ILMMP42Encoder

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 passses 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:

Interface Methods:

HRESULT ResetToDefaults();

Description

Resets the filter properties to their default values. Calling this method can cause the filter to reconnect its output pin.

The default values are:
OutputFrameRate = -1.0
PFrames = 9
BFrames = 0
OutputFormat = LMP4_OUTPUTFORMAT_mp4v
BitRate = 300000
interlaced = VARIANT_FALSE
InsertVOL = VARIANT_TRUE
insertGOV = VARIANT_FALSE
SceneChangeThreshold = 50
EncodingPassesCount = LMP4_ENCODINGPASSESCOUNT_ONE
EncodingThreads = LMP4_THREAD_1
CompressionMode = LMP4_COMPRESSIONMODE_ConstantQuality;
MotionVectorPerMacroblock = LMP4_MOTIONVECTOR_OnePerMacroblock;
MotionAccuracy = LMP4_MOTIONACCURACY_FullPixel;
MotionAlgorithm = LMP4_MOTIONALGORITHM_FastSearch;
QuantType = LMP4_QUANTTYPE_Linear;
QFactor = 4;
SuperCompression = 0;
SearchHeight = 16;
SearchWidth = 16;

Returns

S_OK if successful, < 0 if an error occurred.

Common error codes:

HRESULT WriteToRegistry();

Description

Writes the values of all of the properties listed above to the system registry, so that the decoder will remember these settings the next time it is used. This method is automatically called by the property page when you apply modified settings by clicking on the Apply or OK button.

Returns

S_OK if successful, < 0 if an error occurred.

* 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.