st40_rfc8331_rtp_hdr does not support little endian

[steve-icc]

MTL maint-25.02.1

For the structure st40_rfc8331_rtp_hdr in st40_api.h, it is currently implemented for big-endian. The sub-structure (i.e. anc_count, f, reserved) seems to be incorrect in little-endian machines.

Please advise if this is an oversight.
Thanks

[MateuszGrabuszynski]

Hello @steve-icc,

Thank you for your message! I took a look and I agree - that seems like an oversight.

I am directly working on different Open Visual Cloud projects, not Media Transport Library, but I pushed a small PR to patch that. It needs to be tested, before merging.

Kind regards,
Mateusz

[steve-icc]

Thanks Mateusz. But I think we need to do more than that. If we follow your fix, we will need to add a union with a uint32_t "swap" and call ntohl() on it. See st40_rfc8331_payload_hdr for reference.

Another approach is by defining the sub-structure for little-endian as below:

#ifdef MTL_LITTLE_ENDIAN
struct {
uint32_t anc_count : 8;
uint32_t reserved : 6;
uint32_t f : 2;
uint32_t reserved2 : 16;
};
#else

The reserved field breaks up into 2 fields. But I am hesitant to do it because it becomes inconsistent with the big-endian structure (i.e. there is no reserved2 for big-endian).

Steve

[MateuszGrabuszynski]

Right, I have not thought about it. Thank you for pointing that. I will try to find more time to analyze, test and provide a solution.