Capturing via Firewire -- is the video compressed twice?

[MrMungus]

I have a Sony DVMC-DA2 analog > firewire converter that lets me plug in any analog source (e.g., VCR) to input into the computer via firewire.

The question is, if the converter is transferring the video to the computer as DV, which is compressed, and the video is "captured" on the PC as DV, which is compressed, is it being compressed twice?

TIA

[duhmez]

Nope. The original data is transferred to the PC. It bothers me programs call it capturing, it merely is confusing for n00bs.

[Will Hay]

It bothers me programs call it capturing, it merely is confusing for n00bs.

'Capturing' has less words, it's quicker to type than 'transferring'.
Will

[mickle]

'Capturing' has less words, it's quicker to type than 'transferring'.
Will

..... or even, less letters......

sorry Will


Mike

[Will Hay]

Nope, you got me, that was worth the shot
Will

[MrMungus]

Nope. The original data is transferred to the PC. It bothers me programs call it capturing, it merely is confusing for n00bs.

So what is the format of the data being transferred? That's where I'm getting confused.

Edit: I know it's just data but doesn't it have to be some kind of format?

What about if you transfer video from a DV camera (which is compressed) to the computer? If you do that the resulting video uses your existing capture DV codec (e.g., Mainconcept) to encode the video which the camera doesn't have. So isn't it recompressed then?

[redwudz]

DV is a AVI compressed format. Your box converts the analog signal to DV with a hardware encoder. The codec in the computer is just playing it back, not encoding or converting or recompressing it. There is no capture codec involved, just direct data transfer to your harddrive.

[lechtin]

This is a question that's been bothering me also for some time.

redwudz, if I follow your reasoning, it means that whether I capture from my miniDV camcorder with Premiere, Vegas, Studio 8, Video Studio 7, or even Movie Maker, I would get the same quality, right?

What about if I use a Canopus ADVC-100 or the like? I never used one, but it seems to me that people using it choose a DV codec (Mainconcept, Canopus, ...) during their capture (from posts I've read here).

Note: I can't say that I've noticed any difference in all the different captures I've done with various programs.

[duhmez]

if you plug the firewire from your device, into a firewire jack on the pc, then it is a lossless transfer. The DV codec on the pc is really just being used as a DEC in this situation, for playback. The format will be DV video in an avi container.

[Sulik]

If your source is analog and you're 'capturing' it through DV, then it IS being compressed to DV format, which is about equivalent to I-frame-only MPEG-2 at 25Mbps.

[MrMungus]

DV is a AVI compressed format. Your box converts the analog signal to DV with a hardware encoder. The codec in the computer is just playing it back, not encoding or converting or recompressing it. There is no capture codec involved, just direct data transfer to your harddrive.

If that were the case, why wouldn't the video transfer as the original codec is was encoded in on the converter instead of being saved using the DV codec I have on my computer? I just installed the Mainconcept codec and that's what the resulting AVI's are...and I'm pretty sure they're not Mainconcept coming out of the converter...

[FOO]

You can transfer DV to your computer with no codecs at all.
Viewing it or opening with an editor or encoder will require
a DV DEcoder

[MrMungus]

You can transfer DV to your computer with no codecs at all.
Viewing it or opening with an editor or encoder will require
a DV DEcoder

So...all a DV "codec" does is put the raw DV into an AVI format? If so, isn't "codec" a misnomer (i.e., MainConcept and DVSoft should be called encoder/decoders instead of compressors/decompressors)? Or is this assumption wrong and there actually is another level of compression when you go from raw DV to a DV AVI?

One reason I'm asking is because I'm wondering if there is a quality difference between video captured via firewire to a DV AVI and converted to MPEG-2 and video captured AS MPEG-2 (with the latter skipping the DV > AVI step)...

[donpedro]

if I follow your reasoning, it means that whether I capture from my miniDV camcorder with Premiere, Vegas, Studio 8, Video Studio 7, or even Movie Maker, I would get the same quality, right?

exactly

[donpedro]

So...all a DV "codec" does is put the raw DV into an AVI format? If so, isn't "codec" a misnomer (i.e., MainConcept and DVSoft should be called encoder/decoders instead of compressors/decompressors)? Or is this assumption wrong and there actually is another level of compression when you go from raw DV to a DV AVI?

Codec in PC is used when you EDIT. For example you add title over video for 5 seconds. Those 5 seconds (nothing else) will get re-encoded with PC CODEC.

One reason I'm asking is because I'm wondering if there is a quality difference between video captured via firewire to a DV AVI and converted to MPEG-2 and video captured AS MPEG-2 (with the latter skipping the DV > AVI step)...

Yes there is. Difference is in MPEG-2 conversion (settings, software, codec) For example by capturing DV AVI and then converting to MPEG-2 you can choose more than 1-PASS and you do not risk troubles due lack of performance.

[FOO]

Encoder = compressor
Decoder = decompressor
The "raw" DV simply gets a header attached to it becomes
an AVI. No change to the data

You last question doesn't make sense

Video CANNOT be captured to MPEG2. It may look like it , but the
capture program is grabbing bitmaps and feeding that to an MPEG
encoder which runs faster than the video.
It's exactly the same as capturing a sequence of frames as bitmaps,
storing that as an AVI, and encoding later, except that the latter
method allows a better (slower) encoder to be used.

DV is similar. The camera is doing a transformation on the sequence of
pictures before sending (or before storing on tape)

[ZippyP.]

What about if I use a Canopus ADVC-100 or the like? I never used one, but it seems to me that people using it choose a DV codec (Mainconcept, Canopus, ...) during their capture (from posts I've read here).

The ADVC-100 is a hardware converter and has a DV codec built in, the canopus one I believe (dunno for sure). If people are choosing a codec it is so that they can open the file on their PC.

[MrMungus]

Yes there is. Difference is in MPEG-2 conversion (settings, software, codec) For example by capturing DV AVI and then converting to MPEG-2 you can choose more than 1-PASS and you do not risk troubles due lack of performance.

Good point. I wasn't thinking about it that way. Thanks.

[MrMungus]

Encoder = compressor
Decoder = decompressor
The "raw" DV simply gets a header attached to it becomes
an AVI. No change to the data

Right, so, no compression is performed, just encoding is performed. I think that saying that an encoding process is the same thing as a compression process is incorrect and confusing. Encoding can involve compression but doesn't have to (such as in the case of encoding raw DV from a camera or other source to an AVI).

You last question doesn't make sense

Video CANNOT be captured to MPEG2. It may look like it , but the
capture program is grabbing bitmaps and feeding that to an MPEG
encoder which runs faster than the video.

It's exactly the same as capturing a sequence of frames as bitmaps,
storing that as an AVI, and encoding later, except that the latter
method allows a better (slower) encoder to be used.

I understand. You're saying the process is the same. The reason I was making the distinction between on-the-fly encoding and non-realtime encoding was because sometimes time is more important than quality (where the results are acceptable, that is).

Thanks.

[duhmez]

Actually, encoding is always compression, or removal of compression. A DV "capture" is merely a digital data transfer, into an avi container. an avi file is 3 things: An audio stream, a video stream, and the container that holds it all together. Almost like a kind of mini file system unto itself.

If your source is analog, then your DV encoder (canopus or whatever) is doing the encoding/compression.

[MrMungus]

Actually, encoding is always compression, or removal of compression. A DV "capture" is merely a digital data transfer, into an avi container. an avi file is 3 things: An audio stream, a video stream, and the container that holds it all together. Almost like a kind of mini file system unto itself.

If your source is analog, then your DV encoder (canopus or whatever) is doing the encoding/compression.

Right. Not to argue it too much, but, I work with computers and prefer to be precise. When it goes from the converter to a DV AVI, it's NOT being compressed again so really it's just being encoded (from raw DV, AKA DV25, to DV AVI).

I think that's right. Somebody correct me if I'm wrong.

[FOO]

DV IS compressed. I think it's around 5 to 1
DV is NOT encoded at the computer. The DV spec
and the firewire spec are related. The raw data
packets going through the Firewire are simply
put on the disk

[donpedro]

When it goes from the converter to a DV AVI, it's NOT being compressed again so really it's just being encoded (from raw DV, AKA DV25, to DV AVI).

I don't want to play with word "encoded".

When it goes from the converter to a DV AVI it's being "copied". Exact data copy. Forget about AVI wrapper.

It does not matter in what kind of paper is candy wrapped in. Candy is same.

[MrMungus]

DV IS compressed. I think it's around 5 to 1
DV is NOT encoded at the computer. The DV spec
and the firewire spec are related. The raw data
packets going through the Firewire are simply
put on the disk

Then why do I need an encoder/decoder like DVSoft or Mainconcept to view it on a PC?

[FOO]

You need a DEcoder because DV is not in a form suitable for
display.
Why do you need a browser ? Why don't you just look at raw HTML ?
Why do you need a computer , Why don't you just look at raw bits
on a disk

[donpedro]

Or... candy is just some small thing with no purpose... until you use your decoder ("taste bud" or whatever is the name of those small things on your tongue).

[MrMungus]

You need a DEcoder because DV is not in a form suitable for
display.
Why do you need a browser ? Why don't you just look at raw HTML ?
Why do you need a computer , Why don't you just look at raw bits
on a disk

I was replying to your statement that:

"The DV spec and the firewire spec are related. The raw data packets going through the Firewire are simply put on the disk"

So what I'm gathering is that yes, you can transfer raw data to your PC but no, you probably can't display it unless it's encoded.

So, in summary, the Mainconcept and DVSoft products are encoders, NOT compressors (since the video is already compressed and just needs to be encoded).

[donpedro]

So, in summary, the Mainconcept and DVSoft products are encoders, NOT compressors (since the video is already compressed and just needs to be encoded).

One last post before I'll give up on you...

All depends what you are talking about....

In MiniDV camcoder raw data from optical sensors are encoded into DV format (encoder is build in camcorder, can be Maincocept or any other). Than video data (bits and bytes) are transfered (copy) to PC. There you need decoder to be able to SEE it. Maincocept or any other.

During encoding data from optical sensors they are encoded in specific format and compressed so they don't take so much space as raw data from sensors will.

New when you start editing or creating new artificial video, one of the options is to save result into DV AVI format. In this case you will need encoder to be able to encode from pixel format to DV AVI format. Also when you modify original video in any way... you need to re-encode it again.

So that is why you need encoder and decoder.

And since data in DV AVI takes lass space than is needed to store resolution that is captured or displayed on screen, it is compressed too.

[FOO]

I give up.

So what I'm gathering is that yes, you can transfer raw data to your PC but no, you probably can't display it unless it's encoded.

Wrong ! It is already encoded and compressed and you can't view it
like that. You need to DEcode it to raw bitmaps for display.

You also need to DEcode DV to raw bitmaps before you can ENcode
the raw bitmaps to another format like MPEG2

[techgeek]

I am new to all this but this topic is something I have been wondering about also.

In my situation I just got a canopus ADVC-100. When I hook my analog 8mm camcorder to the ADVC-100 inputs and hook the firewire ouput to my computer is this what is happening:
1) hardware chip in the ADVC-100 converts the analog video/sound into DV. This DV is just DV format like DV that might come from a digital camcorder; bottom line it is DV.
2) the DV format data transfers over the firewire cable to the PC firewire port; still DV.
3) Something in my capture software takes the DV and creates an avi file where the avi file is really just a container wrapping the DV.

Is it something like this?

I have a further question. Are there different types of DV formats?

I was reading an article at tomshardware:
http://www6.tomshardware.com/video/20030530/analog2digitalvideo-04.html
and it seems to say at the bottom of the page there is DV type 1 and type2 (type1 has 1 stream for video and audio and type2 has separate streams for video and audio). Is the DV that got output from the ADVC-100 of a certain type?

Another question is that I was trying to experiment with using Microsoft Moviemaker to capture the output from the ADVC-100. When I capture I could chose what format I wanted the capture to be saved in. I could choose various wmv formats or the best quality format which I think is intended for not having any compression done. In this case where the capture software is specifying a output file mode it seems it isn't just transferring the data from the ADVC-100 to the PC but it could be compressing it to a smaller file size which would loose some of the detail. Am I understanding this right?

I just want to know what is the best way (least loss of any original data) without regard to file size to capture the data from the ADVC-100. Once I get it off of the analog tape thru the ADVC-100 to the PC in the best quality then I can figure out all the other things I need to learn about editing, converting, etc. but I at least want to make sure if I do the capture I am positioned to carry forward with the other learning.