IMFSinkWriter quit working

My code used to output a large .mp4 file (e.g. 4MB) that I could successfully play in WMF12.  Since the last time I tested this feature, however, the file being produced is only 677 bytes and WMF12 complains "... might not support the file type ... or codec ...".

I'm pasting a reduced collection of statements from my code that are being executed.  I've traced with breakpoints and every step is happening.  The return result is S_OK every time, including the WriteSample() call.  Yet it seems samples are NOT begin written to the file.

I've included below the output from my own TraceAttributes() function as well.  I believe I was indeed using a combination of pType2 and pType, as the code shows.  I did try changing the AddStream to use pType rather than pType2, but doing so caused the SewtInputMediaType to return 0xC00D5212 (... no codec ...)

This is at the limit of my understanding of Media Foundation.  What might be the reason it doesn't work?  And remember, it used to work, although I can't say for sure what code elements might have changed a little since then.

IMFSinkWriter           *m_pWriterProcessedImage;
			........................................
			hr = MFCreateSinkWriterFromURL(
				FILENAME,
				NULL,
				NULL,&m_pWriterProcessedImage
				);

			.......................................

			hr = m_pWriterProcessedImage->AddStream(pType2, psink_stream);
			hr = m_pWriterProcessedImage->SetInputMediaType(*psink_stream, pType, NULL);
			hr = m_pWriterProcessedImage->BeginWriting();
			TraceAttributes("for AddStream()", pType2);
				**BEGIN OUTPUT FROM TraceAttributes**
					STREAM ATTRIBUTES: for AddStream()
						Type				= {73646976-0000-0010-8000-00AA00389B71}
						Subtype				= {34363248-0000-0010-8000-00AA00389B71}
						bitrate				= 2400000
						size				= 640 x 480
						frame rate			= 30.000000 (30000/1000)
						pixel aspect		= (1/1)
						interlace			= 2 (progressive)
						{AD76A80B-2D5C-4E0B-B375-64E520137036}: <UNRECOGNIZED>
						{3C036DE7-3AD0-4C9E-9216-EE6D6AC21CB3}: <UNRECOGNIZED>
						{261E9D83-9529-4B8F-A111-8B9C950A81A9}: <UNRECOGNIZED>
						{9AA7E155-B64A-4C1D-A500-455D600B6560}: <UNRECOGNIZED>
				**END OUTPUT FROM TraceAttributes**
			TraceAttributes("for SetInputMediaType()", pType);
				**BEGIN OUTPUT FROM TraceAttributes**
						STREAM ATTRIBUTES: for SetInputMediaType()
							Type				= {73646976-0000-0010-8000-00AA00389B71}
							Subtype				= {3231564E-0000-0010-8000-00AA00389B71}
							bitrate				= 15373949
							size				= 640 x 480
							frame rate			= 30.000000 (30000/1000)
							pixel aspect		= (1/1)
							interlace			= 2 (progressive)
							stride				= 640
							independent samples	= 1
							fixed size samples	= 1
							sample size			= 460800
							user data			= 460800
				**END OUTPUT FROM TraceAttributes**
			......................................
			hr = m_pWriterProcessedImage->WriteSample(0, pSample); **THIS GETS CALLED MULTIPLE TIMES**

			........................................
			
			hr = m_pWriterProcessedImage->Finalize();