[Libav-user] Problem with swscale, data is partially discarded?

[Max Göttner - d.stream]

Hi!

The following code excerpt scales inFrame to outFrame.

Let the resolution of inFrame be 1024x768.

 

Scaling to resolutions with changed outWidth (800, 320, 
) while keeping the
outHeight at 768 delivers a correct outFrame.

However if I change the values of outHeight < 768, the resulting image will
have the correct resolution, but all lines that correspond to the lines in
inFrame with number  (768-outHeight)
768 are black.

In the case of scaling(1024x768 -> 512 x 384) the lower half of the picture
would be black.

 

Here’s an excerpt from my code

 

//decode frame

avcodec_decode_video2 (CodecCtx, inFrame , &got_picture_ptr, &pkt);

 

// scale frame

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,
NULL);

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

 

After that outFrame->data seems to be allocated correctly but with the last
part of the array beeing 0.

 

Is this a known bug, or do I miss something?

Thanks for help.

 

Max.

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