How to save image topics of Full-HD size with ROSBag

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Hello.

I'm trying to save image topic from Full-HD image camera. I ran my camera package on my pc. The publisher have 5 size of queue. I have used ImageTransport for publisher. the resolution of a image is 1920x1080. It is approximately 6 MB. And, It have 30 fps.

The throughput of result .bag file is not constant. The variation is 17~30. I tried to use some option for rosbag record like --buffsize, --chunksize. But there was no change for it. When I do that, the memory of RAM has continued to increase steadily.

I want to get images without throughput decrease. Is there any good solution or advise for me?

EDITED:

I saved images on the disk without communication using Ethernet.