Reliably getting timecodes/stream position   

I would like to be able to reliably access the current timecode from a DV 
stream (from MS VCR and camcorder device). The problem I have with 
IAMTimecodeReader is that it seems to be very delayed. My graph has a custom 
filter which can introduce up to a 5 frame delay between what is being 
captured from the source, and what is being rendered at the other end of the 
graph. Since the custom filter doesn't care about the timecodes, I don't read 
them there and would not like to. The filter is not always connected to a DV 
device anyways. 

If I use IAMTimecodeReader at the end of the graph, the timecode is up to 
5-7 frames out of date due to the length of the graph. Even so, it seems to 
me that if I used IAMTimecodeReader in the custom filter it would still be 
1-2 frames out of sync. 


I have a similar problem when capturing from files. I use 
IMediaSeeking::GetPositions, but this has the same problem of telling the 
position of the source, when the source is delayed by the length of the graph.


Lastly, it is frustrating that there is no standard interface to access 
timecodes regardless of the capture source. Is there a way that will work to 
access timecodes if they are available, no matter what the source?

date: Thu, 17 Jul 2008 00:37:00 -0700   author:   Bob

Re: Reliably getting timecodes/stream position   

On Jul 17, 9:37 am, Bob  wrote:
> I would like to be able to reliably access the current timecode from a DV
> stream (from MS VCR and camcorder device). The problem I have with
> IAMTimecodeReader is that it seems to be very delayed. My graph has a custom
> filter which can introduce up to a 5 frame delay between what is being
> captured from the source, and what is being rendered at the other end of the
> graph. Since the custom filter doesn't care about the timecodes, I don't read
> them there and would not like to. The filter is not always connected to a DV
> device anyways.
>
> If I use IAMTimecodeReader at the end of the graph, the timecode is up to
> 5-7 frames out of date due to the length of the graph. Even so, it seems to
> me that if I used IAMTimecodeReader in the custom filter it would still be
> 1-2 frames out of sync.
>
> I have a similar problem when capturing from files. I use
> IMediaSeeking::GetPositions, but this has the same problem of telling the
> position of the source, when the source is delayed by the length of the graph.

> Lastly, it is frustrating that there is no standard interface to access
> timecodes regardless of the capture source. Is there a way that will work to
> access timecodes if they are available, no matter what the source?
NO
What is bothering you really? The delay itself? or the fact that it is
not the same for different sources?
If you are aiming for frame accurate measurements across the board, I
think you will have to implement your own solution.

date: Thu, 17 Jul 2008 09:18:00 -0700 (PDT)   author:   Michel Roujansky - Senior developer, Starfish Technologies Ltd