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Netflix / photon

Photon is a Java implementation of the Interoperable Master Format (IMF) standard. IMF is a SMPTE standard whose core constraints are defined in the specification st2067-2:2013
Apache License 2.0
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Incorrect Sample Rate validation for non App2E interlaced content #369

Open harrietmiller opened 5 months ago

harrietmiller commented 5 months ago

Problem When using com.netflix.imflibrary.app.IMPAnalyzer we get an incorrect (and confusing) error report for interlaced content that is not App2E:

EssenceDescriptorList represented by the ID urn:uuid:1172379b-1e95-4917-a460-c73ab91a4d5a whose indicated SampleRate value is =================== EditRate =====================
    numerator = 12, denominator = 1
    , however the Resource Edit Rate is =================== EditRate =====================
    numerator = 25, denominator = 1

For this example, in the App6 Image Track File the SampleRate and the EditRate are both 25/1 which is correct (the frame rate). The reported SampleRate value (above) is actually the SampleRate of the EssenceDescriptor divided by 2 (and then rounded down).

This issue potentially applies to all interlaced content that is not App2E. A similar issue has been reported here for interlaced ProRes content.

Proposal of solution When Photon handles interlaced content the relationship between SampleRate and EditRate is dependent on the Application ID and not just the FrameLayout (therefore should not be checked as part of core constraints).

Problem details In the IMFCoreConstraintsChecker (link) class, the SampleRateToEditRateScale is derived from looking at the FrameLayout. If FrameLayout is SeparateFields then the SampleRateToEditRateScale is set to 2 otherwise it is 1.

According to both Application 6 (SMPTE ST 2067-60:2023) & Application 2E (SMPTE ST 2067-21:2023) the FrameLayout of interlaced content must equal “SEPARATE_FIELDS”. However:

Other Applications could have other rules.

Note: This issue is more confusing as App6 (for example) is not in line with SMPTE ST 377-1 (because App6 is based on SMPTE ST 381-3).

palemieux commented 1 month ago

This issue is specifically about factoring out the application-specific check to the application-specific class. It is not about Application 6 support.