restore run-time bitrate commands for VP8 and H263/MPEG4 encoder.

src/videofilters/videoenc.c

@@ -941,6 +941,7 @@ static int enc_set_br(MSFilter *f, void *arg) {
 	if (s->av_context.codec != NULL) {
 		/* Encoding is already ongoing, do not change video size, only bitrate. */
 		s->vconf.required_bitrate = br;
+		enc_set_configuration(f, &s->vconf);
 	} else {
 		MSVideoConfiguration best_vconf = ms_video_find_best_configuration_for_bitrate(s->vconf_list, br);
 		enc_set_configuration(f, &best_vconf);

src/videofilters/vp8.c

@@ -347,6 +347,7 @@ static int enc_set_br(MSFilter *f, void*data) {
 	if (s->ready) {
 		/* Encoding is already ongoing, do not change video size, only bitrate. */
 		s->vconf.required_bitrate = br;
+		enc_set_configuration(f, &s->vconf);
 	} else {
 		MSVideoConfiguration best_vconf = ms_video_find_best_configuration_for_bitrate(s->vconf_list, br);
 		enc_set_configuration(f, &best_vconf);