External FW HDs and FCP not a good mix?

[ehmjay]

Hi everyone,

I was reading online today that with a Powerbook and a firewire HD and Final Cut Pro - this combination is a bad one.

People are saying that you should not do this and that it will only end up giving you problems.

Is this the case? I'd hate to think I just dropped 200 bucks on a 300gb HD only to have it be practically useless...

(I have edited a video on an external hd on this powerbook and it was prettymuch fine until i did about 3 renders into widescreen and I did recently experience a bad dump to tape but for th emost part its been fine.)

if someone could advise me that would be great.

I have FCP 5 btw.

[edDV]

Capture and DV Firewire dubs to/from an external drive are risky.

Proper technique is to capture to the internal drive*. Copy the DV file to the external drive. Edit from either. Encode to either. Move the finished product back to the internal drive before firewire streaming to a camcorder or other DV transfer device. Non-Realtime file copies can be made from either.

*A separate internal drive for capture is preferred but if a laptop, shut down other processes during DV stream transfer.

[ehmjay]

okay...well I've did have troubles capturing but I think I will take your advice for dubs.

[edDV]

DV over firewire is a stream not a file copy. Best to make the connection as direct as possible.

[ehmjay]

what do you mean stream not a copy? i'm confused...you mean if I actually captured to my internal HD i'd get a different format?

also - wouldn't it technically be waster to use USB 2.0 rather than firewire 400?

[edDV]

what do you mean stream not a copy? i'm confused...you mean if I actually captured to my internal HD i'd get a different format?

Your DV camcorder has no file system or networking capability. The camcorder can genereate a DV stream from:

1. The camera processing block (CCD to DV encoder)
2. The DV tape
3. The analog pass-through inputs (if so equipped)

DV over firewire is 25Mb/s (video) + audio, + metadata and transfer overhead. The total stream is 29-34Mb/s.

In XP, the stream transfer is managed by Directshow. The path to the internal hard drive is reasonably direct so transfer will be successful so long as the DV stream has continuous access to the drive. If the OS or a background app gets priortity on the drive, the stream bits metaphorically spill to the bottom of the case because the stream just keeps coming. You see this as lost pixels, fields or seconds. Since this is a stream, there is no error correction or resends. Some applications construct a small software buffer (e.g. WinDV) but that buffer will overflow. The datastream is converted by DirectShow to a AVI wrapped file at the HDD. From there, the file can be copied. MAC OS does the same with a DV file extension.

For these reasons transfer to a second internal drive is recommended. "PCI Bus Mastering" can isolate a drive controller to a single process so the DV transfer and OS operations can happen separately on different drive controllers.

Single drive notebooks need to have the OS and background tasks under control to stop HDD interrupt. External USB2 drives need CPU priority to process the 30+Mb/s continuous stream* to the USB2 drive. The OS and other tasks frequently take priority over the USB2 control process so again you potentially get dropped pixels, fields or seconds (more so than either internal drive).

So in conclusion, DV streams need to be managed if you don't want drops. If using a notebook, transfer to the local drive and then copy the DV-AVI (or *.dv) file to the extrenal drive.


* To put this into perspective, a continuous 30Mb/s stream is approxamately 10x your best internet connection speed and every pixel needs to arrive without error. Ethernet or other networked file copies will request packet resends if errors are detected thus assuring an error free copy.

also - wouldn't it technically be waster to use USB 2.0 rather than firewire 400?

Again you are confusing a DV stream transfer with a network connection. Consumer DV always transfers at 1x speed (~30Mb/s out of the total 400Mb/s). The bottleneck is the OS (and CPU) not the IEEE-1394 connection. This is even more the case with USB2. A typical hard drive can continuously transfer 240-720 Mb/s (30-90 MB/s) over the PCI bus but only 64-200 Mb/s (8-25 MB/s) over a USB2 connection. The 480 Mb/s spec is for burst rate only. A firewire drive will continuously transfer faster than a USB2 drive (~100-300 Mb/s) when doing a file copy under control of a network driver.

[ehmjay]

but it's not possible to put a second internal drive into a Powerbook right?

anyways, thanks for clearing this up. I've yet to really have any troubles capturing to an external drive - however I will keep this all in mind.

[edDV]

but it's not possible to put a second internal drive into a Powerbook right?

anyways, thanks for clearing this up. I've yet to really have any troubles capturing to an external drive - however I will keep this all in mind.

The older and slower the notebook, the more this becomes an issue. But all notebook or other single drive users should be aware of the increased risk.

[ehmjay]

thanks for all your help edDV. Much appreciated.