MFSampleExtension_Encryption_ProtectionScheme attribute

Specifies the protection scheme for encrypted samples.

Data type

UINT32

Remarks

The value of this attribute is a member of the MFSampleEncryptionProtectionScheme enumeration. In cases where the media source is MP4-based, the value is set based off the value of the scheme_type field within the scheme type box (‘schm’) in the MP4 header (‘moov’ or ‘moof’).

If the scheme_type field in an MP4-based file, or stream, is set to ‘cenc’ or ‘cbc1’, then the MFSampleExtension_Encryption_ProtectionScheme attribute should be set to PROTECTION_SCHEME_AES_CTR or PROTECTION_SCHEME_CBC, respectively, and no values should be set for MFSampleExtension_Encryption_CryptByteBlock and MFSampleExtension_Encryption_SkipByteBlock.

If the scheme_type field in an MP4-based file, or stream, is set to ‘cens’ or ‘cbcs’, then the MFSampleExtension_Encryption_ProtectionScheme attribute should be set to PROTECTION_SCHEME_AES_CTR or PROTECTION_SCHEME_CBC, respectively, and MFSampleExtension_Encryption_CryptByteBlock and MFSampleExtension_Encryption_SkipByteBlock must be set using the values in the ‘tenc’ box.

Examples

The following example shows how to set the MFSampleExtension_Encryption_ProtectionScheme and the associated MFSampleExtension_Encryption_CryptByteBlock and MFSampleExtension_Encryption_SkipByteBlock attributes.

HRESULT AddEncryptionAttributes(_In_ IMFSample* pSample, _In_ bool fIsEncrypted)
{
 HRESULT hr = S_OK;

 if (fIsEncrypted)
 {
 //Set Encryption Protection Scheme
 hr = pSample->UINT32(MFSampleExtension_Encryption_ProtectionScheme,
 SAMPLE_ENCRYPTION_PROTECTION_SCHEME_AES_CBC);
 if (FAILED(hr))
 return hr;

 //Set the Initialization Vector (IV)
 //(spSampleEncryptionData is omitted from this example for simplicity.) 
 hr = pSample->SetBlob(MFSampleExtension_Encryption_SampleID, 
 (BYTE*)(spSampleEncryptionData->m_pInitializationVector),
 spSampleEncryptionData->m_bIVSize);
 if (FAILED(hr))
 return hr;

 //Set crypt and skip byte blocks for pattern encryption
 hr = pSample->SetUINT32(MFSampleExtension_Encryption_CryptByteBlock, 1);
 if (FAILED(hr))
 return hr;

 hr = pSample->SetUINT32(MFSampleExtension_Encryption_SkipByteBlock, 9);
 if (FAILED(hr))
 return hr;
 }
 return hr;
}

Requirements