DIGITAL VIDEO TECH

[flatbottom]

Some questions have came up in the past about USB Transfer VS Firewire Transfer from cams to the computer. Here are real numbers of data rates. These are the max rates considering everything else in the computer is up to speed, cpu speed, hard drive speed, memory speed, hard drive space, size of memory sticks. Copy these down. When buying a new computer, cam or upgrading the computer you have, consider the numbers below. USB is a shared speed of all the combined devices you have attached to the USB ports that are in use when capturing dv avi video.

Cams with hard drives used to record the video can use USB. The video is already compressed in a mpeg2 format. The data transfer can be slower so USB will work. I will be adding to this as needed.

Full MiniDV and Digital8 video which is called DV AVI (or D25) is recorded to tape at about 30 Megabits Per Second (Mbps) or about 13.5 GB per hour.

USB 1.1 has two speeds with a maximum transfer rate of 12 Mbps.

USB 2 "Low Speed" I believe has a maximum transfer rate of 1.5 Mbps
.
USB 2 "Full Speed" has a maximum transfer rate of 12 Mbps
.
USB 2 "Hi-Speed" has a maximum transfer rate of 480 Mbps
.
IEEE 1394a has a maximum transfer rate of about 400 Mbps.

The problem is that most MiniDV camcorders and all Digital8 camcorders with USB do not output USB 2 Hi-Speed which means of the approximately 30 Mbps needed to be transferred, only approximately 12 Mbps gets transferred. What that does to your quality varies. It may have no sound, the image size is reduced to approximately 480 X 320 (or smaller) instead of the NTSC standard 720 X 480, the video may stutter, skip or have large pixel blocks. Or you may get lucky..... Spending my time on a video...I will consider the numbers than feel lucky !

Flat

[ifish4tuna]

Yo Flat, I'm not following you. I will be in the mkt for a new camcorder comes spring so want to make sure I'm getting what you're trying to express.

I'm having trouble w/ your last paragraph regarding only transferring at 12 when 30Mb/s is needed and the effects. I'm not sure why the effect wouldn't be absolute, and not varying as you describe.

Is there a specification on the MiniDV cameras that identify if they do or don't adhere to the 30Mb/sec requirement? Or are you saying this is a non issue if using a firewire transfer...

I've been taking all my old vids off the 10 year old camera with pretty good success. I haven't yet gotten to the fishing vids yet. Still on kids being born, etc. The camera I'm retrieving vids from is not MiniDV. I'm just using the RCA jacks and feeding that into a pinnacle hardware device about the size of your hand, and then USB2.0 into my 'puter.

I have not yet started retrieving the vids from my MiniDV sony camcorder (4 years old), so don't know if I'll suffer from the problem you are describing. I will be using the MiniDV connector that goes to the Firewire card on the 'puter. So are you saying that should not be a problem. But would be a problem if I was trying to go directly using USB??????

Can ya elaborate a bit more for me.

Thanks, Ed

[tolmaz]

whew...over my head!

[flatbottom]

I'm having trouble w/ your last paragraph regarding only transferring at 12 when 30Mb/s is needed and the effects. I'm not sure why the effect wouldn't be absolute, and not varying as you describe.

Is there a specification on the MiniDV cameras that identify if they do or don't adhere to the 30Mb/sec requirement? Or are you saying this is a non issue if using a firewire transfer...

Answer 1
the effects will vary. Dropped frames, sound distortion, blocky frames or a combo of all. Kind of like a rain storm in between a dish network receiver and the down link from a satellite. You know how the TV screen half fills for moments, then clears up. This will happen when capturing (dv avi) video to the computer @ a speed lower than 30mbps

Answer 2
The older analog cams did not need firewire, The picture was smaller when captured and frames had less data to process. This is a none issue with newer mini dv, dv avi, digital high 8 cams of today. As noted. The dvd cams or hard drive cams can utilize the USB 2 port, as the video is already compressed, so the maximum of 30 mbps is not needed. 12 mbps is fine for a compressed smaller file(mpeg file)

dv avi is uncompressed data. Files size is large
mpeg 2 is a compressed data. File size is smaller

a comparison
a song on a cd is 35 megs(uncompressed)
the same song compressed in a mp3 format is 3.5 megs(approx)

you notice how fast a mp3 file downloads and plays compared to a uncompressed 35 meg file ripped from a cd. Hope this helps....Flat

[ifish4tuna]

Gotcha - thanks.