AVIF rule #15: "stts" box can be omitted since all track samples are sync

Running libavif's ChangeSettingTest.AOM with -DAVIF_ENABLE_COMPLIANCE_WARDEN=ON gives:

Specification description: AVIF v1.0.0, 19 February 2019
https://aomediacodec.github.io/av1-avif/
[avif][Rule #15] Warning: "stts" box can be omitted since all track samples are sync

The check was introduced in 2c9031f.

I am trying to understand if the issue comes from libavif or from ComplianceWarden. I could not find anything related to an optional "stts" in ISO 23008-12 (HEIF), ISO 23000-22 (MIAF), ISO 23000-19 (CMAF), AV1-AVIF v1.0.0, AV1-AVIF v1.1.0 nor AV1-ISOBMFF v1.2.0. Section 8.6.1.2.1 of ISO 14496-12 (BMFF) says stts is mandatory.

Section 8.6.2.1 of ISO 14496-12 says stss is not mandatory, and "If the SyncSampleBox is not present, every sample is a sync sample." So I believe there is a typo and it should be stss instead of stts checked at

ComplianceWarden/src/specs/avif/avif.cpp

Lines 831 to 832 in bf096d4

    
           out->warning("\"stts\" box can be omitted since all " 
        
                        "track samples are sync");

@vigneshvg Vignesh: Could you take a look at this?

Yannis: I didn't consult the standards you cited, but I think your analysis is correct and that warning message should say "stss" instead of "stts".

You are right, let me fix this.

Should be good. Thanks for reporting!

Thanks for the fast fix!

	out->warning("\"stts\" box can be omitted since all "
	"track samples are sync");