The data coming down that firewire cable is 1GB / 5 minutes, or near enough to it, that's 13GB / hour, so 10 hours = 130GB, and yes I like many others have lots of drives and lots and lots of TBs of storage. And that's just for DV25, which is pretty highly compressed.

Compressing it much more than it already is and you start to hit issues IF it's before you've finished editing it etc.

Good encoding for DVD means a bitrate of around 6 MB/sec, one can go lower, really depends on the quality of the video in the first place as to how much the qulaity will suffer. With really good quality video you can get down to half that.

Bob.

Thanks Farss & Grazie for your replies.

Grazie, per your question, Farss answered it - about a gig for 5 minutes / 200Mb per minute or so. Thats what my firewire camcorder spits out. That seemed huge to me, because (I think this is my problem) - I was encoding my edited clips at 30 - 40 Mb per minute, which I guess is about a half-Mb per second or more. That's just a fraction of the size they should be, even though they looked ok to me.

So I thought: "If I only need 30Mb per minute to go to the DVD, why do I need 200Mb coming outta my camera?"

I am still confused by the math and the terminology... when you say good DVD encoding should be a bitrate of about 6 MB/sec, is that 6 megabytes of filesize for each second of video play?

If a 2-hour video is 7,200 seconds, and each second is 6MB, that's (gets calculator out)... it's 43,000Mb, which I guess is 4.3Gb? I guess that's right. It still sounds huge to me... or is 43,000Mb actually 43GB?

Oh man... my brain hurts! I just looked at the first part of your answer again - the "13GB per hour out of the camcorder" part. That would mean I could only put about 20 minutes of video on a DVD (at that rate). Isn't that huge? So it seems like we take huge files outta the camcorder via firewire, then edit them while large, then render them to a smaller file size to burn to the DVD, so we can fit a couple of hours? Is that the general idea?

But wait! That rate of 1GB / 5 minutes is around 200MB per minute, which is 3 or 4MB per second, which is way LOWER than the 6 mb per second we want on the DVD.
This is a magic trick, right?
I am so confused.
I am so sorry - am I completely misunderstanding your info?


I REALLY appreciate any and all help understanding this.
Thanks!
JB

Time for some asprin!

Firstly don't confuse Bytes with bits!
The data is coming out of your camera the same as it was recorded at 25 Megabits / sec, that means 13GigaBytes per hour.

Now the video coming out of your camera is compressed, pretty much each picture is compressed the same way as jpeg pictures are compressed.

Video on a DVD is compressed using a smarter scheme. Not only is each picture compressed using jpeg compression but Groups Of Pictures are compressed by looking at the difference between the first picture and subsequent ones in the group. As you can see a sequence of still images doesn't need much data to define what's there, just encode the first picture and some way of saying 'more of the same' please. The standard used is mpeg-2 and my description is very much simplified. Hopefully you get the idea though, lots of motion means more data is needed, less motion, less data.

The video recorded onto your MiniDV tape doesn't care about motion, each frame or picture lives until itself, ignoring it's neighbours. Not efficient but pretty robust and goof proof.

When you encode your video to mpeg-2 for a DVD, good quality video can be achieved at say 6 Megabits per second average plus the audio data. With PCM audio you get roughly 1 hour of video onto a DVD. As you rightly worked out recording what comes off the camera to a DVD you do indeed get only 20 minutes and a disk that most devices will not play, still a good way to archive footage though.

If your video is very well shot with a good camera you can take the bitrate much lower, even down to 3 Megabits per second and still get good video from the DVD, I've even seen passable video at under 3Mbits/sec.

You can also get more room for the video by using Dolby audio, that adds about another 50% to the amount of video you can fit onto a DVD.

Please note though. Both mpeg-2 and Dolby audio are lossy encoding systems, you loose a very little to quite a lot of the quality. Not a real issue when you make a DVD, but becomes a potentially bigger issue if you want to edit what's on the DVD because it's going to go through the same lossy process again.

Hope you don't have a migraine yet.

Bob.