DV compression question

Robert Mann Z. · December 16th, 2002, 10:35 PM

Jeff your probably correct, i know panasonic actualy sells after market encoder chips, canopus is one of there bigger clients...

i imagine if there are diff. they must be slim considering they are built to spec with little room to wiggle...then again there is a huge diff in how sony and canon sample audio so who knows...

Rob Lohman · December 17th, 2002, 06:00 AM

Skyonic,

What I meant was that if you transfer your footage to a PC and
would view it, it had no quality degradation. In theory
if you edit the program should just pass along frames without
re-encode (but that might be an interesting thing to test).
Premiere doesn't seem to re-encode when you just edit
(without fades or any other effect except a direct cut). But I meant
that there is no loss in transfer from the camera to your
computer. What you do after that might very well alter the
quality ofcourse!

I think we are saying the same more or less, heh.

Cheers!

Jeff Donald · December 17th, 2002, 07:32 AM

My understanding is that AVI is not a codec either. It is a file format for Microsoft Video for Windows. It has various codecs available such as Cinepak, Indeo Video and DiviX. So, if I understand you correctly, AVI is a wrapper, like Quicktime.

Jeff

Robert Mann Z. · December 17th, 2002, 09:27 AM

let me see if i can shed some light on this:

ok your cam sends the raw dv into your computer, your computer must then encode raw dv, this is done on the fly....if your on a mac it encodes it using qt wrapper and qtdv codec, if your using avid on a mac it will be a qt wrapper and a avid dv codec, if your on a pc with a standard fire wire card and no other codecs installed besides preimeres default msvd codec it will be an avi wrapper and a msdv codec...

so the process of adding a wrapper to raw dv is not a problem, the codec is, not all codecs are the same, some use softeners some don't...if the test were conducted with input from a dv source into the computer you would see the same results...this is your first gen

when you render in premiere and you have no effects or transitions it should not do anything to your first gen, however if you apply a transitions, that part will be re-encoded (second gen)...

this is why there are different codecs, this is why some are prized some are not, you can be the judge which is best

:)

Bill Ravens · December 17th, 2002, 09:57 AM

Sorry to differ with you skyonic, but, when the DV file is "captured" on a PC, there is absolutely NO codec involved. There is only an AVI wrapper put on the bitstream coming from the computer. The codec is applied within the camera..and 99% of the time, the codec is/was written by Sony. The only time the codec is used, again, is when the avi file is read into the NLE software. Within the NLE, the codec is not used until the frame is modified in some way, like a transition or effect. At that point, the codec may or may not me the M$ codec, depending on the software.

Rob Lohman · December 17th, 2002, 11:23 AM

I agree 100% with you Bill! The only thing that happens when
"capturing" (which is actually a bad term for DV/1394) is that
the raw DV stream is encapsulated into a known file format like
AVI or QuickTime. The data in itself is not altered in any way
(except if you split the audio channels, but even then the audio
samples themselves are left alone)

Robert Mann Z. · December 17th, 2002, 11:58 AM

bill so you are saying that with avid xpress i can edit raw dv, i think not...avid encodes it's own codec to dv, as does matrox, canopus, pinn...and any other nle...this is simply just how it's done, in our premiere systems we can choose to use main concept or msdv on capture...same goes for canopus (canopus or msdv) on our avid station we can only use avid codecs all other will be re-coded...

>>The data in itself is not altered in any way
(except if you split the audio channels, but even then the audio
samples themselves are left alone)<<

a myth...maybe next month we will add a test to show what each looks like after capture from a dv deck...

Bill Ravens · December 17th, 2002, 12:35 PM

Skyonic....

All NLE's, including Avid, do NOT impress their own codec on the DV stream, until you load that DV stream into the NLE. Even then, the original DV file is not altered by any codecs, IN ANY WAY, until you re-render and re-save them.
This isn'r rumor, it's fact.

Go read up on the function of a codec at adam wilt's site.

Robert Mann Z. · December 17th, 2002, 01:13 PM

thats interesting, then how is it that a system like matrox which codec is rgb not native yuv is the only way to get rt effects with there board even before you apply any effects...

changing dv from yuv to rgb is what i call altering... but wait there is more

according to your post a system like canopus would work this way...you capture using your storm system to a 'non altered dv stream' ... import the footage into premiere then it gets tranfered into canopus codec?... or does it get tranfered to canopus codec after you first render?..

sorry it doesn't work that way if you are using a canopus card (for example) and you capture you will be using the canopus codec...for those of you following this and have two different codecs try the follwing capture with one then capture with another...you will see difference, for those that have a storm can see a big difference just by the color space (canopus i s 4:2:2, msdv is 4:1:1 color space) when compared with msdv...

i read adams site where does it say that codecs or for that matter custom codecs don't change anything...

John Jay · December 17th, 2002, 01:35 PM

skyonic is right on the button

if you are on a PC and you register mainconcept over the default msdv and then grab at the fast settings the vid you get is mush..

game over

Bill Ravens · December 17th, 2002, 02:12 PM

ahhhh....there is a distinction, and I'm sorry i've overlooked it in my post. HARDWARE based capture cards will use their own codec. It's only the software based capture systems(and one's that use generic IEEE1394 controller cards) that don't rely on a codec to capture. Indeed, the hardware based systems will manipulate the data stream as well as add the avi wrapper.

December 17th, 2002, 06:00 AM	#17
Rob Lohman RED Code Chef Join Date: Oct 2001 Location: Holland Posts: 12,514	Skyonic, What I meant was that if you transfer your footage to a PC and would view it, it had no quality degradation. In theory if you edit the program should just pass along frames without re-encode (but that might be an interesting thing to test). Premiere doesn't seem to re-encode when you just edit (without fades or any other effect except a direct cut). But I meant that there is no loss in transfer from the camera to your computer. What you do after that might very well alter the quality ofcourse! I think we are saying the same more or less, heh. Cheers! __________________ Rob Lohman, visuar@iname.com DV Info Wrangler & RED Code Chef Join the DV Challenge \| Lady X Search DVinfo.net for quick answers \| Buy from the best: DVinfo.net sponsors

December 17th, 2002, 11:23 AM	#21
Rob Lohman RED Code Chef Join Date: Oct 2001 Location: Holland Posts: 12,514	I agree 100% with you Bill! The only thing that happens when "capturing" (which is actually a bad term for DV/1394) is that the raw DV stream is encapsulated into a known file format like AVI or QuickTime. The data in itself is not altered in any way (except if you split the audio channels, but even then the audio samples themselves are left alone) __________________ Rob Lohman, visuar@iname.com DV Info Wrangler & RED Code Chef Join the DV Challenge \| Lady X Search DVinfo.net for quick answers \| Buy from the best: DVinfo.net sponsors

December 16th, 2002, 10:35 PM	#16
Robert Mann Z. Skyonic New York Join Date: Nov 2001 Location: NYC Posts: 614	Jeff your probably correct, i know panasonic actualy sells after market encoder chips, canopus is one of there bigger clients... i imagine if there are diff. they must be slim considering they are built to spec with little room to wiggle...then again there is a huge diff in how sony and canon sample audio so who knows...

December 17th, 2002, 07:32 AM	#18
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	My understanding is that AVI is not a codec either. It is a file format for Microsoft Video for Windows. It has various codecs available such as Cinepak, Indeo Video and DiviX. So, if I understand you correctly, AVI is a wrapper, like Quicktime. Jeff

December 17th, 2002, 09:27 AM	#19
Robert Mann Z. Skyonic New York Join Date: Nov 2001 Location: NYC Posts: 614	let me see if i can shed some light on this: ok your cam sends the raw dv into your computer, your computer must then encode raw dv, this is done on the fly....if your on a mac it encodes it using qt wrapper and qtdv codec, if your using avid on a mac it will be a qt wrapper and a avid dv codec, if your on a pc with a standard fire wire card and no other codecs installed besides preimeres default msvd codec it will be an avi wrapper and a msdv codec... so the process of adding a wrapper to raw dv is not a problem, the codec is, not all codecs are the same, some use softeners some don't...if the test were conducted with input from a dv source into the computer you would see the same results...this is your first gen when you render in premiere and you have no effects or transitions it should not do anything to your first gen, however if you apply a transitions, that part will be re-encoded (second gen)... this is why there are different codecs, this is why some are prized some are not, you can be the judge which is best :)

December 17th, 2002, 09:57 AM	#20
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	Sorry to differ with you skyonic, but, when the DV file is "captured" on a PC, there is absolutely NO codec involved. There is only an AVI wrapper put on the bitstream coming from the computer. The codec is applied within the camera..and 99% of the time, the codec is/was written by Sony. The only time the codec is used, again, is when the avi file is read into the NLE software. Within the NLE, the codec is not used until the frame is modified in some way, like a transition or effect. At that point, the codec may or may not me the M$ codec, depending on the software.

December 17th, 2002, 11:58 AM	#22
Robert Mann Z. Skyonic New York Join Date: Nov 2001 Location: NYC Posts: 614	bill so you are saying that with avid xpress i can edit raw dv, i think not...avid encodes it's own codec to dv, as does matrox, canopus, pinn...and any other nle...this is simply just how it's done, in our premiere systems we can choose to use main concept or msdv on capture...same goes for canopus (canopus or msdv) on our avid station we can only use avid codecs all other will be re-coded... >>The data in itself is not altered in any way (except if you split the audio channels, but even then the audio samples themselves are left alone)<< a myth...maybe next month we will add a test to show what each looks like after capture from a dv deck...

December 17th, 2002, 12:35 PM	#23
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	Skyonic.... All NLE's, including Avid, do NOT impress their own codec on the DV stream, until you load that DV stream into the NLE. Even then, the original DV file is not altered by any codecs, IN ANY WAY, until you re-render and re-save them. This isn'r rumor, it's fact. Go read up on the function of a codec at adam wilt's site.

December 17th, 2002, 01:13 PM	#24
Robert Mann Z. Skyonic New York Join Date: Nov 2001 Location: NYC Posts: 614	thats interesting, then how is it that a system like matrox which codec is rgb not native yuv is the only way to get rt effects with there board even before you apply any effects... changing dv from yuv to rgb is what i call altering... but wait there is more according to your post a system like canopus would work this way...you capture using your storm system to a 'non altered dv stream' ... import the footage into premiere then it gets tranfered into canopus codec?... or does it get tranfered to canopus codec after you first render?.. sorry it doesn't work that way if you are using a canopus card (for example) and you capture you will be using the canopus codec...for those of you following this and have two different codecs try the follwing capture with one then capture with another...you will see difference, for those that have a storm can see a big difference just by the color space (canopus i s 4:2:2, msdv is 4:1:1 color space) when compared with msdv... i read adams site where does it say that codecs or for that matter custom codecs don't change anything...

December 17th, 2002, 01:35 PM	#25
John Jay Major Player Join Date: Sep 2002 Location: US & THEM Posts: 827	skyonic is right on the button if you are on a PC and you register mainconcept over the default msdv and then grab at the fast settings the vid you get is mush.. game over

December 17th, 2002, 02:12 PM	#26
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	ahhhh....there is a distinction, and I'm sorry i've overlooked it in my post. HARDWARE based capture cards will use their own codec. It's only the software based capture systems(and one's that use generic IEEE1394 controller cards) that don't rely on a codec to capture. Indeed, the hardware based systems will manipulate the data stream as well as add the avi wrapper.