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RTSP Image Transport for ROS

Overview

This package allow ROS nodes to publish and subscribe image topics using the Real Time Streaming Protocol (RTSP). Unlike regular image_transport plugins, the rtsp_image_transport does not transmit image data in-band. The publisher merely publishes a latched std_msgs/String message with the URL of an RFC 2326 compliant RTSP video stream server, from where the actual image data is served. The subscriber will listen for URLs on the ROS topic and automatically (re-)connect to the corresponding location.

Use Cases

rtsp_image_transport is intended for streaming live videos to one or more users. The RTSP server supports multicast transmission, so it will potentially save a huge amount of bandwidth if many clients are viewing the same video stream.

Limitations

If the image source is not a continuous video stream with roughly constant frame rate, you may experience problems such as session timeouts or degraded image quality.

rtsp_image_transport is not suitable for image data that is to be consumed by image processing algorithms. The lossy compression introduces artifacts which may not be visible to the human eye but interfere with many algorithms nevertheless.

You cannot use rosbag to record data from rtsp_image_transport; you will just end up with a bunch of useless URL string messages.

Supported Formats

rtsp_image_transport uses the Live555 library for its RTSP server and client implementation and the FFmpeg library for video compression. Starting with FFmpeg 4, some codecs are hardware acceleratable. The following table summarizes the options, subject to availability in your FFmpeg version and compatible hardware:

  Software NVIDIA VAAPI OMX
H.264 Yes Yes Encoding Encoding
H.265 Yes Yes Encoding No
MPEG-4 Yes Decoding Encoding No
VP8 Yes Decoding Encoding No
VP9 Yes Decoding Encoding No
MJPEG Decoding Decoding No No

Note

rtsp_image_transport cannot create Motion JPEG (MJPEG) streams, only receive them for backwards compatibility with some ancient IP cameras. If you really want to have independently compressed JPEG frames for your video stream, you can use the compressed_image_transport with JPEG compression instead.

IP cameras

The rtsp_image_transport plugin is compatible with many commercially available IP cameras. You can use the publish_rtsp_stream node to create an image topic with RTSP transport that reuses the existing RTSP stream.