[Libav-user] Problem with swscale, bottom lines are black if height is reduced.

Max Göttner - d.stream max.goettner at dstream.de
Thu Dec 22 15:23:32 CET 2011


I couldn’t find a solution yet,  but maybe someone else has an idea about
this problem:

Scaling via sws_scale() works fine, if I extend width and height, or if I
compress width. However if I compress the height, scaling is done, but
bottom lines are black. 

Example scaling from 800x600 -> 800x400: the lowest third of the frame is

Thanks for any suggestion. 



// scale frame code excerpt

static struct SwsContext* img_convert_ctx;

avpicture_alloc ((AVPicture*)outFrame, outPixFmt, outWidth, outHeight);

img_convert_ctx = sws_getContext (CodecCtx->width, CodecCtx->height,
CodecCtx->pix_fmt, outWidth, outHeight, outPixFmt, sws_flags, NULL, NULL,

sws_scale(img_convert_ctx, inFrame->data, inFrame->linesize, 0, outHeight,
outFrame->data, outFrame->linesize);

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