[FFmpeg-devel] [PATCH] mp3enc: write ISO8859-1 instead of UTF-16 when possible

[Anton Khirnov]

---
 libavformat/mp3enc.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/libavformat/mp3enc.c b/libavformat/mp3enc.c
index b2c0a7e..dd01caa 100644
--- a/libavformat/mp3enc.c
+++ b/libavformat/mp3enc.c
@@ -77,6 +77,16 @@ static void id3v2_put_size(AVFormatContext *s, int size)
     put_byte(s->pb, size       & 0x7f);
 }
 
+static int string_is_ascii(const uint8_t *str)
+{
+    int ret = 1;
+    do {
+        if (*str > 127)
+            ret = 0;
+    } while (*str++);
+    return ret;
+}
+
 /**
  * Write a text frame with one (normal frames) or two (TXXX frames) strings
  * according to encoding (only UTF-8 or UTF-16+BOM supported).
@@ -92,6 +102,12 @@ static int id3v2_put_ttag(AVFormatContext *s, const char *str1, const char *str2
     if (url_open_dyn_buf(&dyn_buf) < 0)
         return AVERROR(ENOMEM);
 
+    /* check if the strings are ASCII-only and use UTF16 only if
+     * they're not */
+    if (enc == ID3v2_ENCODING_UTF16BOM && string_is_ascii(str1))
+        if ((str2 && string_is_ascii(str2)) || !str2)
+            enc = ID3v2_ENCODING_ISO8859;
+
     put_byte(dyn_buf, enc);
     if (enc == ID3v2_ENCODING_UTF16BOM) {
         put_le16(dyn_buf, 0xFEFF);      /* BOM */
-- 
1.7.2.3