Two different questions hide behind "what does JAVE support": which container you can read and write, which is EncodingAttributes.setOutputFormat("mp4"), and which codec goes inside it, which is setCodec("libx264") on the audio or video attributes. They are chosen separately and not every pairing is legal.

The lists below were generated from the bundled ffmpeg 9.0.1 on windows x64. They are a snapshot, they go stale, and they are not identical on every platform. The authoritative answer always comes from the executable you are actually running:

Encoder encoder = new Encoder();

encoder.getSupportedEncodingFormats();  // containers you can write
encoder.getSupportedDecodingFormats();  // containers you can read
encoder.getAudioEncoders();
encoder.getVideoEncoders();
encoder.getAudioDecoders();
encoder.getVideoDecoders();

Each returns a String[] and throws EncoderException. These are the names to pass to setOutputFormat and setCodec, so a program that has to cope with an unknown deployment can check first rather than catching a failure afterwards.

The core codecs are on every platform, and the build is checked against that list in CI, so these can be relied on everywhere:

libx264, libmp3lame, aac, libvorbis, flac, mpeg4, libopus, libvpx-vp9

Beyond those:

• libx265 is on every platform except linux arm 32 bit, where it is left out because it does not build reliably there.
• Hardware encoders differ completely. The windows binary carries NVENC, AMF, QSV and the Direct3D paths; macOS has VideoToolbox; our linux binaries are static musl builds with no hardware acceleration at all, deliberately, since that is what lets them run anywhere without a libc. Do not assume h264_nvenc exists.
• A handful of rarely used software encoders vary with the build.

This is exactly why the query methods above are worth using when a codec matters.

Out of the 126 video and 86 audio encoders in this build, this is what covers almost every real request. See Examples for these in context.

One name is not a codec at all: copy, which the library also spells AudioAttributes.DIRECT_STREAM_COPY and VideoAttributes.DIRECT_STREAM_COPY. It takes the stream across untouched, which is fast and lossless, but only works when the target container accepts the codec that is already there. It is also what keeps album art through an audio conversion.

libaom-av1 is thorough rather than quick. For anything long, expect it to be very much slower than x264 or x265 at default settings.

From ffmpeg 9.0.1, windows x64.

Decoding rarely needs a name: ffmpeg picks the decoder from what it finds in the file, so the decoder lists are here for checking whether something can be read at all.

It came from the bundled binary, so it can be produced again rather than edited by hand:

ffmpeg -hide_banner -formats  > formats.txt
ffmpeg -hide_banner -encoders > encoders.txt
ffmpeg -hide_banner -decoders > decoders.txt

• Examples -- these codecs in working conversions
• Encoding Attributes -- the settings that go with them
• Custom ffmpeg arguments -- codec options this API does not model