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List:       linux-video
Subject:    [video4linux] Video editting
From:       gsstark () mit ! edu
Date:       1998-08-19 23:06:27
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So, a friend just came back from film school for the summer. There she
used macs with two monitors and frame grabbing hardware for doing
serious video editting, the software was from Avid and Adobe. 

She said digital video editting is great, but 
 ``I just wish it didn't crash so much''

How far are we from actually being able to do such work on Linux? 
Are these frame grabbing boards up to the standards of professional
systems? I'm not sure exactly what that entails, whether it's just a
matter of quality or there are obscure features they need (timecodes?
drop-frame stuff?)

Also, I have a hardware question, can a PCI frame grabber write frames
directly into the video memory of an AGP video card? 

greg

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List:       linux-video
Subject:    Re: [video4linux] Video editting
From:       Alan Cox <alan () cymru ! net>
Date:       1998-08-19 23:10:43
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> How far are we from actually being able to do such work on Linux? 
> Are these frame grabbing boards up to the standards of professional
> systems? I'm not sure exactly what that entails, whether it's just a
> matter of quality or there are obscure features they need (timecodes?
> drop-frame stuff?)

No idea

> Also, I have a hardware question, can a PCI frame grabber write frames
> directly into the video memory of an AGP video card? 

Yes. AGP is just across a PCI bridge
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List:       linux-video
Subject:    Re: [video4linux] Video editting
From:       gsstark () mit ! edu (Gregory S !  Stark)
Date:       1998-08-30 18:18:18
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Alan Cox <alan@cymru.net> writes:

> > How far are we from actually being able to do such work on Linux? 
> > Are these frame grabbing boards up to the standards of professional
> > systems? I'm not sure exactly what that entails, whether it's just a
> > matter of quality or there are obscure features they need (timecodes?
> > drop-frame stuff?)
> 
> No idea

Ok, I asked questions about what professional video editting requires. The
main thing is that they need to be able to grab clibs about a minute long and
capture every single frame without dropping even a single frame. 

I've watched a video capture program on Windoze once and it was dropping a
frame every 20s or so. Assuming a bernoulli distribution that means they would
have to try about 64 times on average before they would get the whole 1 minute
clip without losing a frame. (It's also possible it isn't a time-independent
distibution and the dropped fames were caused by a repeating feature of the
NTSC signal).

Was that rate of dropped frames characteristic of the hardware? Or was it due
to the software or the OS? If it's typical of the hardware I suppose it would
be possible to implement a grabber program which let you grab twice and
synchronized the clips based on a frame by frame comparison.


Also, I'm told serious work couldn't be done on-line on the computer. Anything
output from the computer to VHS was too low quality and looked digitized. Is
that true of this hardware too?

(Instead they grabbed low-quality clips with timecodes, editted the clips on
the computer, then outputted an edit decision list, which they took to a place
where they did a linear tape-to-tape copy cut according to the decision list.)

> > Also, I have a hardware question, can a PCI frame grabber write frames
> > directly into the video memory of an AGP video card? 
> 
> Yes. AGP is just across a PCI bridge

I'm not sure I understand this, I think I'll go back to my nice simple world
of software. :) Actually if you could point me to some basic primer on PCI and
AGP stuff, I would appreciate it. 

greg

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List:       linux-video
Subject:    Re: [video4linux] Video editting
From:       Daniel Dunbar <ddunbar () diads ! com>
Date:       1998-08-30 19:13:18
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Gregory S. Stark wrote:
> 
> Alan Cox <alan@cymru.net> writes:
> 
> > > How far are we from actually being able to do such work on Linux?
> > > Are these frame grabbing boards up to the standards of professional
> > > systems? I'm not sure exactly what that entails, whether it's just a
> > > matter of quality or there are obscure features they need (timecodes?
> > > drop-frame stuff?)
> >
> > No idea
> 
> Ok, I asked questions about what professional video editting requires. The
> main thing is that they need to be able to grab clibs about a minute long and
> capture every single frame without dropping even a single frame.

no... professional editing needs continous (no burst speed stuff) capture... not
1 minute... not 2 minutes... 30 minutes or so, maybe an hour...

really support has to be there for interfacing with external betacam decks, etc.
for timecode and batch clip dumping.

> I've watched a video capture program on Windoze once and it was dropping a
> frame every 20s or so. Assuming a bernoulli distribution that means they would
> have to try about 64 times on average before they would get the whole 1 minute
> clip without losing a frame. (It's also possible it isn't a time-independent
> distibution and the dropped fames were caused by a repeating feature of the
> NTSC signal).

that was probably just hardware.... i can capture 720x480 30fps with cd-quality audio
w/o dropping frames under windows.... 
 
> Was that rate of dropped frames characteristic of the hardware? Or was it due
> to the software or the OS? If it's typical of the hardware I suppose it would
> be possible to implement a grabber program which let you grab twice and
> synchronized the clips based on a frame by frame comparison.

hardware... of course the fact that the software is bloated means it might take more
hardware to get the correct results... but it isn't because windows has some built in
unability to capture full-frame video w/o dropping frames.

> Also, I'm told serious work couldn't be done on-line on the computer. Anything
> output from the computer to VHS was too low quality and looked digitized. Is
> that true of this hardware too?

thats not really true... vhs is definatly too low quality, but lots of commercial
style work is done on a nle (non-linear editer) online these days, and dumped to betacam
afterwards... even film stuff is/can be edited on computer and dumped back to film.

> (Instead they grabbed low-quality clips with timecodes, editted the clips on
> the computer, then outputted an edit decision list, which they took to a place
> where they did a linear tape-to-tape copy cut according to the decision list.)

that is done a lot too... mainly for film and tv series stuff though.

at the end, the main reason you can't do professional or semi-professional or really
even amateur video editing under linux is because of the lack of software.... at the
moment the best you can do is playback captures with xanim and maybe (tediously) edit
them in gimp....

with a semi-decent software package and support among the drivers for the cards that
support it for video exporting (is there such support now? i haven't seen it on any
cards that i can recall) you could do at least low-end editing on linux...

time will tell....

> 
> > > Also, I have a hardware question, can a PCI frame grabber write frames
> > > directly into the video memory of an AGP video card?
> >
> > Yes. AGP is just across a PCI bridge
> 
> I'm not sure I understand this, I think I'll go back to my nice simple world
> of software. :) Actually if you could point me to some basic primer on PCI and
> AGP stuff, I would appreciate it.
> 
> greg
> 
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-- 
daniel dunbar             Those who dream of tachyons are
ddunbar@diads.com           condemned to eternal sleep.
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List:       linux-video
Subject:    Re: [video4linux] Video editting
From:       Alan Cox <alan () cymru ! net>
Date:       1998-08-30 20:06:09
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> Ok, I asked questions about what professional video editting requires. The
> main thing is that they need to be able to grab clibs about a minute long and
> capture every single frame without dropping even a single frame. 

Ok the bt848 chip can do that providing you have somewhere to put the data
that can keep up too.

> Was that rate of dropped frames characteristic of the hardware? Or was it due
> to the software or the OS? If it's typical of the hardware I suppose it would
> be possible to implement a grabber program which let you grab twice and
> synchronized the clips based on a frame by frame comparison.

Its probably a combination of hardware constraints, software limits and OS
timing ability. 

> Also, I'm told serious work couldn't be done on-line on the computer. Anything
> output from the computer to VHS was too low quality and looked digitized. Is
> that true of this hardware too?

Everything I learned about image editing is that you always output and work
to a higher quality than your target media. That is SVHS is the minimal
input/editing media for VHS


> the computer, then outputted an edit decision list, which they took to a place
> where they did a linear tape-to-tape copy cut according to the decision list.)

Makes sense. Keeps the images in the analog domain

> I'm not sure I understand this, I think I'll go back to my nice simple world
> of software. :) Actually if you could point me to some basic primer on PCI and
> AGP stuff, I would appreciate it. 

When doing overlay or capture the BT848 does DMA transfers. PCI cards can
DMA to any PCI "target" - other memory resource on the bus - that includes
main system memory (capture mode), video memory (overlay). PCI bridges
link multiple PCI busses together (you can only put 4 or 5 loads on a PCI
bus so you end up needing a tree of them). AGP looks to PCI like a PCI bus
but is a faster (133Mbytes/second) single device interface meant for
video cards. The BT848 doesnt know the difference.

Alan
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