Print a warning if a subtitle demuxer changes utf16 to utf8.

This does not fix anything but gives users a chance to
know that they must not pass -sub_charenc UTF-16 to ffmpeg.

Fixes ticket #4059.

libavformat/assdec.c

@@ -112,7 +112,7 @@ static int ass_read_header(AVFormatContext *s)
     int res = 0;
     AVStream *st;
     FFTextReader tr;
-    ff_text_init_avio(&tr, s->pb);
+    ff_text_init_avio(s, &tr, s->pb);
 
     st = avformat_new_stream(s, NULL);
     if (!st)

libavformat/realtextdec.c

@@ -65,7 +65,7 @@ static int realtext_read_header(AVFormatContext *s)
     char c = 0;
     int res = 0, duration = read_ts("60"); // default duration is 60 seconds
     FFTextReader tr;
-    ff_text_init_avio(&tr, s->pb);
+    ff_text_init_avio(s, &tr, s->pb);
 
     if (!st)
         return AVERROR(ENOMEM);

libavformat/samidec.c

@@ -54,7 +54,7 @@ static int sami_read_header(AVFormatContext *s)
     char c = 0;
     int res = 0, got_first_sync_point = 0;
     FFTextReader tr;
-    ff_text_init_avio(&tr, s->pb);
+    ff_text_init_avio(s, &tr, s->pb);
 
     if (!st)
         return AVERROR(ENOMEM);

libavformat/srtdec.c

@@ -87,7 +87,7 @@ static int srt_read_header(AVFormatContext *s)
     AVStream *st = avformat_new_stream(s, NULL);
     int res = 0;
     FFTextReader tr;
-    ff_text_init_avio(&tr, s->pb);
+    ff_text_init_avio(s, &tr, s->pb);
 
     if (!st)
         return AVERROR(ENOMEM);

libavformat/subtitles.c

@@ -24,7 +24,7 @@
 #include "libavutil/avassert.h"
 #include "libavutil/avstring.h"
 
-void ff_text_init_avio(FFTextReader *r, AVIOContext *pb)
+void ff_text_init_avio(void *s, FFTextReader *r, AVIOContext *pb)
 {
     int i;
     r->pb = pb;
@@ -45,13 +45,16 @@ void ff_text_init_avio(FFTextReader *r, AVIOContext *pb)
             r->buf_pos += 3;
         }
     }
+    if (s && (r->type == FF_UTF16LE || r->type == FF_UTF16BE))
+        av_log(s, AV_LOG_WARNING,
+               "UTF16 is automatically converted to UTF8, do not specify a character encoding\n");
 }
 
 void ff_text_init_buf(FFTextReader *r, void *buf, size_t size)
 {
     memset(&r->buf_pb, 0, sizeof(r->buf_pb));
     ffio_init_context(&r->buf_pb, buf, size, 0, NULL, NULL, NULL, NULL);
-    ff_text_init_avio(r, &r->buf_pb);
+    ff_text_init_avio(NULL, r, &r->buf_pb);
 }
 
 int64_t ff_text_pos(FFTextReader *r)

libavformat/subtitles.h

@@ -49,14 +49,16 @@ typedef struct {
  * Initialize the FFTextReader from the given AVIOContext. This function will
  * read some bytes from pb, and test for UTF-8 or UTF-16 BOMs. Further accesses
  * to FFTextReader will read more data from pb.
+ * If s is not NULL, the user will be warned if a UTF-16 conversion takes place.
  *
  * The purpose of FFTextReader is to transparently convert read data to UTF-8
  * if the stream had a UTF-16 BOM.
  *
+ * @param s Pointer to provide av_log context
  * @param r object which will be initialized
  * @param pb stream to read from (referenced as long as FFTextReader is in use)
  */
-void ff_text_init_avio(FFTextReader *r, AVIOContext *pb);
+void ff_text_init_avio(void *s, FFTextReader *r, AVIOContext *pb);
 
 /**
  * Similar to ff_text_init_avio(), but sets it up to read from a bounded buffer.