[FFmpeg-devel] [PATCH v3 1/2] lavu/dovi_meta - add fields for ext_mapping_idc

[Cosmin Stejerean]

> On May 23, 2024, at 4:03 AM, Niklas Haas <ffmpeg at haasn.xyz> wrote:
> 
> On Wed, 22 May 2024 15:50:43 +0000 Cosmin Stejerean via ffmpeg-devel <ffmpeg-devel at ffmpeg.org> wrote:
>> From: Cosmin Stejerean <cosmin at cosmin.at>
>> 
>> ---
>> libavutil/dovi_meta.h | 2 ++
>> libavutil/version.h   | 2 +-
>> 2 files changed, 3 insertions(+), 1 deletion(-)
>> 
>> diff --git a/libavutil/dovi_meta.h b/libavutil/dovi_meta.h
>> index e10332f8d7..e168075a24 100644
>> --- a/libavutil/dovi_meta.h
>> +++ b/libavutil/dovi_meta.h
>> @@ -91,6 +91,8 @@ typedef struct AVDOVIRpuDataHeader {
>>     uint8_t spatial_resampling_filter_flag;
>>     uint8_t el_spatial_resampling_filter_flag;
>>     uint8_t disable_residual_flag;
>> +    uint8_t ext_mapping_idc_0_4; /* extended base layer inverse mapping indicator */
>> +    uint8_t ext_mapping_idc_5_7; /* reserved */
>> } AVDOVIRpuDataHeader;
> 
> What value ranges have you seen for this indicator? Is it possible that
> some values would extend the RPU in other ways, adding more bits that we
> need to parse?

So far I've only seen two sets of values. 

The samples from the iPhone:

ext_mapping_idc[4:0] = 0
ext_mapping_idc[7:5] = 0

The samples from Xiaomi and Oppo:

ext_mapping_idc[4:0] = 1
ext_mapping_idc[7:5] = 4

I don't have any additional information on what the possible range of values could be so far.
As far as I can tell it has no impact on the size of the subsequent fields, at least for what I've encountered so far.


> 
> Maybe we should enforce this to be a well-known value just to be on the
> safe side, until we receive public documentation on its purpose.
> 

I think to avoid being brittle we should allow the entire range of values for now until we know better, and just ensure it roundtrips correctly (which I've verified by running the validator on the 10.4 output transcoded from 8.4 input).

Once we track down more info we can try to add more validation on top of it.

- Cosmin