Merge commit '0a51c7d4'

* commit '0a51c7d4':
  prores: Set the bits_per_coded_sample for alpha pix_fmt
Merged-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/proresenc_kostya.c

@@ -1163,6 +1163,7 @@ static av_cold int encode_init(AVCodecContext *avctx)
             av_log(avctx, AV_LOG_ERROR, "alpha bits should be 0, 8 or 16\n");
             return AVERROR(EINVAL);
         }
+        avctx->bits_per_coded_sample = 32;
     } else {
         ctx->alpha_bits = 0;
     }