Re: [FFmpeg-devel] [PATCH 2/2] avutil: add HDR10+ dynamic metadata serialization function

["Raphaël Zumer" <raphael.zumer@vimeo.com>]

On 3/2/23 13:33, quietvoid wrote:
> This patch series mentions that it would be used for AV1, however the AV1
> specification is clear that the payload does not contain the country code.
> https://aomediacodec.github.io/av1-hdr10plus/#hdr10plus-metadata, Figure 1.
>
> So far all the AV1 HDR10+ conformance samples also respect this.
> There would probably be a need to specify which behaviour is wanted.
> The SEI for HEVC does keep the country code in the payload, but not AV1.

As you pointed out, HEVC does include the country code in the payload, so either approach can be seen as reasonable. There are a few reasons why I don't think it makes sense to reproduce the AV1 specification:

- it does not make sense to exclude the country code from the payload while including other static headers like the terminal provider codes and the application identifier, so there is no particular advantage or logic that I can see in splitting the payload in that way.

- pragmatically, it is much less inconvenient to deal with a 1-byte offset in the payload for AV1 than it is to insert that byte into the payload for HEVC and other applications that expect the country code to be included in the header. For the same reason, I think that an option to include or exclude the country code byte would be more trouble than it's worth.

- perhaps most importantly, the payload syntax is standardized in ANSI/CTA-861-H, which does not make any distinction between the header (country code, terminal provider code, etc.) and the remainder of the payload, so the AV1 specification does not conform either to other implementations nor to the standard. Following the most authoritative document is the safest route in my opinion.

Raphaël Zumer

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