What does HRESULT 0xC00D4A3C (MF_E_STREAMSINK_EXISTS) mean?

MF_E_STREAMSINK_EXISTS

MF_E_STREAMSINK_EXISTS is returned by dynamic stream creation when the requested stream identifier is already in use. The identifier passed to IMFMediaSink::AddStreamSink is application-selected, but Microsoft requires it to be unique within that media sink.

Track stream identifiers as sink-local keys

• Log the media sink identity and dwStreamSinkIdentifier for every successful and failed add operation.
• Do not reuse an identifier merely because a different topology branch or source stream uses the same numeric ID.
• If a stream was meant to be replaced, remove the old stream sink first and stop using every cached pointer to it.

Changing the media type will not resolve this HRESULT because the collision is detected on the identifier itself. Also distinguish it from MF_E_STREAMSINKS_FIXED, where no identifier would be accepted because the sink does not support adding streams at all.

Microsoft: IMFMediaSink::AddStreamSink · Microsoft: IMFMediaSink · Wine: mferror.h