example:

AVPixelFormat pixFmts[] = { AV_PIX_FMT_RGB24, AV_PIX_FMT_RGBA };
int loss = 0;
AVPixelFormat best = avcodec_find_best_pix_fmt_of_list(pixFmts, AV_PIX_FMT_BGRA, 1, &loss);

best is AV_PIX_FMT_RGB24. But AV_PIX_FMT_RGBA is better.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>