avcodec: add AVCodecContext.frame_num as 64 bit variant to frame_number

Frame counters can overflow relatively easily (INT_MAX number of frames is
slightly more than 1 year for 60 fps content), so make sure we use 64 bit
values for them.

Also deprecate the old 32 bit frame_number attribute.

Signed-off-by: Marton Balint <cus@passwd.hu>

fftools/ffmpeg.c

@@ -2115,7 +2115,7 @@ static int decode(InputStream *ist, AVCodecContext *avctx,
             fd      = (FrameData*)frame->opaque_ref->data;
             fd->pts = frame->pts;
             fd->tb  = avctx->pkt_timebase;
-            fd->idx = avctx->frame_number - 1;
+            fd->idx = avctx->frame_num - 1;
         }
 
         *got_frame = 1;