[FFmpeg-devel] [PATCH] avformat/avienc: Remove unneeded seekable tests

[Mats Peterson]

On 03/06/2016 01:29 PM, Ronald S. Bultje wrote:
> Hi Mats,
>
> On Sun, Mar 6, 2016 at 6:51 AM, Mats Peterson <
> matsp888-at-yahoo.com at ffmpeg.org> wrote:
>
>> On 03/06/2016 12:09 PM, Michael Niedermayer wrote:
>>
>> Once again, why are these tests unneeded?
>
>
> You shouldn't send the same message 5x within 2 seconds. Please be patient.
>
> Why are they unneeded? Imagine this situation:
>
> ----
> int a;
>
> if (condition)
>      a = create_a();
>
> [..]
>
> if (condition)
>      do_something_with_a(a);
> ----
>
> versus:
>
> ----
> int a = create_a();
>
> [..]
>
> if (condition)
>      do_something_with_a(a);
> ----
>
> Oddly, both codes do exactly the same thing, assuming they don't change
> global state. In this case, avio_tell() shouldn't change global state, that
> is, we're assuming that it will not cause bitstream corruption simply
> because it's unseekable, which is a fair assumption.
>
> On the positive side, with that assumption, code fragment #2 is much
> simpler than #1, which is why the patch is net positive.
>
> Ronald
> _______________________________________________
> ffmpeg-devel mailing list


Well, that part I understand. It's for simplification purposes.

By the way, I just noticed that avio_tell() (and avio_seek() will work 
on stdout as well. That's the part I *don't* understand: How can they 
work on an "officially" unseekable stream like stdout, when ftell() and 
lseek() won't? Is it due to the buffering in FFmpeg? And where's the 
limit where a normally "unseekable stream" like stdout is no longer 
seekable with avio_seek()? Hope you understand what I mean.

Mats