Re: quartz: Set a default sync source on the filtergraph

[Chris Robinson]

On Friday 14 March 2008 04:25:02 pm Maarten Lankhorst wrote:
> Use the fallback system IReferenceClock, unless the app comes up with
> its own clock.

This doesn't look right. According to MSDN, the clock used when Run is called 
is chosen by the following algorithm:

1- The app called IMediaFilter::SetSyncSource

2- A live filter source is connected to the graph and supports the 
IReferenceClock interface

3- Any filters support IReferenceClock, starting with renderers and 
going "upstream" (following pin connections to the source), and falling back 
to disconnected filters if still nothing. Normally, an audio renderer would 
be selected here.

4- If still nothing, use the system reference clock.


I don't think SetDefaultSyncSource should should just jump right to the system 
clock. As far as I can tell, you need to hold a reference to a clock, and a 
bool saying if it's custom set (as even NULL can be a valid custom override). 
When Run is called, if no custom override is set, it would release the 
current set clock (if any) and check as steps 2, 3, and 4 describe.

So really what the function needs to do is release the current set reference 
clock (if non-NULL), clear a custom-override flag (while SetSyncSource sets 
the custom-override flag and holds a reference for non-NULL filters), and 
check steps 2, 3, and 4. So something like:

SetSyncSource(clock) {
    if(this->ref_clock)
        this->ref_clock->Release();
    this->ref_clock = clock;
    if(clock)
        clock->AddRef();
    this->custom_clock = TRUE;
}
SetDefaultSyncSource() {
    SetSyncSource(NULL);
    this->custom_clock = FALSE;
    ...do steps 2, 3, and 4...
    this->ref_clock = selected_clock;
}
Run() {
    if(!this->custom_clock)
        SetDefaultSyncSource();
    ...run...
}

quartz: Set a default sync source on the filtergraph

[Maarten Lankhorst]

Hi Chris,

2008/3/14, Chris Robinson <chris.kcat(a)gmail.com>:
> On Friday 14 March 2008 04:25:02 pm Maarten Lankhorst wrote:
> > Use the fallback system IReferenceClock, unless the app comes up with
> > its own clock.
>
> This doesn't look right. According to MSDN, the clock used when Run is called
>  is chosen by the following algorithm:
>
> 1- The app called IMediaFilter::SetSyncSource
>
> 2- A live filter source is connected to the graph and supports the
>  IReferenceClock interface
>
> 3- Any filters support IReferenceClock, starting with renderers and
>  going "upstream" (following pin connections to the source), and falling back
>  to disconnected filters if still nothing. Normally, an audio renderer would
>  be selected here.
>
> 4- If still nothing, use the system reference clock.
> Almost right.

You're specifying behavior when doing 'run'.

Quoting msdn on IFilterGraph::SetSyncSource:
"This method instructs the Filter Graph Manager to choose a reference
clock using its default algorithm. For more information about the
algorithm that it uses, see Reference Clocks."

There are also strict criteria for live filter sources (basically
webcams or microphones), and when a ireferenceclock will be used from
audio. It needs to expose some interfaces before it is chosen as
reference clock. This patch sets the reference clock to the system
clock, unless overridden by the application. When SetDefaultSyncSource
is called the clock is reset to the system clock.

This isn't entirely conforming, but it's the best solution at the moment.

Cheers,
Maarten.