UWP, Media Foundation, choosing specific encoder - c++

Question

I would like to choose a specific encoder in Media Foundation under UWP using c++/cx. Currently I use a SinkWriter and let the system choose a default encoder.
This code returns "class not registered" error under UWP, but it works in a win32 console app:
CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);
MFStartup(MF_VERSION);
IMFTransform* mtf;
CLSID id;
CLSIDFromString(L"{966F107C-8EA2-425D-B822-E4A71BEF01D7}", &id); // "NVIDIA HEVC Encoder MFT"
//CLSIDFromString(L"{F2F84074-8BCA-40BD-9159-E880F673DD3B}", &id); // "H265 Encoder MFT"
//CLSIDFromString(L"{BC10864D-2B34-408F-912A-102B1B867B6C}", &id); // "Intel« Hardware H265 Encoder MFT"
//HRESULT hr = CoCreateInstance(id, nullptr, CLSCTX_INPROC_SERVER, IID_IMFTransform, (void **)&mtf);
HRESULT hr = CoCreateInstance(id, nullptr, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&mtf));
I also noticed that MFTEnumEx() is not definded in the header files under UWP, so I can't enumerate the encoders.
I noticed there is C# documentation allowing something like this:
auto codecQuery = ref new Windows::Media::Core::CodecQuery();
But it seems it not available when using c++/cx.
I would also like to ask the SinkWriter what encoder it actually chose, but this code does not work because ICodecAPI is undefined:
IMFTransform* pEncoder = NULL;
mWriter->GetServiceForStream(MF_SOURCE_READER_FIRST_VIDEO_STREAM, GUID_NULL, IID_IMFTransform, (void**)&pEncoder);
if (pEncoder)
{
ICodecAPI* pCodecApi = NULL;
hr = pEncoder->QueryInterface<ICodecAPI>(&pCodecApi);
}
Please help me choose encoder or find out which encoder was chosen?

Answer 1

Media Foundation does not offer flexibility to specify encoder using Sink Writer API. You can only instruct to use or not use hardware encoder, using MF_READWRITE_ENABLE_HARDWARE_TRANSFORMS attribute:
Enables the source reader or sink writer to use hardware-based Media Foundation transforms (MFTs).
Once Sink Writer is set up, you can use IMFSinkWriterEx::GetTransformForStream to enumerate the transforms the API prepared for the processing and pick the encoder from the enumeration. This is going to give you an idea what encoder is actually used.
Media Foundation Sink Writer API reserves the right to decode which encoder to use. Typically if would prefer certified compatible encoder, especially if you enable Direct3D scenario.
Finally, I am not sure which of these is available for C++/CX, but your code snippets suggest that the mentioned API is available.
To use encoder of your choice, you are supposed to use Media Foundation Media Session API, as opposed to Sink Writer.

Answer 2

Thank you Roman. I tried GetTranformForStream. With nvidia driver I get the attributes for the IMFTransform:
{206B4FC8-FCF9-4C51-AFE3-9764369E33A0}=1,
{2FB866AC-B078-4942-AB6C-003D05CDA674}=NVIDIA HEVC Encoder MFT,
FRIENDLY_NAME_Attribute=NVIDIA HEVC Encoder MFT,
{3AECB0CC-035B-4BCC-8185-2B8D551EF3AF}=VEN_10DE,
MAJOR_TYPE=Video,
{53476A11-3F13-49FB-AC42-EE2733C96741}=1,
{86A355AE-3A77-4EC4-9F31-01149A4E92DE}=1,
{88A7CB15-7B07-4A34-9128-E64C6703C4D3}=8,
{E3F2E203-D445-4B8C-9211-AE390D3BA017}=2303214,
{E5666D6B-3422-4EB6-A421-DA7DB1F8E207}=1,
{F34B9093-05E0-4B16-993D-3E2A2CDE6AD3}=860522,
SUBTYPE=Base,
{F81A699A-649A-497D-8C73-29F8FED6AD7A}=1,
When disabling nvidia driver I only get:
{86A355AE-3A77-4EC4-9F31-01149A4E92DE}=1
I wonder if the last transform is a list of several transforms? How to get them? Can I traverse the topology from sinkwriter?
My pc has the following codecs I could use:
{966F107C-8EA2-425D-B822-E4A71BEF01D7} // "NVIDIA HEVC Encoder MFT"
{F2F84074-8BCA-40BD-9159-E880F673DD3B} // "H265 Encoder MFT"
{BC10864D-2B34-408F-912A-102B1B867B6C} // "Intel« Hardware H265 Encoder MFT"
In the nvidia case, I get a meaningful string, but not when it is not nvidia apparently (Intel or software).
Now I will also try look into Media Session API as you suggested.