Technology and Trends
 Video for Linux Mailing List Archives
  
List:       linux-video
Subject:    full-rate recording
From:       Adam Fritzler <mid () auk ! cx>
Date:       1999-10-10 21:25:31


What is the minimum configuration required to record full-frame-rate (even
25fps would be good) video with sound at at least 320x240?  

I'm trying to do this using a bttv on a k6-2 350mhz, 192mb RAM, recording
video to raw partitions on UDMA33 drives, using Justin Schoeman's Vstream
0.4.5.  

I've been able to capture without dropping frames for about 15seconds, but
after that it starts going down.  Frame drop rates of 20% are normal past
20secs.  If I do a 'hdparm -c 3' to the drives (setting them to 32bit I/O
w/ sync), I can get the 20% down to 6% dropped frames.  However, at around
1000 frames, it starts getting unreasonable again.  I would think my
system is adequate for doing this level of recording, but possibly not.

Are there any other apps are out there for capturing movies?

af

---
  Adam Fritzler
  { mid@auk.cx, afritz@iname.com}
    http://www.auk.cx/~mid/
  "Something in my systray is blinking wildly." -- DS 



-- 
         To unsubscribe: mail video4linux-list-request@redhat.com with 
                       "unsubscribe" as the Subject.

List:       linux-video
Subject:    Re: full-rate recording
From:       Kyle Davenport <kdd () optelnow ! net>
Date:       1999-10-11 3:29:42

Adam Fritzler wrote:

> What is the minimum configuration required to record full-frame-rate (even
> 25fps would be good) video with sound at at least 320x240?
>

(snip)

> I've been able to capture without dropping frames for about 15seconds, but
> after that it starts going down.  Frame drop rates of 20% are normal past
> 20secs.  If I do a 'hdparm -c 3' to the drives (setting them to 32bit I/O
> w/ sync), I can get the 20% down to 6% dropped frames.  However, at around
> 1000 frames, it starts getting unreasonable again.  I would think my
> system is adequate for doing this level of recording, but possibly not.

OK, I'm guessing 320x240x16bitsx30 or ~37.6 Mbps or 4.6 MBps plus more for
sound, but I don't know what compression setting you're using.  And, isn't 30
fps only every other interlaced frame?  I believe most ide drives are
incapable of sustained video storage, and you're just filling up some memory
buffer when frame rates drop.  The incredibly fast quantum atlas IV u160/m
scsi drive I have has a sustained thru-put of "13.5 to 21.5 MBps".   That
would only happen with serious optimization like renicing, TCQ'ing and
writing to the raw device (did you try that?)

Looking at vstream, he recommends raw capture, followed by compression.  He
writes, " Faster - cleaned up the compressor a bit my K62-300 now gets 60fps
compresion and decompression at 384x288".  hmmm, must be serious
compression...  I know the commercial software mpeg2 encoders (like winDVD on
the Voodoo3) recommend at least a p3-500 for "vcr-like" quality.  Looks like
he's deliberately dropping frames to keep in sync with "real time", like
audio?  He also mentions using the bit depth of the display, so if you're
running 32 bit color the thru-put requirement would double.





-- 
         To unsubscribe: mail video4linux-list-request@redhat.com with 
                       "unsubscribe" as the Subject.

List:       linux-video
Subject:    Re: full-rate recording
From:       "Jauvane Cavalcante de Oliveira" <jauvane () mcrlab ! uottawa ! ca>
Date:       1999-10-11 3:54:17

> The incredibly fast quantum atlas IV u160/m scsi drive I have has a sustained
> thru-put of "13.5 to 21.5 MBps".

Well, the IBM Deskstar 34GXP (IDE unit @ 7200 rpm) has a sustained transfer rate
of 13.8-22.9MBps
(http://www.storage.ibm.com/hardsoft/diskdrdl/desk/37gp34gxpdata.htm) and media
transfer rate of up to 35MBps, reason why I am getting one of them :-). Anyways,
usually video capture includes some compression scheme. Even if raw YUV 4:2:2 or
4:2:0 is used it is worth to remember that both chrominance signals are encoded
at half-resolution (25% of Luminance), which alone reduces considerably the
required bandwidth...  Unfortunately I don't have much experience with video
capture under Linux (I am just starting to play with it) but with a Winnov
VideumAV PCI it is possible to capture 640x480 @ 30fps under an OS not as good as
Linux  :-) (using hardware assisted compression). That makes me believe it should
be possible to achieve under Linux as well...

JVc.


-- 
         To unsubscribe: mail video4linux-list-request@redhat.com with 
                       "unsubscribe" as the Subject.

List:       linux-video
Subject:    Re: full-rate recording
From:       Justin Schoeman <justin () suntiger ! ee ! up ! ac ! za>
Date:       1999-10-11 12:28:49

> 
> What is the minimum configuration required to record full-frame-rate (even
> 25fps would be good) video with sound at at least 320x240?  
> 
> I'm trying to do this using a bttv on a k6-2 350mhz, 192mb RAM, recording
> video to raw partitions on UDMA33 drives, using Justin Schoeman's Vstream
> 0.4.5.  
> 
> I've been able to capture without dropping frames for about 15seconds, but
> after that it starts going down.  Frame drop rates of 20% are normal past
> 20secs.  If I do a 'hdparm -c 3' to the drives (setting them to 32bit I/O
> w/ sync), I can get the 20% down to 6% dropped frames.  However, at around
> 1000 frames, it starts getting unreasonable again.  I would think my
> system is adequate for doing this level of recording, but possibly not.
> 
> Are there any other apps are out there for capturing movies?
> 
> af

bttvgrab (can't remember the URL) and streamer (with xawtv) work quite well.  
The problem with Vstream is that it does not flush to disk, so when all your 
memory is used up for disk buffers, the whole lot tries to flush at once and 
frames get dropped.  In older kernels, the kernel buffer flush time could be 
set, but the newer kernels are supposed to handle this more intelligently.  
The ideal solution is (like streamer) to maintain a userspace buffer, and 
write this synchronously to disk.

-justin


-- 
         To unsubscribe: mail video4linux-list-request@redhat.com with 
                       "unsubscribe" as the Subject.

List:       linux-video
Subject:    Re: full-rate recording
From:       Bill Dirks <dirks () rendition ! com>
Date:       1999-10-13 23:23:48

Jauvane Cavalcante de Oliveira wrote:
> Unfortunately I don't have much experience with video
> capture under Linux (I am just starting to play with it) but with a
> Winnov VideumAV PCI it is possible to capture 640x480 @ 30fps under
> an OS not as good as Linux  :-) (using hardware assisted 
> compression). That makes me believe it should
> be possible to achieve under Linux as well...

I didn't make the hardware compression available with the Videum driver
yet, mainly because Linux doesn't have a codec infrastructure like Video
for W*nd*ws. If you want it, I can add it and give a description of the
decompression algorithm and sample code. The algorthm is quite simple
and not a secret. You'd have to write or modify a program to play it
back, though.

Bill.


-- 
         To unsubscribe: mail video4linux-list-request@redhat.com with 
                       "unsubscribe" as the Subject.

List:       linux-video
Subject:    Re: full-rate recording
From:       Simon Vogl <simon () tk ! uni-linz ! ac ! at>
Date:       1999-10-14 6:16:32

> Jauvane Cavalcante de Oliveira wrote:
> > Unfortunately I don't have much experience with video
> > capture under Linux (I am just starting to play with it) but with a
> > Winnov VideumAV PCI it is possible to capture 640x480 @ 30fps under
> > an OS not as good as Linux  :-) (using hardware assisted 
> > compression). That makes me believe it should
> > be possible to achieve under Linux as well...
> 
> I didn't make the hardware compression available with the Videum driver
> yet, mainly because Linux doesn't have a codec infrastructure like Video
> for W*nd*ws. If you want it, I can add it and give a description of the
> decompression algorithm and sample code. The algorthm is quite simple
> and not a secret. You'd have to write or modify a program to play it
> back, though.
> 
> Bill.
> 
Hi Bill,
don't know about others, but I'd be interested in the compression scheme 
involved - mainly because I do video analysis on compressed video data.

Is there a white paper describing the algorithm out there or a piece
of sample code??

Cheers,
Simon


-- 
---------------------------------------------------------------------------
 simon@tk.uni-linz.ac.at - icq: 14088682 - www.tk.uni-linz.ac.at/~simon

I2C-Bus 4 Linux: www.tk.uni-linz.ac.at/~simon/private/i2c
	       news://goesser.tk.uni-linz.ac.at/linux.i2c


-- 
         To unsubscribe: mail video4linux-list-request@redhat.com with 
                       "unsubscribe" as the Subject.