LEAD H264 Encoder User Interface (4.0)

The Encoder property page provides a user interface for changing the filter attributes.

Changes will be applied only when filter’s state is stopped with the ability to set them permanently by clicking Apply or OK, or abandoning them by clicking Cancel. Positioning the mouse pointer over a control displays the general information for that control. The property page is shown in the following figure:

The following table shows the controls and their descriptions:

Control	Description
Quality Driven radio button	If this button is selected, a quality factor, set in the Quality Factor edit box, determines the video quality. A Quality Factor of 1 gives the highest quality and the largest video file size. A Quality Factor of 49 gives the smallest file size with low video quality. The default is 28.
Quality Factor edit box	Value that determines the video quality if the Quality Driven radio button is selected.
Rate Driven radio button	If this button is selected, the compression level is constant and the storage requirements can be easily predicted. However, the quality of more dynamic scenes or those with more picture detail may be affected. The associated bit rate describes the amount of data used/transferred within a time period. It is directly related to the compression level. The higher the bit rate, the lower the compression and the better the quality. The bit rate can be adjusted using the Bit Rate edit box in Bits Per Sec.
Bit Rate edit box	Value that determines the bit rate if the Rate Driven radio button is selected.
CABAC (Arithmetic Coding) radio button	Sets the entropy coding mode to Context-based Adaptive Binary Arithmetic Coding (CABAC). CABAC gives better compression at the same quality but is a little bit slower than CAVLC.
CAVLC (Huffman) radio button	Sets the entropy coding mode to Context-Adaptive Variable-Length Coding (CAVLC). CABAC gives better compression at the same quality but is a little bit slower than CAVLC.
Output Format drop-down list box	Selects the output format. Possible values are as follows:
	Auto	Have the LEAD H264 LEAD H264 is a DirectShow filter for compressing and decompressing Video data using the H264/AVC standard. H264 is the latest video standard developed jointly by ITUand MPEG. H264/AVC provides a far more efficient algorithm for compressing video.It typically outperforms all existing standards by a factor of three to four especiallyin comparison to MPEG-2. Encoder determine the appropriate format.
	Standard (h264)	Use MEDIASUBTYPE_h264
	Standard (avc1)	Use ISOMEDIATYPE_avc1 or MEDIASUBTYPE_avc1
	LEAD (L264)	Use MEDIASUBTYPE_L264 or MEDIASUBTYPE_LX64
	iPod (avc1)	Use ISOMEDIATYPE_avc1 or MEDIASUBTYPE_avc1 The LEAD H264 Encoder will use the appropriate setting to produce video files that can be played on iPod devices.
	PSP (avc1)	Use ISOMEDIATYPE_avc1 or MEDIASUBTYPE_avc1 The LEAD H264 Encoder will use the appropriate setting to produce video files that can be played on PSP devices.
Super Compression check box	If this check box is selected, LEAD's improvement to the H264 compression is used. Files generated using this option, will not be H264-compliant, and can only be decoded by the LEAD H264 decoder . This option produces very high compression and makes the encoding and decoding processes very fast. If high quality video is desired it is not recommended to use this option, because the output video quality will not be as good as the original. This check box is available when the output format is LEAD (L264).
Output Frame Rate drop-down list box	Sets the playback frame rate, in frames per second, of the compressed video, regardless of the rate of the input stream frames. The LEAD H264 Encoder automatically adjusts the input video to match the desired frame rate. The rate is adjusted by dropping or duplicating input frames. If the selected frame rate is lower than the original frame rate, the compression will be higher. If "input framerate" is selected, the output frame rate will be exactly the same as the input frame rate. Use this selection when you don't want to change the frame rate.
No. of Ps between 2 Is drop-down list box	Sets the number of P frames between 2 successive I frames.
No. of Bs between 2 Ps drop-down list box	Sets the number of B frames between 2 successive P frames.
Encoding Speed drop-down list box	Sets the speed of the encoding based on the motion estimation algorithm option. Possible values are:
	1	Very Fast, suitable for Capturing or Converting
	2	Fast, suitable for Capturing or Converting
	3	Slow, suitable for Converting
	4	Very Slow, suitable for Converting only
	Option 4 gives the highest compression while Option 3 gives the second highest compression. Option 1 gives the smallest compression while Option 2 gives slightly better compression than Option 1 but less than Option 3.
Encoding Threads drop-down list box	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:
	Auto	Have the LEAD H264 Encoder determine the appropriate number of threads.
	1	Use 1 thread during encoding
	2	Use 2 threads during encoding
Time Quality Factor File edit box	Sets the name of the file that has a set of time stamps and the desired quality factors to be used by the encoder. To create such a file just open a regular text file and start writing the time stamps and each corresponding quality factor. The format of the time stamps and quality factor should appears as follows: #00:00:00:000-00:00:01:000 26 #00:00:02:000-00:01:03:000 40 The above two lines mean: between 0 seconds and one second, use Quality Factor of 26. between 1 second and 2 seconds, use the default Quality Factor. between 2 seconds and 1 minute and 3 seconds, use Quality Factor of 40. You can put as many time stamps-quality factors as needed. They must be within the video clip time span to be considered by the encoder.

I Frames and P Frames

To increase the compression performance, H264 uses Temporal Compression. Temporal compression is achieved by encoding only 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 H264 video stream The portion of the file holding the video data. The video data might be compressed to save disk space. The data has to be decompressed using a video decompressor before you can play (see) it. comprises I Frames, B Frames and P Frames:

I: (Intraframe) frames. These are encoded without reference to another frame to allow for random access.
P: (Predictive) frames are encoded using the previous I (or P) frame as reference. P frames are compressed more than I frames.
B: (Bi-directional) frames are encoded using both previous and next I (or P) frames as reference and they are compressed more than both I, and P frames.

To increase the compression of H264, more B and P frames should be used. You do so using the "No. of Ps between 2 Is" and "No. of Bs between 2 Ps" options on the Encoder Property Page:

No. of Ps between 2 Is: represents the number of P frames between 2 successive I frames. All the frames between successive I frames are P or B frames.
No. of Bs between 2 Ps: represents the number of B frames between 2 successive P frames. All the frames between successive P frames are B frames.

For example if No. of Ps between 2 Is is 3, and No. of Bs between 2 Ps is 5, then the video stream looks like:

I B B B B B P B B B B B P B B B B B P &..

The distance between I frames must be a multiple of the distance between the P frames. The encoder will automatically adjust these values to preserve this relationship.