[Libav-user] MPEG2 4:2:2 encoding in 4:3 sample_aspect_ratio
alexcohn at netvision.net.il
Sun Mar 18 09:27:42 CET 2012
On Fri, Mar 16, 2012 at 09:42, <francesco at bltitalia.com> wrote:
> Ok, thanks for the answer. So If I have well understood, in this case I sould
> insert 1:1 that means no frame distortion. With this settings if I start
> from a 4:3 frame (720x576) I obtain the same frame form in output. Right ?
There is a nice explanation of ffmpeg -aspect parameter (which is
mapped to .sample_aspect_ratio) http://howto-pages.org/ffmpeg/
MPEG2 video allows for anamorphic display. This means that the aspect
ratio (width divided by the height) of the physical picture displayed
on-screen can be different from the ratio obtained by dividing the
pixel-width of the image by its pixel-height. This has to be built in
to the video specification used with DVDs because, regardless of
whether we're viewing a movie in old 4:3 aspect ratio or a movie in
16:9 widescreen format, the pixel size of the digital image is still
720x480 for an NTSC DVD (720x576 for PAL). The image is in fact
stretched such that its aspect ratio is as specified by the "-aspect"
option. This usually involves stretching it only along its width or
along its height, hence the name "anamorphic".
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