LEAD H263 Encoder User Interface (2.0)

The compression options for the LEAD H.263 Encoder can be set manually through the encoder property page. They can also be set programmatically through the ILMH263Encoder interface (see ILMH263Codec Interface).The following figure shows the encoder property page:

Changes will be applied directly to the streaming media 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 softwares documentation for information on how to access the encoders property page(s).

The following table shows the controls and their descriptions:

Compression Group

Use the Compression group controls to manage compression. The LEAD H.263 Encoder has two compression modes: Quality driven, using Variable Bitrate (VBR); and Rate driven, using Constant Bitrate (CBR).

Quality-Driven

Use a variable bitrate to create a file with a specific quality. In such cases, it is not possible to accurately predict the generated file size. However, the movie will have the same quality throughout its length.  Also, videos of various sizes (width, height, frame rate) will have a consistent quality when they are compressed using the same quality factor. Of the predefined options, "Perfect quality" results in the best quality while "Highest compression" results in the worst quality. If none of these are suitable, select one of the custom quality factors. When using quality driven compression:

• Low quality factor values will generate better quality videos and lower compression (larger file size)

• High quality factor values will generate lower quality videos and higher compression (smaller file size)

• Variable bitrate (VBR) compression can be controlled in two ways: by selecting one of the predefined compressions, or by selecting a custom quality factor.

Rate-Driven

Use a constant bitrate when the generated file should have a specific bitrate. Typically this is used when a file is put on a  web site and  the file is to be played by computers whose Internet connection matches a specific speed. Or, when a codec in a videoconferencing application uses a specific connection speed.

Remember that the bitrate is measured in bits per second (bps) not bytes per second! To convert bits/second to bytes/second, divide by 8. Files compressed with variable bitrates should have the same size, regardless of the video width and height. This means that when  two videos of different width and height are converted to the same bitrate, the video with the larger size will have a poorer quality than the video with smaller size.

Constant Bitrate (CBR) compression can be controlled in two ways: by selecting one of the predefined bitrates, or by selecting a custom bitrate.

Advanced/Speed Settings group

Use the controls in the Advanced/Speed Settings group to manage four encoder options that affect the compression. The Predefined Speed options lists the 5 most common combinations. Use the Custom Speed options to turn specific options on or off. When using any of these options, be aware that the compression / decompression algorithm becomes more complex, hence the compression / decompression process becomes slower. However, each option improves the performance of the encoder (resulting in better compression and quality).

Frame Rate Settings

Use the controls in the Frame Rate group to modify the frame rate of the file being compressed. Usually, videos are 30fps (30 frames per second). At this frame rate, the human eye perceives moving objects as smooth. Reducing  the frame rate greatly increases the compression. But, as the frame rate is reduced, the video becomes jerkier. At 15fps video will still look acceptably smooth. Below this, the jerkiness becomes noticeable.

Generally,  decrease the video frame rate in order to achieve higher compression. You can also increase the frame rate, but that is not recommended, since the output file will be bigger and the quality will not be any better. For example, if the original video is 15fps and you compress it as 30fps, the compressed video will NOT be smoother than the original.

The Input Frame Rate box displays the frame rate of the input video. This is for informational purposes only.

Use the Output Frame Rate drop-down list box to select one of the predefined output frame rates. When the output frame rate to Input frame rate, then the H.263 Encoder will not change the video frame rate. Select one of the other options  (3.000, 4.000, etc ) to use the specified frame rate for the output file. For example, selecting 15.000 will make the output video 15fps.

It is recommended to reduce the frame rate if you increase the quality factor to the point you start seeing compression artifacts and the compression is still not good enough. In that case, reduce the frame rate and reduce the quality factor and you might get better visual results.

Note: The Video For Windows (VFW) version of the codec cannot change the frame rate for the file. If you look at the properties for a file generated with the LEAD H.263 Codec (VFW), the frame rate will appear to be the same as the input file. But, if you play the file, you will notice that the frame rate is changed. Also, the VFW codec can only REDUCE the frame rate. If you convert a file that is 15fps and try to convert the file to 30fps, the generated file will still be 15fps.

Other Options group

Select the RTP check box to packet an H.263 video stream with Real-Time Transport Protocol (RTP) headers. This should be done when transmitting H.263 video streams over the Internet. If the codec is not being used inside a videoconferencing application, we do not recommend using this option.

Select the Enable High Compression check box to enable the high compression mode, which is a non-standard extension introduced by LEAD Technologies, Inc. to the H.263 compression algorithm. The result of such compression is a smaller video, but only the LEAD H.263 Decoder can decode this video.

Select the Output Sorenson Video (Flash) check box to enable Sorenson video, which is a non-standard extension introduced by Sorenson Media, Inc. to the H.263 compression algorithm. This format is used in Flash (FLV) files. Leave this check box unselected to generate regular H.263 video (including video for 3GPP format).

GOP settings (Group Of Pictures settings)

Use the controls in the GOP Settings group to specify the distance between key frames and the number of B frames encoded between two P frames. Key frames are frames compressed independently and they have the best quality in the video. In highly compressed video, you will notice that at regular intervals, the video starts looking good, then it degrades, then it fixes itself, it degrades again, etc. The encoding of a key frame causes the fix. So the more key frames you have, the better the video will look. There is a price for that: key frames are a lot larger then the non-key frames, so the more key frames you have the lower the compression will be.

Also, the more key frames are used the faster the seek operations. Seeks occur when you play a video file and you try to skip ahead in the movie. You will notice that the playback does not start immediately. Reduce the delay between the seek and when the playback starts by reducing the distance between key frames.

The distance between key frames to be can be specified either in Seconds or Frames. For example, to have a key frame to come every 3 seconds, set the unit to Seconds and the distance to 3. To have the key frame to come every 90 frames, set the unit to Frames and the distance to 90. Note that, for a 30fps video, 90 frames is equivalent to 3 seconds. For a 10fps video, 90 frames is equivalent to 9 seconds.

Use the Key Frame Interval Unit radio buttons to specify whether the distance between key frames is in Seconds or Frames. Use the Key frame interval to specify the maximum distance between key frames. Note that the codec might still insert additional key frames if it detects that a new key frame is necessary. A new key frame is generated sooner if the background changes too much and the current key frame is not suitable anymore for the frames being compressed.

I Frames and P Frames

A video stream is comprised of I Frames, B Frames and P Frames:

• I: (Intraframe, or key frame) frames are the largest frames, with the best quality and can be used for seeking and resynchronization. They are compressed independently and do not depend on other frames.

• P: (Predictive) frames are encoded using the previous I (or P) frame as reference. P frames are compressed more than I frames. P frames are smaller than I frames, with less quality but higher compression. They depend on the previous I or P frame.

• 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. B frames are smaller than I frames, with less quality but higher compression. They depend on the previous I or P and on the next I or P frames. They are usually smaller than P frames, but that is not guaranteed. They also take longer to compress than P frames.

Use more B and P frames (using the selections in the No. of Bs between 2 Ps drop-down list) to increase compression.  The 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.

General notes

1) When the encoder is in Constant Bitrate mode (CBR), the generated bitrate will be close to, but not exactly the rate requested. If the rate is too low for the video dimensions (width x height) and the frame rate, the achieved bitrate might not be even close to what you requested. Also, if you generate AVI files, keep in mind that, by default, the generated AVI files will have padding with JUNK chunks. The padding is intended to speed up the playback by aligning the compressed chunks in the file to multiples of 512. This can distort the real achieved video bitrate and will make it seem like the compressor did not compress too much. To avoid this, you need to set the multiplexing mode in the AVI muxer properties to Full. Here is a screen shot of this setting as obtained with the M2Convert Pro application (see http://www.m2solutionsinc.com/):

If you save AVI files using a different application, please consult the applications documentation to find out how you turn on the full multiplexing when creating AVI files. Or you can avoid all these problems by using Ogg files, which have a much lower overhead than AVI files.

Also, if you save video and audio, it will be harder to tell what the video bitrate is. The custom bitrate from the video compressor is the target bitrate for the video stream. The generated files bitrate will be higher, because it will contain video, audio and the overhead of the file format.

The generated bitrate (in bits/second) for a particular file is

Bitrate_bps = file_size_bytes * 8 / file_duration_seconds.

Generating a 3GPP H.263 Stream

It is possible to create a 3GPP H.263 stream that will play on mobile phones by using the LEAD H263 Encoder, the LEAD AMR Audio Encoder, and the LEAD ISO Mixer, along with the Resize Filter and Frame Rate Controller.

The following H.263 settings are suggested:

ILMH263Codec:: put_UseQuality(VARIANT_FALSE);

ILMH263Codec::put_UsePredefinedBitrate(VARIANT_FALSE);

ILMH263Codec::put_CustomBitrate(64000);

ILMH263Codec::put_UsePredefinedSpeed(VARIANT_FALSE);

ILMH263Codec::put_UseUnrestrictedMotionVector(VARIANT_FALSE);

ILMH263Codec::put_UsePBFrame(VARIANT_FALSE);

ILMH263Codec::put_UseDeblockingFilter(VARIANT_FALSE);

ILMH263Codec::put_UseAdvancedIntraCoding(VARIANT_FALSE);

ILMH263Codec::put_UseAdvancedPredictionMode(VARIANT_FALSE);

ILMH263Codec::put_OutputFrameRate(-1.0);

ILMH263Codec::put_UseRTP(VARIANT_FALSE);

ILMH263Codec::put_UseSuperCompression(VARIANT_FALSE);

ILMH263Codec::put_IDistanceUnit(UNIT_SECONDS);

ILMH263Codec::put_IDistance(60);

ILMH263Codec::put_PDistance(0);

ILMH263Codec::put_SorensonOutput(VARIANT_FALSE);

Please note the following about these settings:

•  The average video bitrate must not exceed 64000

•  Various I frame distances can be used, but keeping the P frame distance at 0 is recommended

•  The frame rate cannot exceed 14.985 fps.

•  The video dimensions have to be 128x96 or 176x144