We are  using Avid DNxHD Codec for decoding DNnHD content.Right now
We want to detect color space information for the encoded DNxHD Stream.
I have found out there is no API mentioned in SDK manual for fetching the
same information.
Is there any way for the decoder to fetch this specific information ?

Apart from that I have an observation that for MOV files containing DNxHD , there are
three boxes silently being written for those.'ACLR' , ARES and APRG. As per the information
 on internet ACLR is Avid's specific color box information.A value of 1 for ACLR box represents
709 and 0 represents RGB. Is this interpretation correct ? Can we rely on this information ?

Atlast one more clarification, in case the stream is encoded in RGB color space, and if I want
to fetch the information in same color space, Do I need to set the m_colorSpace of UncompressedInfo
structure to CS_RGB ?

From operation experience I'd say you can't rely on any flagging re color space. Sadly too many other proccesses get it wrong for it to be reliable.

Vijeta,

ACLR atom is used to set how colorspace transforms RGB<->YCbCr_709 are performed by setting color mapping of the RGB colorspace described by the following structure:

struct colorMappingTypeExtension {

    UInt32  idSize;        // 24

    OSType  extensionType; // 'ACLR'

    OSType  id;            // 'ACLR'

    UInt32  version;       // '0001'

    // 1: CCIR (supercolors will be dropped, 16 will be displayed as black)

    // 2: FullRange (0 will be displayed as black, 16 will be displayed as dark grey)

    UInt32  decodeColorMapping;

    UInt32  reserved;       // must be 0

};

This information wasn't officially published, but it is open. Be aware, that value 0 of the decodeColorMappping field is invalid.

About second question. DNx444 stores RGB encoded data, while all other DNx compressions store YCbCr. With DNxSDK you can obtain uncompressed video in any colorspace. To do so you need to set m_colorSpace value to the desired colr sapce and set a valid m_colorComponentOrder.