[plug] SCSI cards

[Bernd Felsche]

On Monday 02 August 2004 08:56, Michael Holland wrote:
> On Sat, 31 Jul 2004, Bernd Felsche wrote:
> > compared to the fastest SCSI. Some of the SCSI drives have sustained
> > throughputs in excess of 80 megabytes per second; so four on each

> Given that an actual SD broadcast is less than _one_ MB/sec, thats an
> awful lot of headroom.

[I'll try not to re-iterate too many of Craig's comments]

Compressed. MPEG2, isn't it?

What the station broadcasts isn't "broadcast quality".  Broadcast
quality is what they use as their input to the process.

You want to do editing in MotionJPEG at least. Transcoding in both
directions on the fly is a RPITA and is not only compute intensive,
but the repeated lossy compression will degrade the picture quality
after just one edit.

> > 8 broadcast-quality video channels per SCSI drive.
>
> So editors use around 10x broadcast bandwidth per channel? Is this
> the normal ratio of mjpeg to mpeg2?

About 4:1 IIRC. I bought a dedicated NLE machine (Casablance Avio)
to do my editing. Haven't regretted it. Its 233MHz MMX Pentium takes
a while to compute transitions but the internal IDE drive sometimes
becomes overwhelmed when recording (digitised transcoding) from
video sources. That's a fast IDE drive as well. One that _should_ be
able to cope with 20 megabytes/second quite easily.

>  It would seem a bit excessive these days. Why not keep mpeg2 on disk,
> and decode it real-time into memory buffers for editing?

Because you get crappy quality.

> > A single PATA running at 7200 rpm is _enough_ for
> > broadcast-quality editing; but you have to be patient. If you
> > stripe and mirror across 4 drives, then there's ample bandwidth.

> I'd like to see an editor that will do 'mark-ups', and show it as
> best as it can (draft) in real-time. Then when you are finished,
> it can take as long as needed to render a high-quality version
> unattended.
> Does such a thing exist on Linux? Am I making any sense? Sorry, I
> don't know the terminology.

Story boarding, scene transitions, multi-channel sounds over
multiples scenes, multiple camera angles, ...

Rendering transitions can be very time-consuming. Video editing, if
you're finnicky and want a good result requires a time budget of
about one HOUR of work PER MINUTE of final output. That's without
any animations, really fancy titling, background music, overdubs,
commentary, etc.

Linux has been, by and large unsuitable as an operating system to
perform all of those things; especially when it comes to real-time
capture.  The 2.6 kernel promises a lot of underlying capabilities
that are essential for usability.

You can't build the final application software until the foundation
is stable.

-- 
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