字节格式的媒体基础帧运行-Time

Question

我使用 media foundation 来捕获实时网络摄像头视频，是否可以在 运行-Time 中获取以字节流格式捕获的帧并写入它们作为每个时间周期后文本文件中的比特流？

我不确定我能否拥有字节格式的流（没有容器），我也不能在运行时间做到这一点？

Answer 1

你问的不是很清楚。如果您想从网络摄像头捕获原始帧并将它们保存到文件中，那么答案是肯定的，可以做到。媒体基础 SDK MFCaptureToFile 示例正是这样做的，尽管因为它使用 SinkWriter，您在创建它时必须指定容器文件类型，例如 mp4。

如果你真的想一个一个地获取原始帧，那么你需要放弃 SinkWriter（或编写一个自定义的）。下面是一个代码片段，显示从 IMFSourceReader 获取样本并将它们转换为字节数组（以及其他一些东西）。您可以将字节数组写入文本文件，但除非您执行类似在其上放置位图 header 之类的操作，否则它不会很有用。 IMFSourceReader、IMFMediaTypes 都需要在能够调用 ReadSample 之前正确设置，但希望它能让您大致了解在哪里可以进一步查看。

HRESULT MFVideoSampler::GetSample(/* out */ array<Byte> ^% buffer)
{
    if (_videoReader == NULL) {
        return -1;
    }
    else {
        IMFSample *videoSample = NULL;
        DWORD streamIndex, flags;
        LONGLONG llVideoTimeStamp;

        // Initial read results in a null pSample??
        CHECK_HR(_videoReader->ReadSample(
            //MF_SOURCE_READER_ANY_STREAM,    // Stream index.
            MF_SOURCE_READER_FIRST_VIDEO_STREAM,
            0,                              // Flags.
            &streamIndex,                   // Receives the actual stream index. 
            &flags,                         // Receives status flags.
            &llVideoTimeStamp,                   // Receives the time stamp.
            &videoSample                        // Receives the sample or NULL.
            ), L"Error reading video sample.");

        if (flags & MF_SOURCE_READERF_ENDOFSTREAM)
        {
            wprintf(L"\tEnd of stream\n");
        }
        if (flags & MF_SOURCE_READERF_NEWSTREAM)
        {
            wprintf(L"\tNew stream\n");
        }
        if (flags & MF_SOURCE_READERF_NATIVEMEDIATYPECHANGED)
        {
            wprintf(L"\tNative type changed\n");
        }
        if (flags & MF_SOURCE_READERF_CURRENTMEDIATYPECHANGED)
        {
            wprintf(L"\tCurrent type changed\n");

            IMFMediaType *videoType = NULL;
            CHECK_HR(_videoReader->GetCurrentMediaType(
                (DWORD)MF_SOURCE_READER_FIRST_VIDEO_STREAM,
                &videoType), L"Error retrieving current media type from first video stream.");

            Console::WriteLine(GetMediaTypeDescription(videoType));

            // Get the frame dimensions and stride
            UINT32 nWidth, nHeight;
            MFGetAttributeSize(videoType, MF_MT_FRAME_SIZE, &nWidth, &nHeight);
            _width = nWidth;
            _height = nHeight;

            //LONG lFrameStride;
            //videoType->GetUINT32(MF_MT_DEFAULT_STRIDE, (UINT32*)&lFrameStride);

            videoType->Release();
        }
        if (flags & MF_SOURCE_READERF_STREAMTICK)
        {
            wprintf(L"\tStream tick\n");
        }

        if (!videoSample)
        {
            printf("Failed to get video sample from MF.\n");
        }
        else
        {
            DWORD nCurrBufferCount = 0;
            CHECK_HR(videoSample->GetBufferCount(&nCurrBufferCount), L"Failed to get the buffer count from the video sample.\n");

            IMFMediaBuffer * pMediaBuffer;
            CHECK_HR(videoSample->ConvertToContiguousBuffer(&pMediaBuffer), L"Failed to extract the video sample into a raw buffer.\n");

            DWORD nCurrLen = 0;
            CHECK_HR(pMediaBuffer->GetCurrentLength(&nCurrLen), L"Failed to get the length of the raw buffer holding the video sample.\n");

            byte *imgBuff;
            DWORD buffCurrLen = 0;
            DWORD buffMaxLen = 0;
            pMediaBuffer->Lock(&imgBuff, &buffMaxLen, &buffCurrLen);

            if (Stride != -1 && Stride < 0) {
                // Bitmap needs to be flipped.
                int bmpSize = buffCurrLen; // ToDo: Don't assume RGB/BGR 24.
                int absStride = Stride * -1;
                byte *flipBuf = new byte[bmpSize];

                for (int row = 0; row < _height; row++) {
                    for (int col = 0; col < absStride; col += 3) {
                        flipBuf[row * absStride + col] = imgBuff[((_height - row - 1) * absStride) + col];
                        flipBuf[row * absStride + col + 1] = imgBuff[((_height - row - 1) * absStride) + col + 1];
                        flipBuf[row * absStride + col + 2] = imgBuff[((_height - row - 1) * absStride) + col + 2];
                    }
                }

                buffer = gcnew array<Byte>(buffCurrLen);
                Marshal::Copy((IntPtr)flipBuf, buffer, 0, buffCurrLen);

                delete flipBuf;
            }
            else {
                buffer = gcnew array<Byte>(buffCurrLen);
                Marshal::Copy((IntPtr)imgBuff, buffer, 0, buffCurrLen);
            }

            pMediaBuffer->Unlock();
            pMediaBuffer->Release();

            videoSample->Release();

            return S_OK;
        }
    }
}

字节格式的媒体基础帧运行-Time

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