avformat/flvenc: Do not allow creating h263/mpeg4 in flv without unofficial format extensions being enabled.

Found-by: Jean-Baptiste Kempf <jb@videolan.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/flvenc.c

@@ -221,6 +221,18 @@ static int flv_write_header(AVFormatContext *s)
                        avcodec_get_name(enc->codec_id), i);
                 return AVERROR(EINVAL);
             }
+            if (enc->codec_id == AV_CODEC_ID_MPEG4 ||
+                enc->codec_id == AV_CODEC_ID_H263) {
+                int error = enc->strict_std_compliance > FF_COMPLIANCE_UNOFFICIAL;
+                av_log(s, error ? AV_LOG_ERROR : AV_LOG_WARNING,
+                       "Codec %s is not supported in the official FLV specification,\n", avcodec_get_name(enc->codec_id));
+
+                if (error) {
+                    av_log(s, AV_LOG_ERROR,
+                           "use vstrict=-1 / -strict -1 to use it anyway.\n");
+                    return AVERROR(EINVAL);
+                }
+            }
             break;
         case AVMEDIA_TYPE_AUDIO:
             if (audio_enc) {