Re: [FFmpeg-devel] [PATCH 2/2] lavf/id3v2dec: support multiple values and TIPL frames

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

rcombs:
> Fixes https://trac.ffmpeg.org/ticket/6949
> 
> Ordinary text frames in ID3v2 are allowed to have multiple
> (null-separated) values. This technically isn't allowed in TXXX,
> but it's used in practice by Picard, and supporting it is harmless.
> 
> TIPL/IPL (Involved People List) and TMCL (Musician Credits List) work
> similarly to TXXX, but alternate key-value-key-value.
> ---
>  libavformat/id3v2.c | 49 ++++++++++++++++++++++++++-------------------
>  1 file changed, 28 insertions(+), 21 deletions(-)
> 
> diff --git a/libavformat/id3v2.c b/libavformat/id3v2.c
> index 191a305ffb..667105e9f9 100644
> --- a/libavformat/id3v2.c
> +++ b/libavformat/id3v2.c
> @@ -321,8 +321,12 @@ static void read_ttag(AVFormatContext *s, AVIOContext *pb, int taglen,
>                        AVDictionary **metadata, const char *key)
>  {
>      uint8_t *dst;
> -    int encoding, dict_flags = AV_DICT_DONT_OVERWRITE | AV_DICT_DONT_STRDUP_VAL;
> +    uint8_t *dst_key = NULL;
> +    int encoding, dict_flags = AV_DICT_MULTIKEY | AV_DICT_DONT_STRDUP_VAL;
>      unsigned genre;
> +    int count = 0;
> +    int is_tipl = !(strcmp(key, "TIPL") && strcmp(key, "TMCL") &&
> +                    strcmp(key, "IPL"));
>  
>      if (taglen < 1)
>          return;
> @@ -330,30 +334,33 @@ static void read_ttag(AVFormatContext *s, AVIOContext *pb, int taglen,
>      encoding = avio_r8(pb);
>      taglen--; /* account for encoding type byte */
>  
> -    if (decode_str(s, pb, encoding, &dst, &taglen) < 0) {
> -        av_log(s, AV_LOG_ERROR, "Error reading frame %s, skipped\n", key);
> -        return;
> -    }
> -
> -    if (!(strcmp(key, "TCON") && strcmp(key, "TCO"))                         &&
> -        (sscanf(dst, "(%d)", &genre) == 1 || sscanf(dst, "%d", &genre) == 1) &&
> -        genre <= ID3v1_GENRE_MAX) {
> -        av_freep(&dst);
> -        dst = av_strdup(ff_id3v1_genre_str[genre]);
> -    } else if (!(strcmp(key, "TXXX") && strcmp(key, "TXX"))) {
> -        /* dst now contains the key, need to get value */
> -        key = dst;
> +    while (taglen > 1) {
>          if (decode_str(s, pb, encoding, &dst, &taglen) < 0) {
>              av_log(s, AV_LOG_ERROR, "Error reading frame %s, skipped\n", key);
> -            av_freep(&key);
>              return;
>          }
> -        dict_flags |= AV_DICT_DONT_STRDUP_KEY;
> -    } else if (!*dst)
> -        av_freep(&dst);
>  
> -    if (dst)
> -        av_dict_set(metadata, key, dst, dict_flags);
> +        count++;
> +
> +        if (!(strcmp(key, "TCON") && strcmp(key, "TCO"))                         &&
> +            (sscanf(dst, "(%d)", &genre) == 1 || sscanf(dst, "%d", &genre) == 1) &&
> +            genre <= ID3v1_GENRE_MAX) {
> +            av_freep(&dst);
> +            dst = av_strdup(ff_id3v1_genre_str[genre]);
> +        } else if (!(strcmp(key, "TXXX") && strcmp(key, "TXX")) ||
> +                   (is_tipl && (count & 1))) {
> +            /* dst now contains the key, need to get value */
> +            av_free(dst_key);
> +            key = dst_key = dst;
> +            continue;
> +        } else if (!*dst)
> +            av_freep(&dst);
> +
> +        if (dst)
> +            av_dict_set(metadata, key, dst, dict_flags);
> +    }
> +
> +    av_free(dst_key);
>  }
>  
>  static void read_uslt(AVFormatContext *s, AVIOContext *pb, int taglen,
> @@ -1039,7 +1046,7 @@ static void id3v2_parse(AVIOContext *pb, AVDictionary **metadata,
>                      pbx = &pb_local.pub; // read from sync buffer
>                  }
>  #endif
> -            if (tag[0] == 'T')
> +            if (tag[0] == 'T' || !strcmp(tag, "IPL"))
>                  /* parse text tag */
>                  read_ttag(s, pbx, tlen, metadata, tag);
>              else if (!memcmp(tag, "USLT", 4))

From avformat.h:

"Keys are unique; there can never be 2 tags with the same key. This is
also meant semantically, i.e., a demuxer should not knowingly produce
several keys that are literally different but semantically identical.
E.g., key=Author5, key=Author6. In this example, all authors must be
placed in the same tag."

If this requirement did not exist, I would have fixed #6949 and #9641
long ago.

- Andreas
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