Warnings while starting realsense-viewer (patch for fourcc code RW16, relevant metadata params are missing, Invalid md size)

[HartmannSa]

Required Info
Camera Model	D435
Firmware Version	05.12.10.00
Operating System & Version	Ubuntu 18.04.5 LTS
Kernel Version (Linux Only)	5.4.0-65-generic
Platform	PC
SDK Version	librealsense2.41.0-0

Issue Description

I get the following warnings when starting the realsense-viewer:

 05/02 12:03:43,797 WARNING [140316942813056] (backend-v4l2.cpp:1357) Pixel format 36315752-1a66-a242-9065-d01814a likely requires patch for fourcc code RW16!
 05/02 12:03:54,454 WARNING [140316598310656] (hdr-merge.cpp:38) HDR Merge filter cannot process frames because relevant metadata params are missing
 05/02 12:03:58,119 WARNING [140316598310656] (backend-v4l2.cpp:1775) Invalid md size: bytes used =  0 ,start offset=10
 05/02 12:03:58,119 WARNING [140316598310656] (backend-v4l2.cpp:1775) Invalid md size: bytes used =  0 ,start offset=10
 05/02 12:03:58,119 WARNING [140316598310656] (backend-v4l2.cpp:1775) Invalid md size: bytes used =  0 ,start offset=10
 05/02 12:03:58,119 WARNING [140316598310656] (backend-v4l2.cpp:1775) Invalid md size: bytes used =  0 ,start offset=10

I found a similar issue #4971, however I do not use Kernel 4.16.
I have built the package from source.

What do these warnings mean?
What causes them?
And how can I fix them?
Before I completely uninstalled and reinstalled librealsense, these error messages never appeared.

[MartyG-RealSense]

Hi @HartmannSa I have seen a small cluster of cases involving an Invalid md size: bytes used = 0 ,start offset=10 with the RealSense Viewer program during the past month and they have only occured on SDK 2.41.0. An example of such a case that matches closely to your particular set of errors is in the link below.

#8154 (comment)

So I would suggest trying to build librealsense 2.40.0 from source code and if it works, see whether or not the problem still occurs in the upcoming SDK version that follows after 2.41.0.

[HartmannSa]

Okay thanks.
So, I would just do sudo make uninstall and then delete the folder.
And then download the correct version from here https://github.com/IntelRealSense/librealsense/releases and build it again.

Or is there an easy/ better way to downgrade?
(Something like git checkout aae6f31 for example and then build again?)

[MartyG-RealSense]

It would make logical sense to me to download the source code folder for 2.40.0 and go through the usual process of mkdir build && cd build to create the Build folder. And then run the full instruction for uninstall, clean-up and install as stated by the source-code installation documentation:

sudo make uninstall && make clean && make && sudo make install

https://github.com/IntelRealSense/librealsense/blob/master/doc/installation.md

[HartmannSa]

okay, thanks again for your fast reply!

The warning Invalid md size: bytes used = 0 ,start offset=10 doesnt show up with version 2.40.0.

The other warnings still occur (whereby the second warning only occurs when the depth stream is activated):

 05/02 20:01:39,339 WARNING [140204514723584] (backend-v4l2.cpp:1271) Pixel format 36315752-1a66-a242-9065-d01814a likely requires patch for fourcc code RW16!
 05/02 20:01:50,161 WARNING [140204354557696] (hdr-merge.cpp:38) HDR Merge filter cannot process frames because relevant metadata params are missing

Do you know something about them?

[MartyG-RealSense]

When the fourcc code RW16! message occurs, it would suggest a conflict with the Linux kernel. You could test this possibility by building librealsense from source code using the RSUSB installation method, which is not dependent on Linux versions or kernel versions and does not require patching.

[HartmannSa]

Can you explain what the implications of this warning are if I don't fix it?
I don't understand what the error message is trying to tell me.
Since everything else is currently working, I don't know if I should try a new build...

[MartyG-RealSense]

RealSense team member @ev-mp can provide a better technical explanation of fourcc code RW16! than I can. Below are links to a couple of previous comments by @ev-mp that make reference to the kernel patching topic though.

#4971 (comment)
#3686 (comment)

It is of course your choice whether you build again or not. It may come down to how much the error affects your use of librealsense overall.

[HartmannSa]

Thanks, I have read the comments. But they did not really help me.
If I understand correctly, the answers refer to the "problematic" kernel 4.16 (I have 5.4) and the realsense2-dkms package (which I don't use because of my installation from source).

[MartyG-RealSense]

The two links - which also feature fourcc code errors - were intended to be a general example of the problems that kernel conflicts can cause if they are not fixed. This was in reply to your question above of "Can you explain what the implications of this warning are if I don't fix it?"

@ev-mp would be better able than myself to provide information that relates specifically to the fourcc code error in your own case.

[MartyG-RealSense]

Hi @HartmannSa Do you require further assistance with this case, please? Thanks!

[HartmannSa]

Hi, since the warnings do not currently interfere with my program, I simply ignore them.
However, I was hoping that @ev-mp would answer my questions:

Can you explain what the implications of this warning are if I don't fix it?
I don't understand what the error message is trying to tell me.
Since everything else is currently working, I don't know if I should try a new build...

[MartyG-RealSense]

@HartmannSa Given that the RealSense user in the recent case that was the closest match to your set of errors in #8154 (comment) was given the advice that the next librealsense version after 2.41.0 should fix that case's errors, I would recommend waiting for the next SDK version to see if the changes in that version resolve your problem too.