[FFmpeg-user] libswscale maximum image size

[bn]

n generating thumbnails I notice that libswscale bails out on some larger images:

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ffmpeg -i verylarge.jpg -s 160x120 -f image2 thumb.jpg
...
[scale @ 0x1d1b8e0] w:2744 h:4472 fmt:gray -> w:160 h:120 fmt:yuvj420p flags:0x4
Error opening filters!
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browsing git I can see "swscale: remove VOF/VOFW" committed in May 
but it's not clear from the diff (to me anyway) how size-limits are enforced now and what to patch if I want an increase.

thanks