DV or not DV?

[Ian Hurd]

Does anyone know if the compression that the Panasonic DVX100A uses when recording to on-board miniDV is the same as it outputs through it's firewire port?

I'm sure I read somewhere that the fiewire output sends a raw DV signal but surely this must be compressed? I want to attach a portable drive, such as the FS-4, and I've read that the FS-4 can record in various formats, including raw DV - obviously this would be better than the compression used for miniDV? Or have I missed something here??

Any help would be great thanks,

Ian

[Rob Lohman]

DV is **ALWAYS** compressed. DV employs a lossy (ie, it throws
away information) DCT (JPEG like) compression algorithm that
always compresses the information per frame (intra frame
compression) at a 5:1 ratio, no matter how much or little information
is actually in a frame. This always results in 3.6 MB/s or around
13 GB per hour.

ALL DV camera's record the exact same DV signal that is layed
down to tape as that is sent over the firewire. It is 100% the
same signal. So if you where to capture while you are recording
to tape and then capture from that tape again you will get 100%
the same signal unless something is wrong with the tape (ie,
tape dropouts or other glitches).

What people are referring to when talking about RAW DV is that
this is the stream as it came from the camera, it is NOT put into
a container (see below) format like: AVI or QuickTime.

Usually these files have the .DV extension.

What is the difference between this RAW .DV file and a .AVI or
.MOV file? The difference is that in the latter cases the RAW DV
stream is put inside another format (INTACT! [although audio
streams are usually stored outside of the RAW/native DV stream.
at least in the AVI format] so that other programs can more easily
handle it (programs that can work with AVI or QuickTime files).

This is why QuickTime and AVI are known as container formats.
They just provide a format that everybody can work with, but
the data can be encoded (usually either lossy or lossless
compressed) in a variaty of different formats. You will need to
have a CODEC (decoder/encoder) installed in your system to
handle a specific video or audio stream INSIDE such a container.

Well known formats are:

- DV (it is a codec too on a computer)
- uncompressed (basically no codec)
- (HUFF)YUV
- MPEG4 (or DiVX/XviD = the same, kinda)
- Sorenson
- MJPEG
- PhotoJPEG
- Animation (codec of QuickTime)
- etc. etc.

So no, you cannot (standard, there are some ways) get an
uncompressed (truely RAW) signal from a DV camera. A device
like the firestore records the exact same information your camera
does on tape or sends out over firewire. The difference is that it
can record this information in various CONTAINER formats or the
stream exactly as it comes in (without any container format).

Keep in mind that using such container formats like AVI or QuickTime
does not degrade your signal in ANY WAY.

I hope this explained it a bit.

[Ian Hurd]

Thanks, that explains everything. I had a basic assumption that miniDV and DV were different formats but obviously they are the same.

SO, if I am streaming straight to an FS-4 would it be better to keep it in raw .DV - as this would require less processing on behalf of the FS-4 and therefore would be less likely to drop frames?

Although, firestore do boast that the FS-4's bitstream doesn't drop frames, so I guess it would be best to stay in whatever container format I will be editing within FCP.

Cheers Rob.

[Rob Lohman]

miniDV is the name of the tape format/system. DV is the name for
the complete system and the compression algorithm which is a
bit strange ofcourse because it stands for Digital Video....

Go figure... but then again they also came up with TWAIN:

Technology Without Any Interesting Name

Nope... not kidding

[Stefan Scherperel]

Ian, check out this link, you may be interested.

http://www.real-stream.com