially becomes apparent in slow motion clips. If you look at the slow motion clip of ... (I think it is ...) jumping in the air to catch the ball (I think it is in beginning of "Rock you like a Hurricane") you can visibly detect the advancement from frame to frame. Good slow motion is very hard to achieve without a very nice, true progressive scan camera. The camera you bought actually has a feature to record 12 (I think) seconds of video at a higher frame rate, so that you can do extreme slow motion and still maintain a relatively high frame rate, yielding much better slow motion or stop frames.

Ok, having said all of that (some of which you may already know), let me try and answer your questions a little more specifically. To end up with widescreen footage you want to make sure that your project settings are widescreen, and that when you export it your export settings are also set to widescreen. You can potentially edit in 16:9 and export to 4:3 and vice versa. In Premiere Pro, when you select File -> Export -> Adobe Media Encoder, you get a dialog box that lets you choose from several presets and customize them if necessary. I can verify in this dialog that it is exporting to NTSC DV 16:9. I'm not familiar with the capture process with your camera, but its capture software may also have the option to convert to 4:3 when you pull the footage off the camera.

I can also specify the bitrate in this dialog box. I usually use 7 Mbps, which gives me roughly an hour of content per disc. There is also a generic "quality" setting which refers to lossy compression and should normally be set to 5 (on scale of 1 to 5). If you are encoding to 1.1 Mbps, you are going to get a lot of footage onto one DVD, but it is definitely going to be very pixelated and choppy - the only way to fix that is to increase your bitrate. I think you may be trying to get all the games onto one disc. At full quality, you only get one hour per DVD. The reason Hollywood movies are longer is because they are using 9 GB (roughly) DVD's instead of the 4.7 GB disks available to the general public. Unless you have your movies professionally authored, you can only use 4.7 GB disks. You can get dual layer DVD's and get double the capacity, but they are not going to playback in most DVD players. You can get two hours on a basic 4.7 GB disc using a lower bitrate (like 4 Mbps), and the quality is still somewhat ok. Anything above that and you really start seeing pixelation. It could be that the 1.1 you are referring to of the original clip is actually 1.1 megaBYTES per second, as opposed to 1.1 megaBITS per second. 1.1 MBps (bytes) would be equivalent to 8.8 Mbps (bits) per second. I'm not familiar enough with the camera and capture process to know what kind of clips you are dealing with.

The reason the Adobe help file refers to "average data rate" is because files are often encoded using variable bit rate. Any given portion of the video may be encoded at a different bitrate, depending on how much action and information is in each frame. The average bitrate in megabits per second (mbps) is roughly ((file size in MBytes) / (length in seconds) * 8). You can also use a utility like GSpot Codec Information Appliance (google it for more info) to tell you everything you'd ever want to know about your video file.

I don't think your issue is with using Elements as opposed to some other video editor - it's a matter of determining what type of source clips you are dealing with, what your project and export settings are, and how much you're trying to fit on one disc. Unfortunately I can't tell you exactly how to specify project or export settings in Premiere Elements. But you will at least want to make sure that when you play (in windows media player or whatever) the original clips captured from the camera that they look OK - I'm assuming that they do, otherwise you would have noticed the bad quality when editing them in Premiere.

Anyway, sorry for the novel. Feel free to ask me any follow up or more specific questions - I promise not to be so long-winded!

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And for anyone reading this blog, feel free to post any further comments, corrections, or clarifications to anything I've said here. I'm always learning from others!