On 4/1/2021 7:07 AM, Anton Khirnov wrote:
Quoting James Almer (2021-03-25 14:37:20)
On 3/25/2021 8:55 AM, Nicolas George wrote:
Same situation as av_add_index_entry(). And if you look at the signature
of the (3) function in my last proposal, i kept the av_index_* namespace
free precisely in case a new API in the future needs to be added for
this reason, for both add() and get(). One that could work directly with
the AVIndexEntry struct after the internal entries array was redesigned,
perhaps using AVTreeNode, so returned pointers or entries are safer to
handle.
On the topic of av_add_index_entry() - is there any reason that function
should be public? Seems like it's internal-use only.
We could deprecate it and make it internal, if it's not used by callers.
It may have been added back when things were devised as being more user
controlled, which ultimately didn't happen, or just made public without
giving it much thought.
Option (4) has the obvious practical drawback that misusing the API
causes undefined behavior.
The constraint of using a pointer immediately on risk of undefined
behavior is actually a frequent one, in FFmpeg but also in C at large:
gethosbtyname, localtime, etc.
For me, that makes it approximately on par with the risk of messing the
order of the many arguments.
Which leaves more typing, NULL checks overhead or useless variables
(still more typing).
It is tiny, I have no trouble admitting, but it is tiny in favor of one
solution.
If you do not agree with these estimates, please explain exactly where.
I don't know if you remember how in this one imgutils patch i sent some
time ago i was against functions with tons of output parameters, because
i considered it ugly and typical of enterprise software API. That hasn't
changed. But here, being the exact counterpart of an existing add()
function put it above the other approach i dislike slightly more of
returning an internal pointer and not being able to tell the user just
what may invalidate it.
If some other developer wants to chime in and comment which approach they
prefer, then that would be ideal.
FWIW in this specific case exporting a short-lived pointer seems less
problematic than the other options.
But on the other hand I wonder about exporting AVIndexEntry exactly as
is internally. Are all these fields useful or even meaningful to
external callers?
Perhaps we could make a new struct that would export only those fields
people actually use. And have the new API return a pointer to something
like AVFormatInternal.index_entry_for_the_caller.
There are five fields, pos, timestamp, flags, size, and min_distance.
The first three are the most important, with timestamps and flags IMO
being the only useful ones for users building their own index entry list
for example to display each seek point to the user in a player's seek bar.
Pos doesn't seem like it would be useful outside of the internal seeking
methods, size seems to be the least useful of them all, and min_distance
i can't say, since it probably is mainly useful to also for the internal
seeking methods.
So instead of making a new struct, or build a second array internally,
we could maybe just return those two fields?
Also a naming note - I'd prefer the function names to start with
avformat, so it's clearer where they belong. "index" can mean many
different things.
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
