[FFmpeg-devel] SW's Patchsets Overview

[softworkz .]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Marton
> Balint
> Sent: Mittwoch, 2. April 2025 21:45
> To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] SW's Patchsets Overview
> 
> 
> 
> On Wed, 2 Apr 2025, softworkz . wrote:
> 
> > Hello everybody,
> >
> > with freshly gained push access rights, I want to act responsibly and
> > carefully, and also avoid unexpected surprises so I'm not going to
> rush
> > things. Due to that change, I thought it might be good to post an
> > overview of the patchsets I am intending to push in the near future:
> 
> Thanks for the heads up.
> 
> [...]
> 
> > avutil/log: Replace addresses in log output with simple ids
> >
> > GitHub:    https://github.com/ffstaging/FFmpeg/pull/59
> > Patchwork:
> https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=14094
> 

Hi Marton,

thanks a lot for looking at the patchset.

> To be honest, I don't like this at all. You duplicate a lot of code from
> avutil/log, and the implementation has quite a few problems, some of
> them not really fixable.

Originally, this was a patch against avutil/log. Nicolas objected that it was adding global state and Hendrik (and Nicolas) suggested that I should to this in fftools only - outside of the libs, in a was that fftools get their own logging implementation - with the potential of being able to do other things in the future that wouldn't make sense in the lib code.
Letting fftools have their own logging implementation of can of course only start from a copy in order to retain existing behavior. On top of that I applied that little change then.


> - creating object IDs in the order the objects log something (what if
> they do not? What if it depends on loglevel?)
> - tracking object IDs based on their address - objects are
>    allocated and removed at runtime, it is possible that an address will be
>    re-used for a different object later on

The Ids are not meant to have much more value than the addresses currently shown - with an important difference: They are short and remain the same on repeated execution. Plus: they are counted by AVClass, that give a little additional value, but since they are just "indexing" the addresses, they are in fact prone to the same shortcomings like the addresses themselves, meaning that a re-assignment might give you the same id for something different and also different addresses (in consequence the IDs as well) can reference the same thing (e.g. with buffer refs).

> - linear search of addresses. A long ffmpeg process can constantly
> create
>    objects during runtime, eventually completely depleting the pool and
>    causing an extensive search for all future logs.

I have considered that case. There is a hard limit from when on no IDs are assigned anymore (all zeros).


> So overall I don't think it's worth pursuing this, especially since most
> users won't care neither about the ID, nor about the address...

Let me give two examples of where I find it useful to have those IDs:

On startup decoders can be initialized multiple times, like first for probing and then for transcoding. Or when there are multiple streams of the same type (codec), the log messages can be confusing when the log output from several identical ones gets mixed up. Being able to see "which is which" is quite of value at times.

HW Device context can also get initialized multiple times and knowing which one has shut down already and which hasn't - is helpful. Also, in case of complex filtergraphs with multiple derived and reverse-derived hw contexts, one can quickly get lost in understanding the logs.


That being said - I don't want to insist on those IDs. We could also just hide the addresses (activatable by a log flag) and I'd still be happy about being able to do logfile diffs in the future without trouble 😊

In that case, the change could also be made just in avutil/log. Probably also depends on what the consensus would be regarding the value of fftools having their own logging implementation - or rather not?

I'm open for either direction.

Thank you,
sw