[FFmpeg-devel] [PATCH] Extract QP from h264 encoded videos

[James Almer]

On 7/29/2019 11:19 PM, Juan De León wrote:
> On Mon, Jul 29, 2019 at 12:48 PM Mark Thompson <sw at jkqxz.net> wrote:
> 
>> This doesn't belong in the commit message.
>>
>> What does belong here would be some commentary on why you want this
>> feature.
>>
> Here is the, somewhat outdated, design document, this should explain it.
> https://docs.google.com/document/d/1WClt3EqhjwdGXhEw386O0wfn3IBQ1Ib-_5emVM1gbnA/edit?usp=sharing
> <https://docs.google.com/document/d/1WClt3EqhjwdGXhEw386O0wfn3IBQ1Ib-_5emVM1gbnA/edit#>
> In short the purpose is to implement an API to extract QP and calculate min
> max and average.
> 
>> +    int x, y;
>>
>> How do these values interact with cropping?
> 
> I'm not sure I understand, could you elaborate?
> 
>> +    AVQuantizationParams *qp_arr;
>>
>> Side-data is reference counted, so how is this pointer managed?  More
>> genrally, it would probably help to explain exactly how this is allocated
>> and who will be responsible for freeing it.
>>
> The idea is to allocate the memory, for AVQuantizationParamsArray and the
> necessary number of AVQuantizationParams, in a single buffer that can be
> freed when the side data is freed.

Side data, or more specifically, any AVBufferRef, must be a flat array.
You can't have pointers to some other allocated buffer within them since
you can't really control their lifetime.