On Fri, Dec 22, 2023 at 3:57 PM Mark Filipak <markfilipak.i...@gmail.com> wrote: > > Hi Devin, > > On 12/22/23 15:14, Devin Heitmueller wrote: > > On Fri, Dec 22, 2023 at 2:38 PM Mark Filipak <markfilipak.i...@gmail.com> > > wrote: > >> > >> This page: https://ffmpeg.org/ffmpeg-utils.html > >> 'says' this: > >> > >> "The following abbreviations are recognized: > >> "‘sntsc’ > >> " 640x480" > >> > >> What is it? I'm not aware that any such thing exists. > > > > It's NTSC with square pixels... > > How do you go from 720x480 to 640x480 without throwing away 80 pixels per > line? > Normally, 720x480 decodes to 720x540.
I would encourage you to do some reading up on "pixel aspect ratio" and "non-square pixels" Briefly, the number of lines is fixed, since they correspond to the scanlines put out to the CRT raster. However the width of the video is determined on how often the analog waveform was sampled. The display aspect ratio is 4:3, and if you have square pixels that would mean you have a resolution of 640x480. However it was common to capture 720 samples per line to improve image quality, and as a result the actual pixels are rectangular (i.e. slightly taller than they are wide). If you don't treat the pixels as non-square, you end up with a display aspect ratio which is greater than 4:3, and the image looks horizontally stretched. > > > (as opposed to the more common pixel > > aspect ratio of 10:11 found with 720x480). > > > > Devin > > Umm... 10:11? What is that? See above. The pixel isn't square. It's actually a rectangle which is 10% taller than it is wide. Even worse, you can have 720x480 video with a display aspect ratio of 16:9 (i.e. standard definition widescreen). In this case the pixel aspect ratio is going to be 40:33. Yeah, this is all a huge PITA. I'm very happy that with HD resolutions they just decided to make all pixels square. Devin -- Devin Heitmueller, Senior Software Engineer LTN Global Communications o: +1 (301) 363-1001 w: https://ltnglobal.com e: devin.heitmuel...@ltnglobal.com _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
