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What is DivX?

DivX is a useful Codec for compressing video. There are several similar flavours of the Codec, based on the MPEG 4 specifications for compression. When used wisely it can shrink a video file by approximately a fifth whilst maintaining a good image quality. It is also the a file format commonly used for distributing large video files around the internet.

As I've already mentioned, there are several flavours of the format, the most common are DivX 3, DivX 4 and DivX 5 - each are distinctly different Codecs based around the MPEG 4 format, as well as the common Xvid variant of the Codec. Rather that delve deeply into the minefield of techniques for converting, I will give you some over-arching tips and pointers to more in depth guides and software to use if you choose to make the extra step of making a DivX version of your file.

Do you need to convert your format?

Its fair to say that for many this is an unnecessary part of the process - a finished DVD of the MPEG 2 will be sufficient. Personally I like to make the conversion for general using. AS I've already mentioned around these parts, I'm quite anal in my desire to keep these discs archived in some way or form. I also enjoy having a number of multi-title discs at my disposal for general use.

Basically, DVD can be a flaky medium if not looked after, so I keep the full quality DVD as an archive copy, and then use the DivX version for general viewing. The added benefit is that I can then get 5 or 6 titles onto 1 DVD - cutting storage space drastically. The master then goes into a nice dark cupboard to hopefully never be required again.

Software options for converting MPEG 2 to DivX (and back again if required)

DivX is nice and easy if you captured in .AVI - but as we haven't there are limited options for easy conversion. Two tools do an excellent job. The first, DrDivX is a breeze to use and should be easily straight forward to even a beginner as it keeps a lot of the complicated stuff under the hood. That said - the more demanding user can tinker and fiddle with the advanced options.

Normally, converting to DivX can be a many stage process, with some tricky estimates involving filesize and bitrate. DrDivX is very good at predicting the finest file size and bitrate automatically, on the parameters you give it. It also has some support for restorative VirtualDub filters, but can be a bit flaky with them. The downside of this product is it locks you into one codec - DivX 5. This is fine for most, but more demanding users may feel a bit hemmed in by this. It also doesn't make as clean an encode as its more powerful competitor, VirtualDub MPEG.

For the more demanding user, VirtualDub MPEG is the tool of choice. Better still it is free. Normal VirtualDub works only with .AVI files. The MPEG version is a mod of the original version built to handle MPEG video as well as .AVI. There is lots of stuff to fiddle with in the programme and a wide range of filters that can be used. There is a basic guide to setting DivX compression here.

And finally... DivX resolutions, bitrates and two pass encoding

If you are converting to DivX (or Xvid) then what sort of settings do you need to consider? There's as many methods of setting up your DivX as there are people using DivX as compression. I can give you my insights, but this only covers the (simplistic) way I've become happy doing it. The things you need to consider are applicable across the range of applications and especially DrDivX and VirtualDub / VIrtualDub MPEG.

Firstly, although captured in full DVD specification MPEG 2, its a good idea to drop the resolution to aid compression to DivX. There is an option in the DivX configuration settings to allow you to resize the finished file. There are a number of things to consider - DivX has some mathematical principles that need to be adhered to - there is an excellent guide to resolution whys and wherefore's at the excellent Doom9 site.

Personally, I go for 512x384 or 480x368, depending on which frame of mind I'm in. The smaller the resolution the less pixels to process. For me these two sizes are a good trade off between quality, detail and compressibility. When played on a large TV via a DivX Hardware player, the results will be pretty good. It'll never be better than the VHS, as its only ever as good as the source.

As for the Bitrate, its dependent on the final file size you're aiming for and the length of the movie. As far as DivX goes, if its around 90 minutes long, you'll be looking at a bitrate of approximately 950-980kbps. For the best quality, the two pass encoding method is also recommended. Basically the first pass analyzes the video file for compression, whilst the second pass optimizes and executes the compression. You'll find more info on two pass encoding at Doom 9.

Conclusion

Capturing and saving your prized tapes can be a time consuming business. However, the rewards of learning a lot of this stuff and doing it for yourself are immense. I haven't even scratched the surface of the thin skin on the surface of this topic. Hopefully as an introduction it will give you some insights into the considerations, the processes and the pitfalls. Look around the many sites linked here for in depth info, persevere and keep those tapes from rotting!

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