[Mp4-tech] aspect_ratio_idc

[John Cox]

Hi
In Mpeg-II land you get a display aspect rate which tells you what shape
the picture is.  In AVC land you get a sample aspect ratio giving you
the shape of a sample.  To get from the shape of a sample to the shape
of the display you use <width in samples> * <sample width>:<height in
samples> * <sample height>.  Having got that ratio you can then see
which of your predefined ratios it most closely matches.
John Cox
SJ Consulting Ltd
>I don't understand what the encoding of the aspect_ratio_idc means.  I've got 
>a 352x240 NTSC sample, meaning it's going to be scaled up to a 4:3 720x480 
>image.  In MPEG-2 the sequence header would contain an encoding for "4:3", 
>but in h.264 I see the value 7 which means, according to the table in the 
>spec, is 10:11 and might represent a 352x480 4:3 frame without overscan or a 
>480x480 16:9 frame with horizontal overscan.  Okay, so what am I supposed to 
>do with this?  How do I know the sample is 4:3?
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