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

[Juan De León]

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Here is the, somewhat outdated, design document, this should explain it.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.


> > +enum QP_ARR_INDEXES_FOR_H264 {
> > +        QP_H264 = 0,            // qp value
>
> What value specifically does this refer to?  QP_Y or QP'_Y for the given
> block?
>
It refers to the final QP of the block, not the delta.
Also Added a field for chroma QP, thanks!


> What is the proposed consumer of this?  It might help if you provided that
> as well (a filter?).
>
The filter is incomplete but I can submit what I have so far if needed to
give more context.
The document explains it better.
https://docs.google.com/document/d/1WClt3EqhjwdGXhEw386O0wfn3IBQ1Ib-_5emVM1gbnA/edit?usp=sharing