DivX Tutorial

Fx, Sound & Magic

DivX Compression Tutorial - Using VirtualDub

The current version of the DivX codec works well and produces small, high quality videos.

The early versions such as DivX ;-) and Angel Potion are garbage that will crash your computer.

DivX 4.11 and 4.12 will not work on a Pentium, Pentium MMX, or AMD K6/K6-2/K6-3 due to use of a Pentium Pro instruction and will cause a crash.

There's a bug in the DivX 5.0.2 Pro Bundle codec that prevents the Direct Show FrameGrabber from working. Upgrade to the latest using the link below.

Although you can use any software that you like to compress movies in this example we're using VirtualDub.

Before proceeding please download and install both DivX and VirtualDub

NOTE: When you install DivX be sure to elect to have it play earlier versions.

Step-by-Step

1. Open your uncompressed video file.

2. From the Video menu, select Compression ...

3. Select the DivX 4.x Codec.

If you see any older versions of DivX ;-) or Angel Potion you should remove them from your system.

If you have a DirectX multimedia application such as Fx Joiner or Fx Splitter you may notice that the list of codecs is somewhat different than those displayed by VirtualDub. That's because VirtualDub uses Video For Windows technology rather than DirectX.

4. Configure the codec.

Codec General Parameters

1-pass - The encoder will try to match the average bit rate of movie to the specified value by omitting information in fast-motion scenes.

1-pass quality-based mode - All frames are compressed equally without regard to their complexity. You might use this method when saving a file for future use or when your goal is to preserve the quality of all frames.

2-pass variable bit rate mode - The encoder will attempt to make the subjective quality of the stream constant while creating a stream size to match the size you specified. You might chose this option if you wanted to encode a 2-hour session to fit on a 650 Mb CD. This mode is the most complicated since it requires the source to be processed twice.

It may be important to note that 2-pass encoding writes a temporary file to your hard disk as well as a Log File. If you don't have sufficient room on your drive for both a temp file and a log file or if you haven't specified a valid path to a writable log file the codec may cause the program to crash.

During the first of the 2 Passes, the encoder will analyze the source and create the log file with information about the frames. When the first pass is finished, return to the configuration dialog and select "variable bit rate mode" --> "2-pass, second pass."

During the second pass the encoder will read the log file that was created in the first pass and it will write the final Variable Bit Rate AVI to the location you've specified.

It is recommended that you use the same "performance/quality" setting for both passes, but not an absolute requirement. The performance/quality mode of "fastest" should not be used for either pass. If you use different values for "bit rate" in first and second passes they cannot differ by more than 50% or the encoder may not achieve the file size that you want.

Performance/quality - Performance and quality are inversely proportional. On state-of-the art computers performance variables will not even be noticeable but a high quality movie may not play on a less powerful computer.

Slowest = highest quality, plays well on faster, more powerful machines.
Slow = sacrifices some quality for speed.
Medium = sacrifices more quality for speed.
Fast = sacrifices a good deal of quality for speed.
Fastest = poorest quality, necessary for slower, less powerful machines.

Output Video Bit stream - Applicable during 1 pass encoding, this parameter allows you to set the bit stream in kilobits per second.

Maximum key frame interval - A key frame is a reference point like an index that allows software to "seek" a particular frame. The encoder will insert a key frame at every scene change and at default rate of 300 which is one key frame for every 10 seconds in a 30 fps stream.

Max CPU - Sets the percentage of processor time that the encoder will use.

De-interlacing - Video streams captured from TV or VCR in high resolutions usually contain "interlacing" artifacts. For example the maximum height for NTSC is 480 lines at 30 frames per second but the actual television signal has only 240 visible lines at 60 cycles. As a result the captured streams will contain interleaving lines from two subsequent "fields," which have different positions in time.

Decoding Parameters

Post-processing - The post-processing algorithms consist of de-blocking on luminance planes, de-blocking on chrominance planes and de-ringing. Results vary dramatically based upon computer resources and may actually take longer than decoding. Some experimentation may be in order.

1 Pass Encoding Parameters

MAX and MIN Quantizers - The Quantizer is arguably the most important parameter of the encoder. The smaller the Quantizer value the better the quality and the higher the bit consumption.

Rate Control Averaging Period, frames - The Rate Control Averaging period is the time in history that the codec remembers.Larger values generally result in more accurate overall rates.

Rate Control Reaction Period, frames - The Rate Control Reaction period determines how many frames will pass before the codec reacts to a change such as when very fast motion shifts to slower motion. In a typical movie, 30 frames is equal to one second.

Rate Control Down/Up Reaction Ratio - The reaction down/up ratio essentially affects how long a high motion burst can be obtained before it is suppressed by Rate Control. A larger value should result in better high motion scenes.

Quality Based Encoding Parameters

Encoding Quality - This value can be changed when encoding in 1-pass quality and will automatically set your 1 pass parameters based on the percentage selected.

2 Pass Encoding Parameters

Log file - The location where the log file is written.

Frame dropping - This parameter, available only in 2-pass variable bit rate mode, allows the encoder to selectively drop frames that do not contain significant information. The percentage determines the drop/don't drop threshold.

5. Be sure that Full processing mode is elected from the Video menu ...

6. Determine the audio frequency of your source file. Locate the file in Windows Explorer then right-click on the file and select Properties and look at the Summary tab.

7. From the Audio menu, select compression and set it to MPEG-3 with frequency matching that of your original AVI file with a bit-rate of at least 96. You may need to turn on the "Show all format" option to see all the available options.

8. Select the AVI audio and Full processing mode options.

9. From the file menu select "Save AVI", enter a name that's different from the original AVI.