Using IMFSinkWriter and IMFSourceReader, how to store custom timestamp or tag with each frame as metadata?

Hello,

I need to store a custom timestamp per frame when encoding frames using IMFSinkWriter, to be later read in as attributes from the sample using IMFSourceReader. This is using the H264 encoder and Windows 8.

If not possible is there a sample ID, or any unique value that exists during encoding that can be read in later when decoding?

If this isn't possible, seems like an obvious way to extend the API in Windows 9, after all APIs is the reason why Windows still matters.

Thanks.