Hello Rua,
I looked into your code and come over this line:
QTTime durationqt = QTMakeTimeWithTimeInterval(timeStep);
The QTTime is a struct of two integers, which proberly don't reflect your
"timeStep" when calculating the fritction timeValue/timeScale. The function
QTMakeTimeWithTimeInterval() just picks a timeBase, unfortunately a "wrong" one.
Check it with the debugger what exactly the values for timeValue and timeBase
are. You may want to set them programmatically or even go the way back:
timeStep = durationqt.timeValue / durationqt.timeScale;
Another (more accurate) solution would be using the movie duration for the
render time:
QTTime currentMovieDuration = [mMovie duration];
[renderer renderAtTime: currentMovieDuration.timeValue /
currentMovieDuration.timeScale arguments:nil];
(You may have to take your intro duration into account for the rendring time as
well, I didn't looked at this part of your code)
best,
Achim Breidenbach
Boinx Software
On 02.10.2010, at 01:02, Rua Haszard Morris wrote:
> Aha - Indeed this is very accurate! (Nice animation by the way)
>
> I tried this on one of my tunes using playback in quartz composer, and it
> stuck nicely to the kick.
>
> However it drifted when I used my rendering app (qtzrendang.googlecode.com),
> so it's likely a timing bug in that or some other interaction.
>
> What do you use to render your compositions & attach the audio?
>
> thanks for the help
> H
>
> --
> http://cartoonbeats.com
> http://haszaristwocents.blogspot.com
> http://myspace.com/haszari
> http://last.fm/music/Haszari
>
>
> From: George Toledo <[email protected]>
> To: Rua Haszard Morris <[email protected]>
> Cc: [email protected]
> Sent: Sat, 2 October, 2010 10:40:41 AM
> Subject: Re: bpm-accurate LFO for quartz composer?
>
> Err, sorry for the string of responses, it's just that I re-read your note
> about every second beat. If you take the instance where I have a half note
> beat, and offset phase by 180, then you will have it hit on the 2 and the 4
> (eg., typical snare hit), instead of the 1 and 3. Using phase will control
> your offsets, and "groove" (eg., slightly ahead or behind beat).
>
> Also, I've capped the whole note at sequences of 4, but you could leave it
> unranged, so that it becomes a measure count. If you change a chain to
> generate 8th notes or 16th notes (or 3/4 time), you can adjust the associated
> range patches accordingly, so that they actually keep track of that count.
> Just throwing out some related thoughts that will hopefully help you in your
> quest for tight synchronization.
>
> -GT
>
> On Fri, Oct 1, 2010 at 5:32 PM, George Toledo <[email protected]> wrote:
> BTW, please let me know if you do experience any drift in using this, as
> there isn't any reason that I'm aware of that would cause it with this. I've
> run it for a couple hours alongside a drum machine and had it keep lock.
>
> -GT
>
>
> On Fri, Oct 1, 2010 at 5:26 PM, George Toledo <[email protected]> wrote:
> As a matter of fact, I made something not that long ago for just this
> scenario.
>
> I am attaching the "beat engine" that I used to synchronize this:
> http://vimeo.com/15191953
>
> I'm using "square waves" so that a hard tick is generated on the counter, but
> you can change wave types to generate the other kinds of envelopes that
> should be familiar from synthesis via the LFO.
>
>
>
>
> On Fri, Oct 1, 2010 at 4:50 PM, Rua Haszard Morris <[email protected]> wrote:
> Hi list,
>
> I've been trying to animate in time with music by using LFOs running at bpm
> related rates. The bpms tend to be 128/130ish so are not nicely related to
> frame
> rates (e.g. 120bpm would be!).
>
> I can't seem to get accurate sync between my audio (which is at a known tempo)
> and the LFOs - the LFOs seem to drift. I think this is the accumulation of
> rounding error over the course of the animation.
>
> I wrote a BPM-LFO plugin so as to avoid rounding issues, supplying tempo in
> BPM
> instead of period, and this LFO seems to drift just as much.
>
> Has anyone used LFOs for roughly bpm-accurate synched animation over the
> course
> of about 5 minutes? If anyone's succeeded I'd love to know how to do it!
>
> BTW my needs are reasonably modest - things like an image that flashes every
> second beat over the course of a whole song - e.g. 64 times a minute, or a
> billboard that slides into view every 16 bars (64 beats) - but the LFOs need
> to
> ensure these elements stay in phase with the audio beat.
>
> thanks
> Rua HM.
> --
> http://cartoonbeats.com
> http://haszaristwocents.blogspot.com
> http://myspace.com/haszari
> http://last.fm/music/Haszari
>
>
>
>
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> --
> George Toledo
> [email protected]
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> --
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