HDV uses MPEG2 compression. This is far from an exciting and new technology. HDV also uses tape based media - in fact it uses the same DV tapes used in you existing DV camcorder. You'd be forgiven for thinking this radical new standard is nothing new and certainly not radical. But you'd be wrong. The radical departure in HDV isn't the storage method, but the resolution of the image - put simply, it's much better. Standard Definition's resolution of 720 x 576 seems paltry to the maximum image resolution of x x 1080 in HDV. So the advantage here is a highly defined image, displayed perfectly on large screens.

With this increased resolution comes an increased data rate - the amount of data required to digitise and display video per second. If the same compression technology used in DV was applied to HDV, you'd get just 12 minutes of video on a 1 hour DV tape. Even if you felt this paltry 12 minutes was enough, the tape would have to spin at 5 times the speed to keep up with the data rate! To make things more manageable, HDV uses MPEG2 compression - and the logical solution was to use a compression rate to bring the data rate to the same level of DV - 25Mbits per second (note: this is Megabits, not Megabytes!)

MPEG2 is a somewhat ineloquent solution. Although substantially reducing data rates, the MPEG2 compression technique is an important factor in editing. Whereas DV achieves compression by analysing and compressing data *within* one frame only, MPEG2 compression uses intra-frame comparison, where one frame is compared to the next. Put simply anything looking the same in two consecutive frames is repeated. More specifically, MPEG2 uses a Group of Pictures (GOP) structure, which takes a series of frames and puts them together in a group. These groups are made of different types of frames, generally "I" frames which are compressed frames that do not depend on other frames, and P and B frames which are based on predicted results from adjacent frames. But here's the important bit: these P and B frames can't be uncompressed independently because they rely on the I frame in their particular group. DV edits so beautifully as all frames are I frames.

The impact of this type of compression is on editing and potential dropped frames - MPEG2 was designed for content delivery, not editing. With a long GOP structure, isolating individual frames is a difficult task. And if you drop one frame in capture, you lose all the associated frames in the group - so rather than the one dropped frame in DV, you get 12 in HDV. And it doesn't stop there. Because of all this compression going on, HDV is more lossy than DV and its unwise to recompress HDV, so you can forget about exporting to HDV and importing to another application.

That's the problem, how do you deal with it? Yet more expense. In order to achieve frame accurate edits of MPEG2 streams, they need to be uncompressed. (If you try and edit them in their "native" form, scrubbing the timeline is frustrating and inefficient due to the complexity of the streams as mentioned above). Editing in HDV becomes effective by either using a proprietary high definition codec for editing or by using a plug in for your editor. Both of these let you edit in real time (although the transcoding to another codec will involve a one off delay before editing!).

The good news is that just about every version of your favourite non-linear editor is offering support for HDV - but every plugin I've seen so far comes at a relatively high price. The Mainconcept HD plugin for Adobe Premiere is over half the price of Adobe Premiere itself.