Media Foundation AMR decode

Question

I have a file with .amr extension, and I want to get it's sample rate and number of channels using Microsoft Media Foundation . Further, I want to decode and get the uncompressed data.

I can successfully get those from .aac .mp4 and other file types but not from from a .amr file (or 3.gp file which contains .amr track).

So, for other types I do:

IMFSourceReader *m_pReader;
IMFMediaType *m_pAudioType;

MFCreateSourceReaderFromURL(filePath, NULL, &m_pReader);
m_pReader->SetStreamSelection(MF_SOURCE_READER_ALL_STREAMS, false);
m_pReader->SetStreamSelection(MF_SOURCE_READER_FIRST_AUDIO_STREAM, true);
m_pReader->GetCurrentMediaType(MF_SOURCE_READER_FIRST_AUDIO_STREAM, &m_pAudioType);

UINT32 numChannels,sampleRate;
m_pAudioType->GetUINT32(MF_MT_AUDIO_NUM_CHANNELS, &numChannels);
m_pAudioType->GetUINT32(MF_MT_AUDIO_SAMPLES_PER_SECOND, &sampleRate);

Consider there are no any errors during this code.

For .amr files, some garbage is being written in the numChannels and sampleRate.

Does anyone have experience with this and knows how to recognize and/or get proper channels and sample rate for further decoding?

BTW, Windows Media Player plays this file with no problems.

Thanks in advance.

Answer 1

So I found out that it supports decoding for .amr files not encoding.

Just before we get this properties:

UINT32 numChannels,sampleRate;
m_pAudioType->GetUINT32(MF_MT_AUDIO_NUM_CHANNELS, &numChannels);
m_pAudioType->GetUINT32(MF_MT_AUDIO_SAMPLES_PER_SECOND, &sampleRate);

We have to set a new media type to our Source Reader

m_pAudioType->SetGUID(MF_MT_MAJOR_TYPE, MFMediaType_Audio)
m_pAudioType->SetGUID(MF_MT_SUBTYPE, MFAudioFormat_Float)
m_pReader->SetCurrentMediaType(MF_SOURCE_READER_FIRST_AUDIO_STREAM, NULL, m_pAudioType);