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

[Arpi]

Hi,

this code is better than nothing but far from being perfect and far from
being what the comment/commitmsg says.

iso 8859-1 charset are 32..255 and not 1..127 what the check verifies.
a correct check and conversion although requires utf8 decoding, which
is a bit tricky, especially if you check for bougus data, for example
the string-termitor zero byte after an utf8 prefix...

A'rpi

> ffmpeg | branch: master | Anton Khirnov <anton at khirnov.net> | Sat Feb  5
> 22:20:13 2011 +0100| [4a3556542d249718d3a7f59586ea1acc0a2d5e77] |
> committer: Michael Niedermayer
> 
> mp3enc: write ISO8859-1 instead of UTF-16 when possible
> 
> Signed-off-by: Ronald S. Bultje <rsbultje at gmail.com>
> (cherry picked from commit 5a6de4e7e8d81169be9b6909b71e42a9ece59a82)
> 
> > http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=4a3556542d249718d3a7f59586ea1acc0a2d5e77
> ---
> 
>  libavformat/mp3enc.c |   12 ++++++++++++
>  1 files changed, 12 insertions(+), 0 deletions(-)
> 
> diff --git a/libavformat/mp3enc.c b/libavformat/mp3enc.c
> index b2c0a7e..5921ded 100644
> --- a/libavformat/mp3enc.c
> +++ b/libavformat/mp3enc.c
> @@ -77,6 +77,12 @@ static void id3v2_put_size(AVFormatContext *s, int size)
>      put_byte(s->pb, size       & 0x7f);
>  }
>  
> +static int string_is_ascii(const uint8_t *str)
> +{
> +    while (*str && *str < 128) str++;
> +    return !*str;
> +}
> +
>  /**
>   * 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 +98,12 @@ 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) &&
> +        (!str2 || string_is_ascii(str2)))
> +        enc = ID3v2_ENCODING_ISO8859;
> +
>      put_byte(dyn_buf, enc);
>      if (enc == ID3v2_ENCODING_UTF16BOM) {
>          put_le16(dyn_buf, 0xFEFF);      /* BOM */
> 
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