nullenc: Use the wrapped avframe pseudo-encoder

libavformat/nullenc.c

@@ -30,7 +30,7 @@ AVOutputFormat ff_null_muxer = {
     .name              = "null",
     .long_name         = NULL_IF_CONFIG_SMALL("raw null video"),
     .audio_codec       = AV_NE(AV_CODEC_ID_PCM_S16BE, AV_CODEC_ID_PCM_S16LE),
-    .video_codec       = AV_CODEC_ID_RAWVIDEO,
+    .video_codec       = AV_CODEC_ID_WRAPPED_AVFRAME,
     .write_packet      = null_write_packet,
-    .flags             = AVFMT_NOFILE | AVFMT_NOTIMESTAMPS | AVFMT_RAWPICTURE,
+    .flags             = AVFMT_NOFILE | AVFMT_NOTIMESTAMPS,
 };