Re: QuickTime playback jitter

Subject: Re: QuickTime playback jitter

Date: Fri, 13 Jul 2007 23:43:22 -0400

Delivered-to: email@hidden

Im either being particularly stupid today or this is not a sufficient explanation for me to fully understand.

How is continuous different from "continuously incrementing the frame counter?"

When I hit play in quicktime I imagine someplace there is a timer. This timer looks at the QTUnit timebase and figures out how often it has to decompress the audio/video/timecode etc track. (right?)

Are you saying the asynchronous playback will pre-fetch or pre-decompress outside of the timer ? like some sort of thread analogy, and pre-store the decoded frames in ram to be fed to QT Player when the timer indicates that said frame is needed? And that this is more efficient because its outside of some main run loop or something?

Obviously by manually incrementing the playhead one cant do this (meaning the pre-fetching)? So is the timebase 'just in time' decoding? and this is what QC does?

Is this what you mean by asynchronous vs time based?

Forgive me for being .. um. dense (long day). Feel free to speak to me like im 5 years old (no, im serious, I really am curious and dont mind if you feel like you are patronizing me or anything - id rather know).

Just curious - although ive got the feeling Ive answered my own question here.

Ive cc'ed the QC list for their amusement.

On Jul 13, 2007, at 7:49 PM, Pierre-Olivier Latour wrote:

Here's an analogy: open a movie in QT Player, then play it:
1 - either by press right arrow key repetitively, or dragging the playhead, etc...
2 - either by pressing play

QC does #1 for reasons explained before and for some codecs, some movie sizes and a whole bunch of factors, this may not be as efficient as #2

On Jul 13, 2007, at 4:40 PM, Roger Bolton wrote:

On 14 Jul 2007, at 00:31, Pierre-Olivier Latour wrote:

There's no doc that I know of or anything: it's just common sense: if the movie is stepped frame-by-frame like QC does because it tracks the patch time, it's just less efficient as playing it straight in a "continuous" way which allows pre-fetching of the data, async decompression and whatnot.

I'm not really understanding you here. Quicktime also tracks timecode and plays frame by frame, otherwise it would play faster than realtime and lose sync. The whole point of quicktime is that a 25 fps clip will never play faster than 25fps. Quicktime also needs to keep multiple tracks in sync, eg quicktime can have more than one audio track, so it has to have its own internal counter which is telling it when to play each frame. How is this different to the way that QC handles it?

From my own experience QC can play back HD in realtime and efficiently, I don't really see a performance difference between QC and QT player.

Roger
CoreMelt

v a d e //

www.vade.info

abstrakt.vade.info

_______________________________________________ Do not post admin requests to the list. They will be ignored. Quartzcomposer-dev mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/quartzcomposer-dev/email@hidden This email sent to email@hidden

Follow-Ups:

Re: QuickTime playback jitter
- From: Alessandro Sabatelli <email@hidden>

References:

>Re: QuickTime playback jitter (From: "Johnson, Mark P. - Duluth" <email@hidden>)

>Re: QuickTime playback jitter (From: Pierre-Olivier Latour <email@hidden>)

>Re: QuickTime playback jitter (From: vade <email@hidden>)

>Re: QuickTime playback jitter (From: Pierre-Olivier Latour <email@hidden>)

>Re: QuickTime playback jitter (From: Roger Bolton <email@hidden>)

>Re: QuickTime playback jitter (From: Pierre-Olivier Latour <email@hidden>)