Ok, I'm reading the Dolby "profiles and levels" spec:yusesope wrote: ↑Wed Mar 11, 2020 3:33 pmI believe that it is not possible to discard anything.
Regardless of the type of EL (fEL or mEL), in the case of a dvhe.04 or dvhe.07 profile, the Dolby Vision Composer accepts synchronized decoded BL and EL video frames and metadata information and uses metadata to reconstruct 12bit Dolby Vision video.
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2.1.1 Notes to profiles
For profile 4:
A new Dolby Vision certified device is able to decode a profile 4 MEL bitstream without instantiating a secondary HEVC decoder for the enhancement layer.
For profile 7:
The MEL can be used for profile 7 to minimize the processing requirements for the enhancement layer and therefore ensure broader use among UltraHD Blu-ray SoCs.
6.2 Annex II: Differentiating MEL and non-MEL bitstreams
Pictures contained in a Dolby Vision bitstream can be encoded as either MEL or non-MEL, not both.
If a Dolby Vision playback device supports Dolby Vision profile 4 and chooses not to instantiate a second HEVC decoder, then it must check for these values in the
reference processing unit of a Dolby Vision bitstream.
If a Dolby Vision playback device supports Dolby Vision profile 7, it can check for these values in the reference processing unit of a Dolby Vision bitstream.
Profile 4 - the doc explicitly states that the whole secondary decoder may be not instantiated at all (EL data discarded).
Profile 7 - the vague note that knowing about MEL can "minimize the processing requirements for the enhancement layer". I assume the same - no need to instantiate a second HEVC decoder, just generate same gray pictures as in profile 4.
And the fact that "dvdfab method" (BL+MEL RPU only, EL discarded) works, kind of proves that. Am I wrong?
Of course, EL is always 12 bit on blu-ray. The question is what exactly is in these 2 extra bits. My hypothesis - in MEL stream all pictures in EL are filled with the same value (zeroes). This is easy to verify though - one just has to decode entire EL from any MEL disc (Joker) and confirm that ALL frames in EL are indeed dark zero pictures. From the sizes of slice NALU it looks that way.