I closed the pull request to make some fixes, and now it is open again.

Below is a zip file containing:
Test.msg, a message type with a timestamp and a string message.
test_control_in.py, a python script that simply prints a timestamped message 20 times a second, used to create a bag.
2016-12-15-12-17-30.bag, a bag file created by recording the output of the above script for 60 seconds.
test_control.py, a python script that simulates a processing function by waiting 100 ms every time it waits a message, before it can receive another.

To test, run test_control.py, then run

rosrun rosbag play --rate-control-topic /test/out --rate-control-max-delay 1.0 --bags /home/eric/ros_workspace/2016-12-15-12-17-30.bag

If the test_control.py script becomes more than 1 second behind, the rosbag playback will be automatically delayed until the test_control.py script catches up.

This is a useful feature to allow rosbag playback that prioritizes processing every message, rather than running at the required rate.

RateControlTopicTest.zip

Added arguments

--rate-control-topic /some/topic

• Watch the given topic, and if the last publish was more than [rate-control-max-delay] ago, wait until the topic publishes again to continue playback
• Defaults to empty string

--rate-control-max-delay 12.34

• Maximum time difference in seconds from the timestamp in [rate-control-topic] to bag time before pausing
• Defaults to 1.0

Use Case

Playing back recorded lidar data to build a map offline, but how fast can the bag run without dropping messages?

Example

The bag was recorded at 20Hz. A simulated system can only handle 10Hz. This shows the benefits of the added rate-control arguments.

• Start a roscore
  • roscore
• Simulate 100ms processing delay with queue size of 10
  • ./test.py
• Play bag with messages every 50ms, some messages will be dropped
  • rosrun rosbag play test.bag --clock -r 1.0
• Play bag with rate control, bag will pause to prevent dropped messages
  • rosrun rosbag play test.bag --clock -r 1.0 --rate-control-topic /test/out --rate-control-max-delay 0.5

test.tar.gz

@mastereric Thanks for addressing the compilation problem. In the mean time I have resolved the merge conflict to make the patch mergable again. @kmhallen Can you please try this again and update your review status.

This change does break ABI. @ros/ros_comm-maintainers what do you think? Should this target Lunar instead?

We already broke rosbag::Player ABI recently, see discussion in #949 (comment), so I don't think it's a concern.

Is it designed to work with only one topic in the bag file? What happens in the following scenario:

• Bag file has multiple topics
• Node subscribe to one topic and publish one topic (rate-control-topic)

Yes, it was designed to work with one topic. The bag playback will pause, so all topics will stop until the rate-control-topic catches up.