Dolby Vision MEL and FEL
MEL and FEL distinguish Dolby Vision enhancement layers with no picture residual from layers that carry additional reconstruction information.
For dual-layer Dolby Vision UHD Blu-ray delivery, ask whether the enhancement adds a picture residual:
| Type | Expanded name | Picture residual |
|---|---|---|
| MEL | Minimum enhancement layer | Zero |
| FEL | Full enhancement layer | Nonzero |
Both remain part of a Dolby Vision presentation with associated metadata. The distinction concerns reconstruction information, rather than the amount of scene-specific guidance.
What the FEL adds to reconstruction
The authoring workflow prepares a base representation and an enhancement associated with it. With FEL, the enhancement supplies differences needed for the complete Dolby Vision reconstruction. The decoder/composer uses that information with the base and metadata.
Those differences can involve the prepared signal's precision and range. Their significance depends on the authored title. A larger enhancement stream can carry more coded correction data, but its byte size alone does not predict how obvious that correction will be in a scene.
With MEL, there is no nonzero picture residual to contribute. The presentation can still use Dolby Vision metadata and its specified base interpretation and mapping. “Minimum” therefore identifies the enhancement's residual role, rather than an absence of Dolby Vision processing.
Compare three paths from the same source
- Full FEL reconstruction: the relevant enhancement residual contributes to the composed picture before display adaptation.
- Base plus supported Dolby Vision processing: a route may use the base and applicable metadata while omitting that residual contribution.
- Compatible base presentation: Profile 7 can provide an HDR10 picture through its compatible base.
These paths can produce plausible images, but they use different source information. A final Dolby Vision output indicator cannot establish which reconstruction path occurred earlier.
For an Emby test, retain the exact source, profile/layer record, delivered stream, and decoder information. Use known content when examining whether enhancement data affects the picture. If a conversion discards an FEL, report that information loss even when the main base video was copied without re-encoding.