[FFmpeg-devel] [PATCH] avcodec/cbs_av1: fix range of values for Mastering Display Color Volume Metadata OBUs

Mark Thompson sw at jkqxz.net
Sat Mar 23 18:06:35 EET 2019


On 23/03/2019 14:48, James Almer wrote:
> On 3/23/2019 9:46 AM, Mark Thompson wrote:
>> On 21/03/2019 18:37, James Almer wrote:
>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>> ---
>>>  libavcodec/cbs_av1_syntax_template.c | 10 +++++-----
>>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/libavcodec/cbs_av1_syntax_template.c b/libavcodec/cbs_av1_syntax_template.c
>>> index 48f4fab514..93bba1e5ad 100644
>>> --- a/libavcodec/cbs_av1_syntax_template.c
>>> +++ b/libavcodec/cbs_av1_syntax_template.c
>>> @@ -1637,15 +1637,15 @@ static int FUNC(metadata_hdr_mdcv)(CodedBitstreamContext *ctx, RWContext *rw,
>>>      int err, i;
>>>  
>>>      for (i = 0; i < 3; i++) {
>>> -        fcs(16, primary_chromaticity_x[i], 0, 50000, 1, i);
>>> -        fcs(16, primary_chromaticity_y[i], 0, 50000, 1, i);
>>> +        fbs(16, primary_chromaticity_x[i], 1, i);
>>> +        fbs(16, primary_chromaticity_y[i], 1, i);
>>>      }
>>>  
>>> -    fc(16, white_point_chromaticity_x, 0, 50000);
>>> -    fc(16, white_point_chromaticity_y, 0, 50000);
>>> +    fb(16, white_point_chromaticity_x);
>>> +    fb(16, white_point_chromaticity_y);
>>>  
>>>      fc(32, luminance_max, 1, MAX_UINT_BITS(32));
>>> -    fc(32, luminance_min, 0, current->luminance_max >> 6);
>>> +    fc(32, luminance_min, 0, (current->luminance_max << 6) - 1);
>>
>> << 6 in uint32_t can overflow.
> 
> What do you suggest? Casting to uint64_t will get the value clipped when
> passed to ff_cbs_read_unsigned() and potentially result in a failed
> range check.

Does something like
FFMIN(((uint64_t)current->luminance_max << 6) - 1, MAX_UINT_BITS(32))
do the right thing?

>>
>> Given the confusion in the previous value, maybe a comment to explain where the upper bound for min is coming from too?
>>
>>>  
>>>      return 0;
>>>  }
>>>
>> LGTM with that.
>>


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