Friday, January 9, 2009

SSC #85 A reader question

Dear Mr. Smith:
I recently tried to upload a video to a website, and could not get it to go. I increased my web hosting space to 20GB and still could not get it to work. I'm sure how big the video is, but it is over an hour church service. Any information/advise would be appreciated.
Now I am looking at DVD burners and duplicators. What would you recommend that would duplicate videos of that size?
Thank you,

Hello reader,

It sounds like you have an interesting problem on your hands.  I think that with a little more understanding on your part, you'll realize what is going wrong.

The first thing to understand is that video can come in a lot of different sizes for the same length.  One hour of video can be as small as 300 megabytes, or as big as 10 or 20 gigabytes.   The size of the file is a result of the codecs used, the level of compression employed within the codec, and the bitrate of the video.  Also the resolution of the video has a large part to play.

To define these terms, a codec is basically a system to encode or decode something.  There are codecs for both audio and video.  There are many different codecs for each.  You're probably familiar with MP3 files, right?  MP3's are just audio files encoded with the MP3 codec.  When you play an MP3 on a computer or a portable device, the device uses the same codec to decode the file into an audio stream.  A DVD player hooked up to your TV for instance uses the MPEG-2 video codec to decode the files on the disc and show you video.   Not all codecs are created equal.  Some are better for some tasks than others.

Bitrate is a measurement of how many bits of information per second the file uses.    The higher the bitrate, the more data is used to render each second of video and/or audio.  The more data used, the higher the quality, and at the same time, the bigger the file size.  There's also something called variable-bitrate which allows the bitrate to change over time to adjust to the needs of the video.  This makes it so that high-action scenes in the video get a higher bitrate and hence look less choppy, while scenes with little movement can use a lower bitrate to save space.

Compression is simply a way to crunch files down so that they are smaller.  If I went through this letter and every time I used the word "the" I put a number 6 in its place then by the time I got to the end of the letter, I'd have saved a lot of keystrokes.  I would just have to make sure to start out the letter by explaining that everywhere you see a 6, to mentally replace that with "the"... Compression works in the same way.  By identifying repeating patterns of data within a file, and then using a system to reduce it.

Again, to relate to something you're likely to be familiar with, MP3 is a compressed audio format.  If you were to uncompress a 4 megabyte MP3, you'd get about 20 to 25 megabytes of data.

Resolution is simply a measurement of how many pixels high and how many pixels wide the video is.  A pixel of course is one colored dot that makes up the picture.  Your computer monitor is likely displaying a resolution of about 800x600 or higher.  For the sake of arguement, we'll assume 800x600.  If you multipy the two numbers you get 480,000 pixels.  Thats 480,000 little dots of color that get updated every time your screen changes.  If each pixel only uses one bit of data for each change, then you're looking at 480k of data for each fullscreen change. And you want a decent framerate so that it doesn't look choppy, so around 30 frames per second.  So 480k times 30 = 14,400k or 14.4 megabytes of data, for one second!  or 843 megabytes for one minute or around 50 gigabytes for an hour.  Thats huge!

Thats also uncompressed and assuming that every pixel changes throughout the entire video.  But you can see that sizes can theoretically be very big, hopefully you'll also see that they don't have to be.  By reducing the resolution to 400x300 you'd reduce the theoretical size to just 12 gigabytes.  By using compression you'd reduce that to about 1 gigabyte or smaller.  And by using a codec that doesn't change the color of pixels unless they need to be changed, you'd reduce it even further.

Ok, now that you have all of that to think about, I'll try to answer your question a little more directly.  You should use a video converter to convert the file to a lower bitrate and use a more efficient codec.  Depending on what you did the recording with, your video is likely in MPEG-2 format (suitable for DVD players).  Converting it using something like the DivX or Xvid codecs could reduce the filesize by a factor of 10 if you choose an appropriate bitrate.

For hosting video on the web, you're going to want something that is small and easily downloaded.  If you intend for it to be played in a web browser then you're going to want it to be a codec that facilitates that.  I'm not sure what kind of website you're trying to use, but if the file is too big, people won't be able to stream it.  And since you said it is an hour of church services, there's not likely to be a lot of action, or the need for hi-definition quality.  So you can probably get away with a smaller resolution like 400x300 and a low bitrate (say around 500 or less).  This should end up with a file that is small enough to for people to download quickly and possibly even stream with little or no choppiness.

There are lots of video conversion tools out there.  You likely already have Windows Movie Maker on your computer, and this will convert it to a WMV video  (WMV stands for the Windows Media Video codec) which is very common and widely used.  Its very easy for beginners, but it only has the option of outputting to the WMV format, so you may find that it will not suit your needs if that codec is incompatible with what you're trying to do.   If you want to use something a little more robust with more options and that can re-encode the video in a wide array of codecs, then try out MediaCoder which you can get free at

MediaCoder is free and open source, and it will DEFINITELY re-encode your video into something you can use, though it may take a little more time to figure out how to use the program effectively.

As far as DVD burners, the capacity of recordable DVD's is 4.7 Gigabytes.  To go higher than that you'll be getting into BluRay which can be very expensive and is something that the congregation is not likely to be able to play anyway unless you buy them all BluRay players.  So in picking a DVD burner, go for speed and quality.  I can't really recommend a single brand as they all have their successes and failures, I would just recommend you search online for some reviews on individual models before you buy.  If you plan on using this to burn 10 or 20 copies at a time, it could wear out quickly if it's not built for heavy use.

If you use a program such as Nerovision Express to make the DVD it will re-encode the video to fit on the DVD, so filesize shouldn't be a problem so long as you don't expect to get 20 hours of video on a single disk.

If you try all of this and you still can't get it to upload to your site, you may have some networking issues or the site may just not allow that type of file.

I hope this helps!

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