[x264-devel] Re: HD Encoding

[Tuukka Toivonen]

On Thu, 10 Feb 2005, Loren Merritt wrote:

>> source material in 1920x1080i format (29.97 FPS).  The problem is, with x264
>> you have to represent the resolution in a multiple of 16, which means the
>> height must be represented as 1072, which creates for a not so nice encode.
> True, not nice for HDTV with fixed aspect ratios. But while I haven't rerun 
> compression tests in H.264 (I_4x4 and UMV might make a difference), cropping 
> and/or scaling to mod16 was the most efficient method (in terms of PSNR per 
> bitrate) in MPEG-4 ASP.

Scaling - sure, since it tends to lose detail (probably even when scaling 
slightly upwards).
Cropping - you lose picture information on boundaries
Expanding larger (e.g. mencoder -vf expand) - you get black borders, not 
nice

I think the ideal solution might be for the encoder to internally expand
the image into larger size by extrapolating the edge pixels, encode 
using the slightly larger image size, but then enable frame_cropping_flag
and set correspondingly frame_crop_right_offset and 
frame_crop_bottom_offset -- a smart decoder could then crop the decoded 
image into the original size.

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