On Tue, Apr 17, 2018 at 08:32:57AM +0300, Timo Teras wrote: > On Tue, 17 Apr 2018 01:02:43 +0200 > Michael Niedermayer <mich...@niedermayer.cc> wrote: > > > On Mon, Apr 16, 2018 at 07:56:34PM +0200, Marton Balint wrote: > > > > > > On Mon, 16 Apr 2018, Timo Teras wrote: > > > > > > >On Sun, 15 Apr 2018 16:42:01 +0200 (CEST) > > > >Marton Balint <c...@passwd.hu> wrote: > > > > > > > >>On Sun, 15 Apr 2018, Timo Teräs wrote: > > > >> > > > >>> Calculate DAR with assumed SAR 1:1 when SAR is undefined. Same > > > >>> assumption is done in ffplay to create the play window. Usually > > > >>> DAR is more useful metadata than SAR when e.g. choosing which > > > >>> media of multiple versions to use to fit the display. > > > >> > > > >>I don't think it's good idea to generally assume 1:1 > > > >>display_aspect_ratio for every undefined sample aspect ratio. It > > > >>depends heavily on your actual use case. If MOV/MP4 specifies that > > > >>1:1 SAR should be used, then maybe you should fix > > > >>av_guess_sample_aspect_ratio instead, and return 1:1 there if the > > > >>format context is MOV/MP4. You may add a demuxer (AVFMT) flag to > > > >>signal that such behaviour should be used, and > > > >>av_guess_sample_aspect_ratio can check for that demuxer flag. > > > > > > > >Looking at code, av_guess_sample_aspect_ratio() is used only in > > > >ffplay and ffprobe. > > > > > > > >ffplay implicitly assumes undefined SAR is 1:1 to create the > > > >playback window properly; this happens in calculate_display_rect() > > > >when "bad" aspect_ratio is reset to 1.0. > > > > > > > >I would expect same logic would have been useful in ffprobe. This > > > >would help to report back to user what ffplay is going to do with > > > >the video. Or at least give a hint on how to categorize the clip. > > > >SAR 1:1 is pretty good guess for most formats. > > > > > > I really don't see why don't you fix your application instead which > > > parses ffprobe output? If you see N/A aspect ratio, use 1:1. > > > > > > To be frank, I am not sure if ffprobe should use > > > av_guess_aspect_ratio when it displays stream metadata. It is only > > > there now to av_reduce the aspect > > > > > ratios and to sanitize some invalid aspect ratios to 0/1. FFprobe's > > > job is to return stream metadata as is, not to make guesses. > > > > a very minor somewhat on topic nitpick, 0/0 would be mathamtically > > more correct as unknown than 0/1. If one doesnt immedeatly see why, > > one can look at width/height vs height/width to see one of many > > reasons why > > See my earlier patch that changes it to report as "N/A". This is what
i meant the function. Which cannot output N/A as it outputs a "rational number" not a string. and for such numbers 0/0 closer represents undefined than 0/1 in a mathematical sense [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB "I am not trying to be anyone's saviour, I'm trying to think about the future and not be sad" - Elon Musk
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