ILMFMP4Encoder Interface

This is the interface for the LEAD MPEG-4 Encoder.

Data Types

eEncodingThreads

typedef enum  
{ 
   LMP4_THREAD_AUTO, 
   LMP4_THREAD_1, 
   LMP4_THREAD_2, 
   LMP4_THREAD_3, 
   LMP4_THREAD_4, 
   LMP4_THREAD_5, 
   LMP4_THREAD_6, 
   LMP4_THREAD_7, 
   LMP4_THREAD_8, 
} eEncodingThreads; 

Lists the possible encoding threads number that can be set on the property EncodingThreads.

eEncodingPassesCount

typedef enum  
{ 
   LMP4_ENCODINGPASSESCOUNT_ONE, 
   LMP4_ENCODINGPASSESCOUNT_TWO, 
} eEncodingPassesCount; 

Lists the possible encoding passes counts.

eCompressionMode

typedef enum  
{ 
   LMP4_COMPRESSIONMODE_ConstantQuality, 
   LMP4_COMPRESSIONMODE_VariableBitrate, 
   LMP4_COMPRESSIONMODE_ConstantBitrate, 
} eCompressionMode; 

Lists the possible values for the compression mode.

eOutputFormat

typedef enum  
{ 
   LMP4_OUTPUTFORMAT_mp4v, 
   LMP4_OUTPUTFORMAT_LMP4, 
   LMP4_OUTPUTFORMAT_XVID, 
   LMP4_OUTPUTFORMAT_iPod, 
} eOutputFormat; 

Lists the possible values for the output format.

eQuantType

typedef enum  
{ 
   LMP4_QUANTTYPE_Linear, 
   LMP4_QUANTTYPE_NonLinear, 
} eQuantType; 

Lists the possible values for the quantization method to be used by the encoder.

eMotionAccuracy

typedef enum  
{ 
   LMP4_MOTIONACCURACY_FullPixel, 
   LMP4_MOTIONACCURACY_HalfPixel, 
} eMotionAccuracy; 

Lists the possible values for the Motion estimation accuracy.

eMotionAlgorithm

typedef enum  
{ 
   LMP4_MOTIONALGORITHM_FullSearch, 
   LMP4_MOTIONALGORITHM_FastSearch, 
} eMotionAlgorithm; 

List the possible values for the motion algorithm. (the algorithm to be used when determining if motion is occurring).

eMotionVectorPerMacroblock

typedef enum  
{ 
   LMP4_MOTIONVECTOR_OnePerMacroblock, 
   LMP4_MOTIONVECTOR_FourPerMacroblock, 
} eMotionVectorPerMacroblock; 

List the possible values for the motion vectors (vectors to be used in the motion estimation algorithm).

Interface Properties

long QFactor

The quality factor used in compressing the video stream: the lower the quality factor, the better the quality. Possible values range from 1 (best) to 31 (worst).

eQuantType QuantType

The quantization method applied. Possible values are (members of the eQuantType enumeration):

• LMP4_QUANTTYPE_Linear: Use H.263 quantization.
• LMP4_QUANTTYPE_NonLinear:  Use MPEG quantization.

double OutputFrameRate

The desired output frame rate, in frames per second. Possible values range from 1.0 to 30.0. Pass -1 to make the output frame rate the same as the input frame rate.

eOutputFormat OutputFormat

The encoder output type. Possible values are (members of the eOutputFormat enumeration):

• LMP4_OUTPUTFORMAT_mp4v: Make the encoder output type the Standard MPEG4 video media subtype. 
• LMP4_OUTPUTFORMAT_LMP4: Make the encoder output type the LEAD proprietary MPEG4 video subtype. This allows super compression to be used. 
• LMP4_OUTPUTFORMAT_XVID: Make the encoder output type the XVID video subtype.

VARIANT_BOOL SuperCompression

Enables/disables super compression, LEADs improvement to the MPEG4 video compression. When super compression is used, compressed video size is reduced noticeably with almost the same quality, and the encoding and decoding speed is enhanced.Files generated using this option, will not be MPEG4 compliant: they can be decoded only by the LEAD MPEG4 Video Decoder. Possible values are:

• VARIANT_TRUE :  Enable super compression. This is allowed only if the output format is set to LMP4_OutputFormat_LMP4.
• VARIANT_FALSE:  Disable super compression.

long PFrames

Specifies the number of P frames between two successive I frames *.

long BFrames

Specifies the number of B frames between two successive P frames *.

long SceneChangeThreshold

The threshold that determines a scene change point in a video clip. The encoder calculates this value for every inter-frame being encoded. If the calculated value is greater than threshold then it is a scene-change point and the frame will be encoded as an I-frame. This value should be between 1 and 100 and default is 50, (values between 30-50 gives the best compression result). To turn off this feature Scene Change Detection, should be set to 100.

long SearchWidth

The search block width used when determining if motion is occurring. The larger the block, the slower the encoding process. It is not recommended to use large values. The range is from 2 to the video stream width, in pixels.

long SearchHeight

The search block height used when determining if motion is occurring. The larger the block, the slower the encoding process. It is not recommended to use large values. The range is from 2 to the video stream height, in pixels.

eMotionAlgorithm MotionAlgorithm

The algorithm to be used when determining if motion is occurring. Possible values are (members of the eMotionAlgorithm enumeration):

• LMP4_MOTIONALGORITHM_FullSearch:  Use the full motion search algorithm (testing all possibilities). This option slows down the encoding process considerably.
• LMP4_MOTIONALGORITHM_FastSearch:  Use fast motion search.

eMotionAccuracy MotionAccuracy

Motion estimation accuracy. Possible values are (members of the eMotionAccuracy enumeration):

• LMP4_MOTIONACCURACY_FullPixel:  One pixel accuracy.
• LMP4_MOTIONACCURACY_HalfPixel:  Half pixel accuracy (faster).

eMotionAccuracy MotionAccurancy

Motion estimation accuracy. Possible values are (members of the eMotionAccuracy enumeration):

• LMP4_MOTIONACCURACY_FullPixel:  One pixel accuracy.
• LMP4_MOTIONACCURACY_HalfPixel:  Half pixel accuracy (faster).

eMotionVectorPerMacroblock MotionVectorPerMacroblock

Specifies how many motion vectors are used in the motion estimation algorithm. Possible values are (members of the eMotionVectorPerMacroblock enumeration):

• LMP4_MOTIONVECTOR_OnePerMacroblock:  Use one motion vector (fast).
• LMP4_MOTIONVECTOR_FourPerMacroblock:  Use four motion vectors (better quality, slower encoding).

eEncodingThreads EncodingThreads

The number of threads used during encoding. The maximum number of threads that can be used is 2. Using two threads with a dual core machine or 2 CPUs will increase the encoding speed significantly. Possible values are:

• LMP4_THREAD_AUTO: Have the LEAD MPEG4 Encoder determine the appropriate number of threads.
• LMP4_THREAD_1: Use 1 thread during encodingLMP4_THREAD_2: Use 2 threads during encoding.

VARIANT_BOOL InsertVOL

Set to VARIANT_TRUE to insert a mpeg4 header before each I-frame. This is useful in a video broadcasting where the mpeg4 decoder might start decoding from the middle of the stream.

VARIANT_BOOL Interlacing

Set to VARIANT_TRUE to encode the video as interlaced fields. Otherwise, the video is encoded as frames. The default is VARIANT_FALSE.

VARIANT_BOOL InsertGOV

Set to VARIANT_TRUE to insert an optional header before I frames that indicates to the decoder the timestamp of the I frame and whether it is open/closed GOV. This helps the stream to be randomly seeked in some decoders. However, the LEAD MPEG4 decoder does not require it.

eCompressionMode CompressionMode

Sets the compression mode. Possible values are:

• LMP4_COMPRESSIONMODE_ConstantQuality: Uses the QFactor property value to regulate the image quality.
• LMP4_COMPRESSIONMODE_VariableBitrate: Varies the quality over short durations. However, it will achieve an average rate matching the BitRate property value.
• LMP4_COMPRESSIONMODE_ConstantBitrate: Strictly adheres to the rate specified in the BitRate property.

eEncodingPassesCount EncodingPasses

Specifies the number of encoding passes. Possible values are (members of the eEncodingPassesCount enumeration):

• LMP4_ENCODINGPASSESCOUNT_ONE:  Use 1 pass mode in encoding.
• LMP4_ENCODINGPASSESCOUNT_TWO:  Use 2 passes mode in encoding.

long BitRate

This is the average or constant bitrate used when the CompressionMode is set to LMP4_COMPRESSIONMODE_VariableBitrate or LMP4_COMPRESSIONMODE_ConstantBitrate. The value is in bits per second.

Interface Methods

HRESULT ResetToDefaults()

Description

Reset the MPEG-4 encoder option values to the default values.

Returns

S_OK if connected; otherwise, S_FALSE.

HRESULT WriteToRegistry ()

Description

This method writes all of the encoder settings to the system registry. The next time the encoder is loaded, it retrieves the settings from the registry and applies them.

Returns

S_OK if successful; otherwise, S_FALSE.

I Frames and P Frames

* To increase compression performance, MPEG4 uses Temporal Compression. Temporal compression is achieved by only encoding the difference between successive frames instead of the frames themselves. This means that frames cannot be considered in isolation. A given picture is constructed from the prediction from a previous picture, and may be used to predict the next picture. An MPEG-4 video stream is comprised of I Frames, B Frames and P Frames:

• I: (Intraframe) frames. These frames are also called Key Frames, they are encoded without reference to other frames and can be decoded independent of any other frame, and hence they allow random access. I frames are the largest frames in size and least compressed.

• P: (Predictive) frames are encoded using the previous I / P frame as reference and can only be decoded correctly if the previous I / P is available. P frames are smaller and more compressed than I frames.

• B: (Bi-directional) frames are encoded using information frame the previous *I/*P frame and the next I / P frame and can only be decoded correctly if the previous I / P frame and the next I / P frame are available. B frames are smaller than both P and I frames and they are the most compressed frames.

So to increase the compression of MPEG-4 more B and P frames should be used by adjusting PFrames and BFrames properties.