avcodec/utils: Check that channel count is valid in avcodec_open2();

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/utils.c

@@ -1617,6 +1617,12 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
         } else if (avctx->channel_layout) {
             avctx->channels = av_get_channel_layout_nb_channels(avctx->channel_layout);
         }
+        if (avctx->channels < 0) {
+            av_log(avctx, AV_LOG_ERROR, "Specified number of channels %d is not supported\n",
+                    avctx->channels);
+            ret = AVERROR(EINVAL);
+            goto free_and_end;
+        }
         if(avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
             if (avctx->width <= 0 || avctx->height <= 0) {
                 av_log(avctx, AV_LOG_ERROR, "dimensions not set\n");