Forums > Jitter

simultaneous record and playback @ 640×480

March 18, 2008 | 8:17 pm

I’m trying to capture short video clips(@640×480), which then can be played back randomly WHILE still being able to capture more clips.

Seems simple enough, but I assume there are problem inherent in this; namely asking a hardrive to both capture and play at the same time at this quality. As tested, it does seem to work in the end, however while a clip is playing and I start capturing, the clip playing glitches for a second or so. Still it seems to record OK though (DV, set at lossless).

I’ve looked at these pages with no clear answer.

Possible answers i came up with after looking at the forum:
1) being able to use an applescript or what ever to duplicate recorded clips to a second hardrive (from which clips are played back from), while it’s not recording. Though I don’t know squat about scripting, in tests playing back the clips looked fine while copying files to that hardrive.

2) toggle so that while Jitter is recording to HD#1, it is playing back clips from HD#2. On the recording of the next clip it is switched; recording to HD#2, playback from HD#1. In theory this should work, the only problem is that you can never play back all of the clips recorded. (but maybe that’s not really a problem).

3) Could it be my machine? I’m now running this off of G4 PPC power book @1Ghz. Maybe I need something beefier.

any suggestions


March 19, 2008 | 9:45 am

On 18-mrt-2008, at 21:17, ted wrote:

>
> I’m trying to capture short video clips(@640×480), which then can
> be played back randomly WHILE still being able to capture more clips.
>
> Seems simple enough, but I assume there are problem inherent in
> this; namely asking a hardrive to both capture and play at the same
> time at this quality. As tested, it does seem to work in the end,
> however while a clip is playing and I start capturing, the clip
> playing glitches for a second or so. Still it seems to record OK
> though (DV, set at lossless).

Hi ted,

I have solved the glitch problem for various projects using a RAM disk,
both on XP and OSX. for a recent post see

http://www.cycling74.com/forums/index.php?t=rview&th=30452&rid=0

the central idea is that a RAM disk
- has less delay when starting up a new movie with jit.qt.movie
- has less trouble accomodating simultaneous read & write.

the issue with a RAM disk is that it is too small to hold all clips.
so in addition you need to move clips back and forth between RAM disk
and your hard drive at well chosen points in time.
for this you need some scripting, as there is no max object to move
files
around on your disks.

> 3) Could it be my machine? I’m now running this off of G4
> PPC power book @1Ghz. Maybe I need something beefier.

this machine is capable of running the RAM disk solution, I had one
myself.
However, that was not with DV streams but with 120×160 frames.
DV is quite CPU intensive. that may be too much for your powerbook.

one solution:
buy a second hand mac mini for capturing to a local RAM disk,
after completing the capturing of a clip, copy it to its hard drive
and on your powerbook copy the files from the mac mini over the 1Gb/s
network into a RAM disk on your powerbook for playback.

HtH
-jennek


March 19, 2008 | 9:31 pm

jennek

thanks for getting back. well, I’ve made a few discoveries that you might be interested in. By using two computers, one running a record patch and the other a random playback patch both sharing a single hardrive (networked together), I was able to do both record and playback from the same hardrive, without any noticible glitching. Go figure???

conclusions:

A.It doesn’t seem to be an issue of the hardrive itself.
B. That Jitter on a single computer can’t deal with running both opperations at the same time.

or

C. That my computer can’t deal with doing both at the same time, and it’s not Jitter’s problem.

I’d be interested if you’d tried this. So, I’m thinkng of getting two mini’s, each running one opperation. Have you worked much with the mini’s. I’ve heard mixed reviews about their limited video capiblities. good points that there small relatively cheap, in case of problems. any experience?


March 19, 2008 | 10:26 pm

On 19-mrt-2008, at 22:31, ted wrote:
>
> jennek
>
> thanks for getting back. well, I’ve made a few discoveries that
> you might be interested in. By using two computers, one running a
> record patch and the other a random playback patch both sharing a
> single hardrive (networked together), I was able to do both record
> and playback from the same hardrive, without any noticible
> glitching. Go figure???
>
> conclusions:
>
> A.It doesn’t seem to be an issue of the hardrive itself.
> B. That Jitter on a single computer can’t deal with running both
> opperations at the same time.
>
> or
>
> C. That my computer can’t deal with doing both at the same time,
> and it’s not Jitter’s problem.
>
> I’d be interested if you’d tried this. So, I’m thinkng of getting
> two mini’s, each running one opperation. Have you worked much with
> the mini’s. I’ve heard mixed reviews about their limited video
> capiblities. good points that there small relatively cheap, in
> case of problems. any experience?

ted,

that is good news.
however, the comparison to jitter on your powerbook is not fair.
two computers gives you two cores with two independent jitter processes.
you might have achieved the same with a dual core machine plus having
two instances of jitter
(by building two standalones for example).

about the mini:
indeed the intel mac mini is limited in
- bandwith (as the GPU uses main RAM memory as its graphics buffer,
sharing bandwith with the CPU)
- OpenGL power (so you cannot do very sophisticated shaders)
but it might just be good enough for straightforward playback of a DV
stream,
using all of the performance optimisation tricks that you can find on
this forum (like "direct to window").
However, the G4 mac mini has separate VRAM — and much slower main
RAM than the intel minis.
So it’s hard to tell.

another way to test this: if your powerbook G4 1GHz can handle the DV
playback (with a bus speed of 133 MHz),
I am confident that the mac mini G4 1.42 GHz can also do it (with a
bus speed of 333 MHz).
compare their specs on http://www.apple-history.com

and if you are developing on a G4 powerbook, it is much easier to
have a G4 mac mini anyway.
It enables you to exchange tools and stand alones without considering
fat binaries and all that.

good luck
-jennek


March 20, 2008 | 10:56 am

actually there IS an object that does this (on OSX):
fscopy, part of the Jasch Objects library

http://www.maxobjects.com/index.php?v=objects&id_objet=4133

>On 18-mrt-2008, at 21:17, ted wrote:
>
>for this you need some scripting, as there is no max object to move files
>around on your disks.


March 21, 2008 | 6:44 am

Ah, good to know. Thanks,
-jennek

On 20-mrt-2008, at 11:56, eth1394 wrote:
> actually there IS an object that does this (on OSX):
> fscopy, part of the Jasch Objects library
>
> http://www.maxobjects.com/index.php?v=objects&id_objet=4133
>
>
>> On 18-mrt-2008, at 21:17, ted wrote:
>>
>> for this you need some scripting, as there is no max object to
>> move files
>> around on your disks.


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