ASS decoder also requires ass_split.o to be compiled.

libavcodec/Makefile

@@ -76,7 +76,7 @@ OBJS-$(CONFIG_AMV_DECODER)             += sp5xdec.o mjpegdec.o mjpeg.o
 OBJS-$(CONFIG_ANM_DECODER)             += anm.o
 OBJS-$(CONFIG_ANSI_DECODER)            += ansi.o cga_data.o
 OBJS-$(CONFIG_APE_DECODER)             += apedec.o
-OBJS-$(CONFIG_ASS_DECODER)             += assdec.o ass.o
+OBJS-$(CONFIG_ASS_DECODER)             += assdec.o ass.o ass_split.o
 OBJS-$(CONFIG_ASS_ENCODER)             += assenc.o ass.o
 OBJS-$(CONFIG_ASV1_DECODER)            += asv1.o mpeg12data.o
 OBJS-$(CONFIG_ASV1_ENCODER)            += asv1.o mpeg12data.o