ffmpeg: raise level for message printed in case of auto-select pixel format

Increase visibility, in order to decrease troubleshooting for
users generating non playable H.264 content.
Signed-off-by: Carl Eugen Hoyos <cehoyos@ag.or.at>

ffmpeg.c

@@ -2336,7 +2336,7 @@ static int transcode_init(void)
                 if (!strncmp(ost->enc->name, "libx264", 7) &&
                     codec->pix_fmt == AV_PIX_FMT_NONE &&
                     ost->filter->filter->inputs[0]->format != AV_PIX_FMT_YUV420P)
-                    av_log(NULL, AV_LOG_INFO,
+                    av_log(NULL, AV_LOG_WARNING,
                            "No pixel format specified, %s for H.264 encoding chosen.\n"
                            "Use -pix_fmt yuv420p for compatibility with outdated media players.\n",
                            av_get_pix_fmt_name(ost->filter->filter->inputs[0]->format));