@@ -75,6 +75,7 @@ typedef struct GifState {

     AVCodecContext *avctx;

     int keyframe;

+    int keyframe_ok;

     int trans_color;    /**< color value that is used instead of transparent color */

 } GifState;

@@ -472,6 +473,7 @@ static int gif_decode_frame(AVCodecContext *avctx, void *data, int *got_frame, A

     }

     if (s->keyframe) {

+        s->keyframe_ok = 0;

         if ((ret = gif_read_header1(s)) < 0)

             return ret;

@@ -489,7 +491,13 @@ static int gif_decode_frame(AVCodecContext *avctx, void *data, int *got_frame, A

         s->picture.pict_type = AV_PICTURE_TYPE_I;

         s->picture.key_frame = 1;

+        s->keyframe_ok = 1;

     } else {

+        if (!s->keyframe_ok) {

+            av_log(avctx, AV_LOG_ERROR, "cannot decode frame without keyframe\n");

+            return AVERROR_INVALIDDATA;

+        }

+

         if ((ret = avctx->reget_buffer(avctx, &s->picture)) < 0) {

             av_log(avctx, AV_LOG_ERROR, "reget_buffer() failed\n");

             return ret;