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avformat/id3v2enc: use UTF-16 in id3v2.3 APIC frame only if non-ASCII

This makes the encoding of picture descriptions consistent with the
encoding of other text id3 tags and works better with iTunes, which
does not display pictures with some UTF-16 picture descriptions
(including a UTF-16 empty string, i.e. BOM + terminator). It also
saves a few bytes.

Example:
ffmpeg -f lavfi -i sine=b=4 -f lavfi -i smptebars -map 0:a -map 1:v \
-codec:a libmp3lame -codec:v mjpeg -id3v2_version 3 \
-metadata:s:v comment="Cover (front)" -t 3 -y out.mp3

This example does not set a picture description (-metadata:s:v title=)
so an empty string is written in the id3v2.3 APIC frame. Without this
patch, UTF-16 is used and the cover art does not display in iTunes.
With the patch the cover art is displayed. (Note that iTunes does not
display or have a way to set picture descriptions, only the picture
itself, but nevertheless has trouble skipping some UTF-16 descriptions.)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Mark Harris authored on 2013/08/11 09:03:11
Showing 1 changed files

libavformat/id3v2enc.c

History View file @ 4ccafac

@@ -295,6 +295,10 @@ int ff_id3v2_write_apic(AVFormatContext *s, ID3v2EncContext *id3, AVPacket *pkt)
                          if ((e = av_dict_get(st->metadata, "title", NULL, 0)))
                              desc = e->value;
                     +    /* use UTF16 only for non-ASCII strings */
                     +    if (enc == ID3v2_ENCODING_UTF16BOM && string_is_ascii(desc))
                     +        enc = ID3v2_ENCODING_ISO8859;
+                    +
                          /* start writing */
                          if (avio_open_dyn_buf(&dyn_buf) < 0)
                              return AVERROR(ENOMEM);