avformat/mpl2dec: skip BOM when probing

Fixes #5442.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavformat/mpl2dec.c

@@ -23,6 +23,8 @@
  * MPL2 subtitles format demuxer
  */
 
+#include "libavutil/intreadwrite.h"
+
 #include "avformat.h"
 #include "internal.h"
 #include "subtitles.h"
@@ -39,6 +41,9 @@ static int mpl2_probe(AVProbeData *p)
     const unsigned char *ptr = p->buf;
     const unsigned char *ptr_end = ptr + p->buf_size;
 
+    if (AV_RB24(ptr) == 0xefbbbf)
+        ptr += 3;
+
     for (i = 0; i < 2; i++) {
         if (sscanf(ptr, "[%"SCNd64"][%"SCNd64"]%c", &start, &end, &c) != 3 &&
             sscanf(ptr, "[%"SCNd64"][]%c",          &start,       &c) != 2)
@@ -83,6 +88,9 @@ static int mpl2_read_header(AVFormatContext *s)
     st->codecpar->codec_type = AVMEDIA_TYPE_SUBTITLE;
     st->codecpar->codec_id   = AV_CODEC_ID_MPL2;
 
+    if (avio_rb24(s->pb) != 0xefbbbf)
+        avio_seek(s->pb, -3, SEEK_CUR);
+
     while (!avio_feof(s->pb)) {
         char line[4096];
         char *p = line;