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Technical: Converting Video to DVD

Technical: Converting Video to DVD

This will show you in Layman terms the different methods companies use to transfer your video to DVD. There are many methods and types of equipment which all differ in quality. If you are shopping around then you will find this an invaluable source of information to ensure that you get the quality you deserve. Don't be fooled by price and never be tempted by cheap prices and sometimes the high price companies are either over charging or simply subbing your job out with a big mark up.

Video Encoding methods

The vast majority of video transfer studios in today’s market are “from home” studios who use their own equipment purchased from the domestic market. The major complication with domestic equipment is the digitisation (the process which converts video to DVD). These domestic machines transfer at a set fixed rate instead of a Variable rate. This set rate does not look at the length of the video or more importantly the content on the video. If you transfer a quick scene where a child is sat in a paddling pool and only looks up and waves, the encoding is done at a set low rate. Another scene where it is a moving shot of the panoramic landscape has to be encoded at a high rate. The reason for this is the difference in memory that both scenes take up. A non changing background takes up less memory than a constant change in background. If you do not vary the bit rate for each frame (remember Video has 25 frames / pictures per second) your DVD will be distorted during fast moving pictures, causing a jerking effect in parts that should have been encoded at a higher rate. The encoding is also an important factor. The DVDs mastered on domestic equipment usually have issues with some DVD players, that's why you always see amateurs quoting "our DVDs work on 95% of players" why not 100%, you now know their equipment is not professional and as a result your TV will show a jerky, pixelised movie. For the best results and peace of mind go with a professional studio!


Video Compression

Another problem is the actual encoding of the video to DVD. Professional DVDs like the movies that you buy in the store are produced in vast quantities using a unique pressing process, like a big stamper. Most of these DVDs will contain up to 9 giga-bytes of information. Custom made DVD movies like yours are not 'pressed' but encoded onto blank DVD-R or DVD+R, the “R” standing for recordable. These DVDs will only hold up to 4.7 giga-bytes that's around half the information of a mass produced DVD. This is the root of the problem.

Some studios try to match the professional DVDs and offer you 2 hours on one DVD. Simply put they are squeezing the same amount of info (video) on to a recordable DVD which can only hold HALF the information. The only way that this is possible is by compressing the material which is like putting your old Video Recorder on Long Play to get 4 hours of TV on to a 2 hour video cassette. Increasing the compression rate reduces video quality. Picture quality is referred to in BPS, bits per second, the higher the number the better the quality. One hour of footage encoded to DVD is, on average, 10 Mbps. To encode two hours onto the same size DVD the quality goes down by half to 5 Mbps. The compression rate is very important. Your footage is made up of 25 digital pictures per second at a size of 720 x 576 pixels. The amount of detail in each one of these digital pictures is determined predominantly by the compression rate and how the video is encoded.

Note: We do not just perform video transfer work for the home market. We also do work for some of the largest TV companies, Video Producers and an abundance of University research archives.



Different types of Video Encoders


One of the most important factors of converting videos is video encoding. Cheap or domestic video encoders miss a crucial process. They transfer your video direct to the DVD format of MPEG-2 and skip the AVI or DV process. This transfer of video directly to MPEG will mean that your footage will be much darker than your original footage. Once your video has been encoded, nothing can be done. Any darker bits of your video will become near black and it is irreversible. The only way to be 100% sure that you have avoided this is to have a professional studio encode your videos. Professional studios import your footage to AVI clips on a computer or to digital video (DV) before the encoding process starts. During the importing of your video the best studios will watch your movie and then adjust the levels so that the optimum quality is achieved. This is akin to processing photographs in a laboratory. The process is not as quick and the video encoders are not as cheap.

The cheapest of these video encoders can be purchased for around £1,000 from most electronics stores on the web and fit in your computer. These are called RTCC or Real Time Conversion Cards. The video input however, where the original video is fed in, on these cheaper cards are only good for analogue formats, such as S-VHS or Hi-8, and not for digital video formats such as Mini DV, DVCAM, DigiBeta. Owners of digital formats now suffer a reduction in quality by as much as 50%, this is even before the encoding has begun. Inputs for digital video are crucial if you want to take advantage of the quality of the most up to date formats.


There are two ways to encode footage VBR or CBR


VARIABLE bit rate or CONSTANT bit rate, what you want is a studio that utilises VBR. How can you tell? Pretend you have some video AVI clips on a disc and can they can convert these to a DVD. If they can not do this then they are definately using a cheap domestic setup. Remember you can purchase such equipment for around £1000 and using your computer you have yourself the same equipment that they use. If you get yourself twenty orders of £50 (20 x £50 = £1,000) and the equipment is paid for, so you can see why many companies

are popping up all over the web. On saying that, there is no comparison between the quality of this transfer and a professional transfer. If you want a high quality DVD of your video without the sacrifice of quality or resolution (dark faces) you will have to use a professional studio.



Variable Bit Rate encoding

You know that video is just a series of pictures moving fast, in fact your TV reproduces 25 frames / pictures per second. Each picture has to be encoded into a digital file. Utilising VBR (Variable Bit Rate) encoding varies the rate depending on how much of the footage changes from frame to frame. It can be compared to a cartoon. If Pluto just has to wag his tail then the next frame just the tail needs to be drawn. The rest of his body and the background can be copied from the previous frame. Because the frame has only changed by about 6% less data is needed for this video frame. Less data means it uses a lower bit rate. We therefore VARY the bit rate. This is opposed to cheaper encoders which have a fixed bit rate so each frame is given an equal data rate. This results in poor quality as it's best to vary it according to each frame.

Why vary the bit rate?

The easiest way to explain this is to detail the facts and then compare it to a real life situation. A blank recordable DVD will only hold 4.7GB of data.


If you imagine this space to be a sum of money, your weekly wages for example. It is more important to have more money to spend on the weekends, when you have time to go out for a drink or Sunday lunch, than to have the same amount of money on every day of the week. Your budget is now variable. By giving a higher bit rate to frames that change more, e.g. Pluto takes a bone to his bed, lies down and eats it, at the sacrifice of a lower bit rate for frames that changes very little, e.g. Pluto yawns.

There are diffent types of VBR. We utilise the most up to date equipment and advances in electronics technology, so our VBR encoders use a two stage process.


Stage 1 examines the source, your video footage, and determines the optimal bit rate for each video frame remember 1 second of video is 25 frames

Stage 2 encodes your video footage using the bit rate that was determined in stage 1. This ensures that the highest quality is achieved.









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