GIFCompressor
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Strategies

How to choose compression options [edit this page]

Track strategies return options for the engine to understand how the GIF file (or files) should be compressed.

Transcoder.into(filePath)
        .setStrategy(strategy)
        // ...

The point of Strategy is to inspect the input android.media.MediaFormat and return the output android.media.MediaFormat, filled with required options.

This library offers a default strategy that covers most use cases, called DefaultStrategy. This strategy converts the GIF stream to AVC format and is very configurable.

Frame Size

The DefaultStrategy helps in defining a consistent output size. If the chosen size does not match the aspect ratio of the input GIF(s) size, GIFCompressor will automatically crop part of the input so it matches the final ratio.

We provide helpers for common tasks:

DefaultStrategy strategy;

// Sets an exact size. If aspect ratio does not match, cropping will take place.
strategy = DefaultStrategy.exact(1080, 720).build();

// Keeps the aspect ratio, but scales down the input size with the given fraction.
strategy = DefaultStrategy.fraction(0.5F).build();

// Ensures that each video size is at most the given value - scales down otherwise.
strategy = DefaultStrategy.atMost(1000).build();

// Ensures that minor and major dimension are at most the given values - scales down otherwise.
strategy = DefaultStrategy.atMost(500, 1000).build();

In fact, all of these will simply call new DefaultStrategy.Builder(resizer) with a special resizer. We offer handy resizers:

Name Description
ExactResizer Returns the exact dimensions passed to the constructor.
AspectRatioResizer Crops the input size to match the given aspect ratio.
FractionResizer Reduces the input size by the given fraction (0..1).
AtMostResizer If needed, reduces the input size so that the “at most” constraints are matched. Aspect ratio is kept.
PassThroughResizer Returns the input size unchanged.

You can also group resizers through MultiResizer, which applies resizers in chain:

// First scales down, then ensures size is at most 1000. Order matters!
Resizer resizer = new MultiResizer();
resizer.addResizer(new FractionResizer(0.5F));
resizer.addResizer(new AtMostResizer(1000));

// First makes it 16:9, then ensures size is at most 1000. Order matters!
Resizer resizer = new MultiResizer();
resizer.addResizer(new AspectRatioResizer(16F / 9F));
resizer.addResizer(new AtMostResizer(1000));

This option is already available through the DefaultStrategy builder, so you can do:

DefaultStrategy strategy = new DefaultStrategy.Builder()
        .addResizer(new AspectRatioResizer(16F / 9F))
        .addResizer(new FractionResizer(0.5F))
        .addResizer(new AtMostResizer(1000))
        .build();

Other options

You can configure the DefaultStrategy with other options unrelated to the video size:

DefaultStrategy strategy = new DefaultStrategy.Builder()
        .bitRate(bitRate)
        .bitRate(DefaultVideoStrategy.BITRATE_UNKNOWN) // tries to estimate
        .frameRate(frameRate) // will be capped to the input frameRate
        .keyFrameInterval(interval) // interval between key-frames in seconds
        .build();

Compatibility

As stated pretty much everywhere, not all codecs/devices/manufacturers support all sizes/options. This is a complex issue which has no easy solution - a wrong size can lead to a compression error or corrupted file.

Android platform specifies requirements for manufacturers through the CTS (Compatibility test suite). Only a few codecs and sizes are strictly required to work.

We collect common presets in the DefaultStrategies class:

GIFCompressor.into(filePath)
        .setStrategy(DefaultStrategies.for720x1280()) // 16:9
        .setStrategy(DefaultStrategies.for360x480()) // 4:3
        // ...