Audio/video synchronization

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Hi DirectX group!

Im working on writing an application that can send out video and audio
to a Black magic output card.

We have a stack of frames and a stack of frames and a stack of audio
samples that matches each other, now we want to send them to our
output card. This is done by using special Push source filters
provided by Black Magic. These filters are the start point in a graph
that sends output to the card:

VIDEO: Video push source -> Inf Pin Tee -> Sample Grabber -> Video
Render Filter

AUDIO: Audio push source -> Sample Grabber -> Audio Render Filter

Both video and audio samples are provided with time stamps that should
be used for sync. When we monitor these timestamps in the sample
grabber they seem to be just as we want them to be.

Our video samples are 1 frame (40 ms with 25 fps) and our audio
samples are 1 sec (1000 ms) each.

The output seems to be working. Only problem is that the audio and
video starts at different times (audio is 0-120 ms delayed). Everytime
we restart the graph the delay is different. From here on the delay
stays the same. Could it be that timestamps are ignored for some
reason?

What could cause this behavior?

Hope to find some answers!

Rasmus
.

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