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Bongo comes with a separate integrated video encoder application that can combine a sequence of rendered images into a single video file.
The file extension must be either AVI, MPG, WMV or OGV. The encoder will determine which type of compression options to display depending on this type.
Render an animation with the "Create video file" option enabled, the Video Encoder dialog box appears when all of the animation images have been rendered and automatically compiles the video file.
To produce an AVI or MPG file from a sequence of stills, Bongo uses a codec (compressor/de-compressor). There are many different codecs available and your computer will have many installed already. Codecs compress images into a single file removing information until they are small enough to be played at the correct speed. The quality of the output depends a great deal on the quality and type of the codec and the data rate (the speed the information is read from the file) and can vary from extremely poor to virtually perfect.
If you are writing to an MPG file, you will not have to worry about choosing a codec. MPG uses MPEG-1 compression that is very compatible and produces reasonable quality at a small size. You may still want to set the data rate. If you are writing to AVI, you will need to consider carefully how to compress the video.
Choosing a codec is tricky. In addition to quality factors, you may need to take into account the size of the resulting file (determined mainly by the data rate) and the likelihood of it working on another computer. These are the three factors to consider when choosing a codec: quality, file size, compatibility.
In general, higher quality is possible only with increased size. The size of the output file can be estimated by this formula:
Size (kilobytes) = Data Rate x Run Time (in seconds)
Individual codecs will recommend a certain data rate to achieve a reasonable level of quality.
Note: Bongo does not come with codecs but uses what you have on your computer. Many codecs can be downloaded from the internet.
A full discussion of codecs is beyond the scope of this document. More information on codecs can be found any various books and Internet sites. For example:
A document about choosing a video file format can be found here.
As one of the older codecs, Cinepak is extremely compatible. It can be played on almost any target machine. However, while it tends to produce reasonably small files, it never achieves a good quality. Artifacts are usually visible trailing moving objects.
Almost as old as Cinepak, MSV1 generally produces poor results at a reasonable file size. Playable on any Windows machine, it tends to produce square looking artifacts.
These codecs are of a high quality – particularly the 5.0 version. They produce fairly large files, but the quality is high. Not installed on all machines though, and some licensing issues mean that this codec may not be available in the future.
Despite being an MPEG compressor, this codec is used with AVI files. Very high quality, this codec was designed specifically for Internet use and so produces reasonably small files. However, MPEG-4 is very modern and will not be playable on all computers as the codec may not be installed or the processor may not be powerful enough to cope with the high compression.
A very popular codec, this compressor uses a very similar technology to MPEG-4. However, a special but freely available download is required to allow it to play on target computers (as well as to enable compression in Bongo). www.divx.com
An open source free alternative to DivX
If you have made a bad choice of codec or you want to compress your video for several different uses, you may want to use the video encoder in interactive mode (BongoVideoEncoder command) to re-write the AVI or MPG file. Because Bongo saves the entire output of the renderer in the single-frame sequence you can re-compress from the original data ensuring you get the best possible quality.
The Bongo video encoder cannot re-compress AVI or MPG files. You will need to use a third-party application to do this. Remember that re-compressing a video file such as an AVI results in lower quality for every generation.
Usually the video encoder will be launched automatically after completing rendering. However, in certain cases you may want to use the encoder on its own.
The Bongo Video Encoder takes a numbered sequence of images and writes either an AVI, MPG, WMV, or OGV file, sets the frame rate, the start and end frames, and the compression options.
Enter the path to one of the images to be compressed or click Browse to select an existing file.
Enter the full path to the output file. The file extension must be either AVI, MPG, WMV, or OGV.
Launches the preview and codec window. The codec, data rate, and other options can be set here. If compression options are not set, the encoder uses the last codec specified for the target file type.
Enter the first and last frames from the image sequence to compress.
The number of frames per second displayed by the video file.
See also: Render the Animation.
The Compress button changes to Play when the compression is finished. The Play button will launch the video file in the associated media player.
Next article: Object properties and constraints