Usage Notes

This page collects practical details that are easier to keep out of the quickstart: when each compression method is useful, how shorthand levels work, what optional dependencies do, and how the non-training buffers fit in.

Input types

Compression is most effective when the stored observations have repeated values or structure. The README calls out these common cases:

semantic segmentation masks,
color-palette frames from retro games,
grayscale observations,
RGB observations when the image is not too noisy.

For noisy RGB observations, prefer zstd first. Run-length encoding can still decompress quickly, but it may save much less memory and can even increase storage for highly varied inputs.

Compression algorithms

See Supported Compression Algorithms

Buffer dtype settings

Most examples pass the result of sb3_extra_buffers.compressed.find_buffer_dtypes() into the buffer kwargs:

buffer_dtypes = find_buffer_dtypes(
    obs_shape=env.observation_space.shape,
    elem_dtype=env.observation_space.dtype,
    compression_method=compression,
)

rollout_buffer_kwargs = {
    "dtypes": buffer_dtypes,
    "compression_method": compression,
}

The helper returns an elem_type and runs_type mapping. elem_type controls the stored observation element dtype. runs_type controls the integer dtype used for run lengths in RLE-style compression.

Recording buffers

Recording buffers are useful when you want to keep a fixed-size circular record of frames, rewards, actions, and optional features for debugging or offline inspection.

from sb3_extra_buffers.recording import RecordBuffer

record_buffer = RecordBuffer(res=(84, 84), ch_num=4, size=40_000)
record_buffer.add(frame, reward, action)

Use FramelessRecordBuffer when you only need rewards/actions/features, or DummyRecordBuffer when recording should be disabled without changing the calling code.

Training utilities

The sb3_extra_buffers.training_utils package contains helpers used by the examples and benchmarks:

sb3_extra_buffers.training_utils.atari.make_env() builds Atari vector environments, applies optional frame stacking, and returns channel-first observations through VecTransposeImage.
sb3_extra_buffers.training_utils.eval_model.eval_model() evaluates a model and can fill one or more replay-like buffers with transitions.
sb3_extra_buffers.training_utils.buffer_warmup.warm_up() uses a trained model and environment to pre-fill replay buffers before another training run.

Testing

The test suite can be run with plain pytest:

pytest tests -v --durations=0 --tb=short

The tests are compatible with pytest-xdist because DummyVecEnv is used for test environments:

pytest tests -n auto -v --durations=0 --tb=short

By default, tests may save observations under debug_obs/ for manual inspection. Disable that behavior in CI or low-disk environments with:

DISABLE_TEST_OBSERVATIONS_SAVE=true pytest tests -v

Experimental helpers

The sb3_extra_buffers.vec_buf and sb3_extra_buffers.gpu_buffers packages expose experimental helpers. Treat their APIs as less stable than the compressed and recording buffer APIs.