Implement 'IMFTransform' to encode or decode H264 or AAC

Question

IMFTransform可以实现IMFTransform接口以对H264或AAC数据进行编码或解码，还是应该使用FFmpeg或OpenH264 ？

Answer 1

When you encode or decode media, IMFTransform is the interface codecs expose in Media Foundation API. That is, you don't implement it - you take advantage of existing implementation of codecs which are available to you (you implement it when you want to extend the API and supply additional codec).

Stock Windows provides you with:

• AAC Decoder - CLSID_CMSAACDecMFT
• AAC Encoder - CLSID_AACMFTEncoder
• H.264 Video Decoder - CLSID_CMSH264DecoderMFT , leverages DXVA hardware-assisted decoding wherever applicable
• H.264 Video Encoder - CLSID_CMSH264EncoderMFT , software (fallback) encoder

Additional hardware accelerated encoders might be provided with hardware drivers. All mentioned above are available in the form of IMFTransform , can be consumed directly or using higher level Media Foundation APIs.

Answer 2

You can implement the IMFTransform interface to decode and encode H264 and AAC. Refer to CLSID_CMSH264DecoderMFT and CLSID_CMSAACDecMFT to decode H264 and ACC, also CLSID_CMSH264EncoderMFT and CLSID_AACMFTEncoder to encode H264 and ACC.

Encoder example : initialise the encoder.

        IUnknown    *_transformUnk;
        IMFTransform *_encoder;

        HRESULT MediaEncoder::InitialiseEncoder(EncoderType encoder)
        {
            HRESULT hr = S_OK;

            // Has the encoder been init.
            if (!_isOpen)
            {
                _encoderType = encoder;

                // Init the COM.
                CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);

                // Create a new close event handler.
                _hCloseEvent = CreateEvent(NULL, FALSE, FALSE, NULL);

                // If event was not created.
                if (_hCloseEvent == NULL)
                {
                    // Get the result value.
                    hr = __HRESULT_FROM_WIN32(GetLastError());
                }

                // If successful creation of the close event.
                if (SUCCEEDED(hr))
                {
                    // Start up Media Foundation platform.
                    hr = MFStartup(MF_VERSION);
                    _isOpen = true;
                }

                if (SUCCEEDED(hr))
                {
                    // Select the encoder.
                    switch (encoder)
                    {
                    case Nequeo::Media::Foundation::EncoderType::H264:
                        // Create the H264 encoder.
                        hr = CreateEncoder(CLSID_CMSH264EncoderMFT);
                        break;

                    case Nequeo::Media::Foundation::EncoderType::AAC:
                        // Create the AAC encoder.
                        hr = CreateEncoder(CLSID_AACMFTEncoder);
                        break;

                    case Nequeo::Media::Foundation::EncoderType::MP3:
                        // Create the MP3 encoder.
                        hr = CreateEncoder(CLSID_MP3ACMCodecWrapper);
                        break;

                    default:
                        hr = ((HRESULT)-1L);
                        break;
                    }
                }

                if (SUCCEEDED(hr))
                {
                    // Query for the IMFTransform interface 
                    hr = _transformUnk->QueryInterface(IID_PPV_ARGS(&_encoder));

                    // Encoder has been created.
                    _created = true;
                }
            }

            // Return the result.
            return hr;
        }

        HRESULT MediaEncoder::CreateEncoder(const CLSID encoder)
        {
            HRESULT hr = S_OK;

            // Create the decoder.
            hr = CoCreateInstance(encoder, NULL, CLSCTX_INPROC_SERVER, IID_IUnknown, (void**)&_transformUnk);

            // Return the result.
            return hr;
        }

Decoder example : initialise the decoder.

    IUnknown    *_transformUnk;
    IMFTransform    *_decoder;

    HRESULT MediaDecoder::InitialiseDecoder(DecoderType decoder)
        {
            HRESULT hr = S_OK;

            // Has the decoder been init.
            if (!_isOpen)
            {
                _decoderType = decoder;

                // Init the COM.
                CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);

                // Create a new close event handler.
                _hCloseEvent = CreateEvent(NULL, FALSE, FALSE, NULL);

                // If event was not created.
                if (_hCloseEvent == NULL)
                {
                    // Get the result value.
                    hr = __HRESULT_FROM_WIN32(GetLastError());
                }

                // If successful creation of the close event.
                if (SUCCEEDED(hr))
                {
                    // Start up Media Foundation platform.
                    hr = MFStartup(MF_VERSION);
                    _isOpen = true;
                }

                if (SUCCEEDED(hr))
                {
                    // Select the decoder.
                    switch (decoder)
                    {
                    case Nequeo::Media::Foundation::DecoderType::H264:
                        // Create the H264 decoder.
                        hr = CreateDecoder(CLSID_CMSH264DecoderMFT);
                        break;

                    case Nequeo::Media::Foundation::DecoderType::AAC:
                        // Create the AAC decoder.
                        hr = CreateDecoder(CLSID_CMSAACDecMFT);
                        break;

                    case Nequeo::Media::Foundation::DecoderType::MP3:
                        // Create the MP3 decoder.
                        hr = CreateDecoder(CLSID_CMP3DecMediaObject);
                        break;

                    case Nequeo::Media::Foundation::DecoderType::MPEG4:
                        // Create the MPEG4 decoder.
                        hr = CreateDecoder(CLSID_CMpeg4sDecMFT);
                        break;

                    default:
                        hr = ((HRESULT)-1L);
                        break;
                    }
                }

                if (SUCCEEDED(hr))
                {
                    // Query for the IMFTransform interface 
                    hr = _transformUnk->QueryInterface(IID_PPV_ARGS(&_decoder));

                    // Decoder has been created.
                    _created = true;
                }
            }

            // Return the result.
            return hr;
        }

        HRESULT MediaDecoder::CreateDecoder(const CLSID decoder)
        {
            HRESULT hr = S_OK;

            // Create the decoder.
            hr = CoCreateInstance(decoder, NULL, CLSCTX_INPROC_SERVER, IID_IUnknown, (void**)&_transformUnk);

            // Return the result.
            return hr;
        }