avcodec: make vismv option as flag types

This allows for example -vismv pf+bf+bb instead of -vismv 7.

libavcodec/options_table.h

@@ -252,7 +252,7 @@ static const AVOption avcodec_options[] = {
 {"buffers", "picture buffer allocations", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_BUFFERS }, INT_MIN, INT_MAX, V|D, "debug"},
 {"thread_ops", "threading operations", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_THREADS }, INT_MIN, INT_MAX, V|A|D, "debug"},
 {"nomc", "skip motion compensation", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_NOMC }, INT_MIN, INT_MAX, V|A|D, "debug"},
-{"vismv", "visualize motion vectors (MVs)", OFFSET(debug_mv), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, V|D, "debug_mv"},
+{"vismv", "visualize motion vectors (MVs)", OFFSET(debug_mv), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, INT_MAX, V|D, "debug_mv"},
 {"pf", "forward predicted MVs of P-frames", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_VIS_MV_P_FOR }, INT_MIN, INT_MAX, V|D, "debug_mv"},
 {"bf", "forward predicted MVs of B-frames", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_VIS_MV_B_FOR }, INT_MIN, INT_MAX, V|D, "debug_mv"},
 {"bb", "backward predicted MVs of B-frames", 0, AV_OPT_TYPE_CONST, {.i64 = FF_DEBUG_VIS_MV_B_BACK }, INT_MIN, INT_MAX, V|D, "debug_mv"},