[FFmpeg-devel] [PATCH 28/42] lavc/hevc/ps: implement SPS parsing for nuh_layer_id>0

[James Almer]

On 9/3/2024 6:39 AM, Anton Khirnov wrote:
> Quoting James Almer (2024-08-30 04:52:39)
>> On 8/27/2024 12:05 PM, Anton Khirnov wrote:
>>> @@ -1167,16 +1167,26 @@ int ff_hevc_parse_sps(HEVCSPS *sps, GetBitContext *gb, unsigned int *sps_id,
>>>        }
>>>    
>>>        sps->max_sub_layers = get_bits(gb, 3) + 1;
>>> +    multi_layer_ext = nuh_layer_id > 0 &&
>>> +                      sps->max_sub_layers == HEVC_MAX_SUB_LAYERS + 1;
>>> +    if (multi_layer_ext) {
>>> +        if (!sps->vps)
>>> +            return AVERROR(EINVAL);
>>> +
>>> +        sps->max_sub_layers = sps->vps->vps_max_sub_layers;
>>> +    }
>>>        if (sps->max_sub_layers > HEVC_MAX_SUB_LAYERS) {
>>
>> Not strictly related to this patch, but sps->max_sub_layers should
>> always be <= vps->vps_max_sub_layers (see F.7.4.3.2.1). So the presence
>> of vps should be checked for.
>>
>>>            av_log(avctx, AV_LOG_ERROR, "sps_max_sub_layers out of range: %d\n",
>>>                   sps->max_sub_layers);
>>>            return AVERROR_INVALIDDATA;
>>>        }
>>>    
>>> +    if (!multi_layer_ext) {
>>>        sps->temporal_id_nesting = get_bits(gb, 1);
>>
>> Similarly (not strictly related to this patch), this needs to be 1 if
>> sps->max_sub_layers is 0 or if vps->vps_temporal_id_nesting_flag is 1.
>>
>>>    
>>>        if ((ret = parse_ptl(gb, avctx, 1, &sps->ptl, sps->max_sub_layers)) < 0)
>>>            return ret;
>>> +    }
>>
>> (Actually related this time) If multi_layer_ext is true,
>> sps->temporal_id_nesting needs to be set to
>> vps->vps_temporal_id_nesting_flag when sps->max_sub_layers > 1, or
>> hardcoded to 1 if it's 1.
> 
> Honestly this feels like pointless churn. We don't support any of this
> temporal id stuff in the decoder, so why bother?

I see it used in videotoolbox.c and vulkan_hevc.c, so imo better make 
sure it's set right, just in case.

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