[FFmpeg-devel] [PATCH] avutil/eval: add function to track variable use

[Michael Niedermayer]

On Tue, Nov 05, 2019 at 06:35:54PM +0530, Gyan wrote:
> 
> 
> On 05-11-2019 03:55 pm, Michael Niedermayer wrote:
> >On Tue, Nov 05, 2019 at 10:13:52AM +0530, Gyan wrote:
> >>
> >>On 05-11-2019 04:35 am, Michael Niedermayer wrote:
> >>>On Sun, Nov 03, 2019 at 11:14:25AM +0530, Gyan wrote:
> >>>>Helps better identification of expr eval failures.
> >>>>
> >>>>Gyan
> >>>>  eval.c    |   21 +++++++++++++++++++++
> >>>>  eval.h    |   10 ++++++++++
> >>>>  version.h |    4 ++--
> >>>>  3 files changed, 33 insertions(+), 2 deletions(-)
> >>>>3dd142baa0144fd324eb9da8a9932cfd7ab2cd98  0001-avutil-eval-add-function-to-track-variable-use.patch
> >>>> From 19bce329464676f071707b99575f80e5abe1cd4c Mon Sep 17 00:00:00 2001
> >>>>From: Gyan Doshi <ffmpeg at gyani.pro>
> >>>>Date: Sat, 2 Nov 2019 20:16:42 +0530
> >>>>Subject: [PATCH] avutil/eval: add function to track variable use
> >>>>
> >>>>Helps avoid multiple evals of cross-referenced expressions
> >>>>and catch the use of non-applicable variables with respect
> >>>>to eval or special mode in filters
> >>>Maybe you should provide more details of the use case of this, maybe
> >>>with an example. Because it seems not completely obvious
> >>An example of a cross-referenced expression would be 'y=x+rand(10)'.
> >>Normally in filters, X would be evaluated first, then Y, then X again. The
> >>2nd eval of X will overwrite the first and can generate a different value.
> >>With this func, we can avoid the 2nd eval.
> >>
> >>I'm in the process of modifying the scale filter to allow 'n', 't', 'pos'
> >>variables in frame eval mode (it already supports dynamic output based on
> >>incoming frame changes) and I would like to catch their presence in init
> >>mode, since av_expr_eval will fail. Now, it can also fail due to circularly
> >>referenced expressions e.g. 'x=y+10' and 'y=x+10' and there's no way to
> >>detect whether it's this case or if inapplicable variables have been used.
> >please add this (or similar information) to the commit message
> 
> Done.
> 
> Thanks,
> Gyan

>  eval.c    |   21 +++++++++++++++++++++
>  eval.h    |   10 ++++++++++
>  version.h |    4 ++--
>  3 files changed, 33 insertions(+), 2 deletions(-)
> 740f6166ddb4b1a581aee7c34edd05d328265df1  v2-0001-avutil-eval-add-function-to-track-variable-use.patch
> From 2931fa96b8e7f80581ded280907655753e54def0 Mon Sep 17 00:00:00 2001
> From: Gyan Doshi <ffmpeg at gyani.pro>
> Date: Sat, 2 Nov 2019 20:16:42 +0530
> Subject: [PATCH v2 1/2] avutil/eval: add function to track variable use

i think the patch is ok but i think nicolas wants to wait
with pushing this until there is a 2nd patch which uses the new
function

Thanks

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
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