Opened 6 months ago

#9363 new enhancement

loudnorm does not allow a loudness range beyond 20 LU

Reported by: Llyw Owned by:
Priority: normal Component: avfilter
Version: Keywords: loudnorm loudness range lra
Cc: Llyw Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no

Description

The loudnorm filter provided with FFmpeg 4.4 does not allow a loudness range (LRA) parameter beyond 20.

I would like to request for that limit to be extended and, if possible, allow the value inf such that no compression is enforced based on the loudness range of the input file.

I am not sure why the current limit of at most 20 LU of LRA is currently being imposed, but my reasoning for my request is that certain movies easily exceed an LRA of 20 LU such as The Matrix as shown in https://tech.ebu.ch/docs/tech/tech3343.pdf, section 11.2.2. According to the AES presentation https://www.aes.org/technical/documentDownloads.cfm?docID=521, section "Loudness vs. Speech: Transparency", feature films can more generally easily reach a LRA ranging from 16-30 LU.

Additionally, both the EBU R 128 guideline (near the end of section 11.2.2) and https://auphonic.com/blog/2019/08/19/dynamic-range-processing/ in section "Where LRA falls short" explain that the LRA value should at least in general not be used for specifying a dynamic range target value. (The EBU R 128 guideline goes on to suggest that the Maximum Short-term Loudness Level should be used instead but this clearly goes beyond this request for enhancement.)

So the first observation gives justification of an increase of the upper limit of loudnorm's LRA parameter, the second observation gives justification for also making the LRA constraint optional when using loudnorm.

I am looking forward to getting feedback from you concerning this request.

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