blob.rst

Blob As Files

Unlike other data formats, large multimodal data is a first-class citizen in the Lance columnar format. Lance provides a high-level API to store and retrieve large binary objects (blobs) in Lance datasets.

Lance serves large binary data using :py:class:`lance.BlobFile`, which is a file-like object that lazily reads large binary objects.

.. autoclass:: lance.BlobFile
    :members:
    :show-inheritance:
    :noindex:

To fetch blobs from a Lance dataset, you can use :py:meth:`lance.dataset.LanceDataset.take_blobs`.

For example, it's easy to use BlobFile to extract frames from a video file without loading the entire video into memory.

# pip install av pylance

import av
import lance

ds = lance.dataset("./youtube.lance")
start_time, end_time = 500, 1000
blobs = ds.take_blobs([5], "video")
with av.open(blobs[0]) as container:
    stream = container.streams.video[0]
    stream.codec_context.skip_frame = "NONKEY"

    start_time = start_time / stream.time_base
    start_time = start_time.as_integer_ratio()[0]
    end_time = end_time / stream.time_base
    container.seek(start_time, stream=stream)

    for frame in container.decode(stream):
        if frame.time > end_time:
            break
        display(frame.to_image())
        clear_output(wait=True)