LEAD MPEG-4 Encoder/Decoder

The LEAD MPEG-4 Encoder/Decoder is a DirectShowÒ filter for compressing/decompressing video data using the MPEG-4 (ISO/IEC 14496-2) standard. MPEG-4 is suitable for a wide range of bandwidths from low bandwidth to broadband. In addition to MP4 files, MPEG4 compressed video data can be stored inside AVI or OGG files with the option of saving the file with or without the audio data.

Key Features:

LEAD's MPEG-4 video codec is a multimedia compressor / decompressor that registers into the Windows® collection of multimedia drivers and integrates with any application using DirectShow. Existing video software, such as Windows® Media Player® and Ulead Media Studio®, can utilize this codec to play, create and edit industry standard (ISO/IEC 14496-2) MPEG-4 streams.

User Interface:

Options for the LEAD MPEG-4 Encoder can be set manually through the encoder property page, which is shown in the following figure:

Changes will be applied only when filter’s state is stopped with the ability to set them permanently by clicking Apply or OK, or to abandon changes by clicking Cancel. Positioning the mouse pointer over a control displays general information for that control.

If you are using the encoder with a third-party software package, refer to your software’s documentation for information on how to access the encoder’s property page(s).

The following table shows the controls and their descriptions:

Control

Description

Compression Group

Quality Factor drop-down list box

The desired quality factor. The lower the quality factor, the better the quality. Possible values range from 1 (best) to 31 (worst).

Quantization type drop-down list box

The type of quantization to be used. Possible values are:

 

Value

Meaning

 

Linear

Use H.263 quantization.

 

Non-linear

Use MPEG quantization.

Output group

Frame rate drop-down list box

The desired output frame rate, in frames per second. Possible values are:

 

Value

Meaning

 

Input Frame Rate

Make the output frame rate the same as the input frame rate.

 

A value from 1.0 to 30.0

Use the specified output frame rate in frames per second.

Format drop-down list box

The encoder output type.  Selecting the LEAD proprietary subtype, LMP4, enables the usage of super compression. Possible values are:

 

Value

Meaning

 

mp4v

Make the encoder output type the Standard MPEG4 video media subtype.

 

LMP4

Make the encoder output type the LEAD proprietary MPEG4 video subtype. This allows super compression to be used.

Super Compression check box

Enables/disables super compression. This is valid only with the LMP4 output type (format). 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.

Group Of Pictures group

No. of Ps between 2 Is drop-down list box

The number of P frames between two successive I frames *.

No. of Bs between 2 Ps drop-down list box

The number of B frames between two successive P frames *.

Group Of Picture size static text

The expected output GOP size.

 

Motion Estimation group

Search option drop-down list box

Predefined values for the dimensions of the search block used when determining if motion is occurring. Selecting “Custom” enables the Search Width and Search Height spin edit boxes and is selected by default. Possible values are:

 

Value

Meaning

 

Fast

(8x8)

 

Normal

(16x16)

 

Slow

(24x24)

 

Very Slow

(32x32)

 

Custom

width 16 height 16

Search width spin box

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.

Search height spin box

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.

Motion algorithm drop-down list box

The algorithm to be used when determining if motion is occurring. Possible values are:

 

Value

Meaning

 

Full Search

Use the full motion search algorithm (testing all possibilities). This option slows down the encoding process considerably.

 

Fast Search

Use fast motion search.

Four vector motion check box

If selected, the encoder will use four vectors in the motion estimation algorithm. Otherwise, one motion vector is used. When 4 vectors are used the quality is better, but the encoding is slower.

Half pixel motion check box

If selected, the encoder will use Half-Pixel accuracy (faster encoding); Full-Pixel accuracy is used otherwise.

 

* 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, which are described as follows:

I: (Intraframe) frames, also called Key Frames, 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 the 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 from both 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 the “No. of Ps between 2 Is” and the No. of Bs between 2 Ps.