Media Foundation Frames in Byte Format Run-Time - ms-media-foundation

Question

I use media foundation to capture alive webcam video, is it possible to get the frames captured in a byte streams format in Run-Time and to write them as a stream of bits in a text file after each time cycle ?
I am not sure that I can have the stream in byte format(without container) neither I can do that on run time?

Answer 1

It's not completely clear what you're asking. If you want to capture the raw frames from webcam and save them to a file then the answer is yes that can be done. The Media Foundation SDK MFCaptureToFile sample does exactly that although because it uses a SinkWriter you will have to specify a container file type such as mp4 when creating it.
If you really do want to get the raw frames one by one then you need to dispense with the SinkWriter (or write a custom one). Below is a code snippet that shows getting samples from an IMFSourceReader and converting them into a byte array (and a few other things). You could write the byte array to a text file although unless you do something like put a bitmap header on it it won't be very useful. The IMFSourceReader, IMFMediaTypes all need to be set up correctly prior to being able to call ReadSample but hopefully it gives you a rough idea of where to look further.
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;
}
}
}