On 07/01/2015 18:46, Philip Langdale wrote: > On Wed, 7 Jan 2015 12:13:25 +0100 > Nicolas George <geo...@nsup.org> wrote: > >> Can you explain the 1024? >> >> Anyway, I would suggest to use lavu's rational functions: >> >> AVRational dar = av_mul_q(avctx->sample_aspect_ratio, >> av_make_q(avctx->width, avctx->height)); >> av_reduce(&dar.num, &dar.den, dar.num, dar.den, MAX); >> nvenc_ctx->nvenc_cfg.darWidth = 1024 * dar.num; >> nvenc_ctx->nvenc_cfg.darHeight = 1045 * dar.den; >> >> (including the *1.02 in the 1024 constant to avoid floating point >> operations, but I am very suspicious about that 1.02) >> >> Regards, >> > > Honestly, I don't understand what the encoder is doing at this point. > The 1.02 seems to be the 'correct' scale factor for a PAL DVD,
http://web.archive.org/web/20100826080627/www.bbc.co.uk/commissioning/tvbranding/picturesize.shtml says 1.094 > but is > incorrect for anything else. I used 1024 to avoid the floating point > problem, but you are right that pre-multiplication is a better way to > handle that. Right now I'm playing around with an NTSC DVD and I can't > find the right magic to stop it mangling the aspect ratio. Where 'PAL' (I use the term loosely to imply 25 702x576 interlaced pictures in a 720x576 frame) is: 768x576 active square pixels in a 788x576 square pixel frame for 4:3 or 1024x576 active square pixels in a 1050x576 square pixel frame for 16:9 for the full frame 'NTSC' (loosely 30000/1001 710.85x486 interlaced pictures in a 720x486 frame) is approximately: 648x486 active square pixels in a 656.34x486 square pixel frame for 4:3 or 864x486 active square pixels in a 875.12x486 square pixel frame for 16:9 Although, I'm not sure that information is going to help you :-( > At this point, I'm not convinced that darWidth and darHeight are even > representing the display presentation size at all. Hopefully Agatha can > understand what's going on here. > > --phil > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
