Video

A stream of images (like those produced by a camera) can be logged to Rerun in several different ways:

• Uncompressed, as many Images
• Compressed as many EncodedImages, using e.g. JPEG.
• Compressed as a single AssetVideo, using e.g. MP4.

These alternatives range on a scale of "simple, lossless, and big" to "complex, lossy, and small".

If you want lossless encoded images (with no compression artifacts), then you should log each video frame as Image. This will use up a lot of space and bandwidth. You can also encode them as PNG and log them as EncodedImage, though it should be noted that PNG encoding usually does very little for the file size of photographic images.

If you want to reduce bandwidth and storage cost, you can encode each frame as a JPEG and log it using EncodedImage. This can easily reduce the file sizes by almost two orders of magnitude with minimal perceptual loss. This is also very simple to do, and the Python logging SDK has built-in support for it using Image.compress.

Finally, you can encode the images as a video file, and log it using AssetVideo. This gives the best compression ratio, reducing file sizes and bandwidth requirements.

"""Log a video asset using automatically determined frame references."""

import sys

import rerun as rr

if len(sys.argv) < 2:
    # TODO(#7354): Only mp4 is supported for now.
    print(f"Usage: {sys.argv[0]} <path_to_video.[mp4]>")
    sys.exit(1)

rr.init("rerun_example_asset_video_auto_frames", spawn=True)

# Log video asset which is referred to by frame references.
video_asset = rr.AssetVideo(path=sys.argv[1])
rr.log("video", video_asset, static=True)

# Send automatically determined video frame timestamps.
frame_timestamps_ns = video_asset.read_frame_timestamps_nanos()
rr.send_columns(
    "video",
    # Note timeline values don't have to be the same as the video timestamps.
    indexes=[rr.TimeColumn("video_time", duration=1e-9 * frame_timestamps_ns)],
    columns=rr.VideoFrameReference.columns_nanos(frame_timestamps_ns),
)

Video playback limitations video-playback-limitations

Video support is new in Rerun, and has a few limitations:

• #7354: Only the MP4 container format is supported
• #7755: No AV1 support on Linux ARM
• #5181: There is no audio support
• #7594: HDR video is not supported
• There is no video encoder in the Rerun SDK, so you need to create the video file yourself

Streaming video streaming-video

Rerun does not yet support streaming video support. For scenarios where you don't need live video, you can work around this limitation by logging many small AssetVideos to the same Entity Path. See #7484 for more.

Codec support codec-support

Overview overview

Codec support varies in the web & native viewer:

Details see below.

When choosing a codec, we recommend AV1, as it seems to have the best overall playback support while also having very high compression quality.

Since AV1 can have very long encoding times, it is often not suitable for streaming. In those cases where encoding time matters, we recommend H.264/avc.

Native viewer native-viewer

AV1

AV1 is supported out of the box using a software decoder paired with gpu based image conversion

H.264/avc

H.264/avc is supported via a separately installed FFmpeg binary, requiring a minimum version of 5.1.

The viewer does intentionally not come bundled with FFmpeg to avoid licensing issues. By default rerun will look for a system installed FFmpeg installation in PATH, but you can specify a custom path in the viewer's settings.

If you select a video that failed to play due to missing or incompatible FFmpeg binaries it will offer a download link to a build of FFmpeg for your platform.

Web viewer web-viewer

Video playback in the Rerun Web Viewer is done using the browser's own video decoder, so the exact supported codecs depend on your browser.

Overall, we recommend using Chrome or another Chromium-based browser, as it seems to have the best video support as of writing.

For decoding video in the Web Viewer, we use the WebCodecs API. This API enables us to take advantage of the browser's hardware accelerated video decoding capabilities. It is implemented by all modern browsers, but with varying levels of support for different codecs, and varying levels of quality.

When it comes to codecs, we aim to support any codec which the browser supports, but we currently cannot guarantee that all of them will work. For more information about which codecs are supported by which browser, see Video codecs on MDN.

We tested the following codecs in more detail:

Beyond this, for best compatibility we recommend:

• prefer YUV over RGB & monochrome formats
• don't use more than 8bit per color channel
• keep resolutions at 8k & lower (see also #3782)

Links links

• Web video codec guide, by Mozilla