MNG and Synchronisation

[Martin Plassen]

I have tried to use animated GIFs to solve a specific
programming task in my user interface. However, I am not able to achieve what
at I want with GIFs. The problem is if I put two similar GIFs next to each other,
after some time, they are not any longer synchronised. I need them to be. So my
question is, will animated MNG files behave better in this respect ?
I am working in Win32 environments.
Please reply directly to me also, since I am not receiving this list.
Martin


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[Glenn Randers-Pehrson]

On Tue, Oct 13, 2009 at 2:57 AM, Martin Plassen
<Martin.Plassen@...> wrote:
> I have tried to use animated GIFs to solve a specific
> programming task in my user interface. However, I am not able to achieve what
> at I want with GIFs. The problem is if I put two similar GIFs next to each other,
> after some time, they are not any longer synchronised. I need them to be. So my
> question is, will animated MNG files behave better in this respect ?
> I am working in Win32 environments.
> Please reply directly to me also, since I am not receiving this list.
> Martin
>


That would depend on the player software.  If the GIFs
get out of sync, then MNGs probably will as well.

[I tried to answer you directly last time you asked me
but your mail (at users.sourceforge.net) bounced]

Glenn

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[Willem van Schaik]

But why don't you make the two animated GIFs or MNGs into one large  
one with a transparent piece in the middle. Using the current CSS  
absolute positioning techniques you could still have text or other  
images being on top (or under) that transparent part.

Just my $0.02,
Willem



On 13-Oct-09, at 12:57 AM, Martin Plassen wrote:

> I have tried to use animated GIFs to solve a specific
> programming task in my user interface. However, I am not able to  
> achieve what
> at I want with GIFs. The problem is if I put two similar GIFs next  
> to each other,
> after some time, they are not any longer synchronised. I need them  
> to be. So my
> question is, will animated MNG files behave better in this respect ?
> I am working in Win32 environments.
> Please reply directly to me also, since I am not receiving this list.
> Martin
>
>
> ------------------------------------------------------------------------------
> Come build with us! The BlackBerry(R) Developer Conference in SF, CA
> is the only developer event you need to attend this year. Jumpstart  
> your
> developing skills, take BlackBerry mobile applications to market and  
> stay
> ahead of the curve. Join us from November 9 - 12, 2009. Register now!
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> png-mng-misc mailing list
> png-mng-misc@...
> https://lists.sourceforge.net/lists/listinfo/png-mng-misc

--

Willem van Schaik
willem@...




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[John Bowler]

From: Martin Plassen [mailto:Martin.Plassen@...]
> The problem is if I put two similar GIFs next to each other,
>after some time, they are not any longer synchronised.

Because the GIF file format specifies a delay between frames, and,
typically, a free running animation engine handles errors in the delay by
ignoring them (rather than shortening the delay in the following frame to
catch up.)

There was an extension to IE that allowed the web page to explicitly specify
the frame to move to.  This allowed a script in the page to take over
control of the animation.  That would probably work for you if the animation
engine you have supports a 'go to frame' feature.

Even easier is to get the animation engine changed to use absolute time for
each frame - it's a small, easy, internal change and can easily be added as
an option.

That may still fail if you don't control the GIFs because the GIF
inter-frame delay is specified in centiseconds, so there is an average
round-off error of 0.25cs per frame.  That can easily accumulate over
sufficient frames to give the 0.1s error between two animations that is
noticeable.

>So my  question is, will animated MNG files behave better in this respect ?

I think so.  Certainly these issues were part of the design of MNG, whereas
GIF was not even designed as an animation format.  MNG files have more
accurate frame timing and the "FRAM" chunk specifies the handling of
inter-frame delay more precisely.  The "external-signal" option was intended
to allow the container to force synchronization of a MNG.  My interpretation
of the "deterministic" option is that it means that frames are replaced at a
time equal to the sum of the inter-frame delays of the frame and its
predecessors - i.e. the absolute time option.

If the same option is used on all the frames in the MNG then the net effect
is, as I interpret the options (Glenn or Willem are both much more expert):

1) deterministic: frames will be displayed at absolute times calculated by
summing the delays.
2) decoder-discretion: like GIF, except that the decoder is only permitted
to extend the delay by the timeout on the frame.
3) user-discretion: the GIF user input option, where frame advance only
happens when the user requests it.
4) external-signal: to synchronize a MNG to some external time source, or
event source, like the IE 'goto frame' extension to GIF handling but more
general.

Of course how well these options work depend on the decoder, and decoders
have no absolute requirement to even implement 'external-signal' because
implementation depends on decoder specific capabilities.

John Bowler <jbowler@...>



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