"Ronald S. Bultje" <rsbul...@gmail.com> skrev: (6 mars 2016 14:37:25 CET) >Hi, > >On Sun, Mar 6, 2016 at 7:37 AM, Mats Peterson < >matsp888-at-yahoo....@ffmpeg.org> wrote: > >> 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....@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. > > >See the implementation [1]. If not seekable, and the seek is forward, >it >fills buffer until it reaches that position. If not seekable and seek >is >backward but fits in buffer, it works as expected by changing buffer >index. >Etc. See also avio_tell [2]. Line 230 of avio_seek tells you the >shortcut >that makes this all work without calls to fseek/ftell. > >Ronald > >[1] https://ffmpeg.org/doxygen/trunk/aviobuf_8c_source.html#l00209 >[2] https://ffmpeg.org/doxygen/trunk/avio_8h_source.html#l00447 >_______________________________________________ >ffmpeg-devel mailing list >ffmpeg-devel@ffmpeg.org >http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
OK, thanks. -- Mats Peterson http://matsp888.no-ip.org/~mats/ _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
