[FFmpeg-devel] Ignore duplicate ID3 tags if vorbis tags exist

Oops, I don't know what went wrong, but now it seems to work.

I've attached the working patched, sorry!


Le 26/01/2017 à 02:12, Michael Niedermayer a écrit :
> On Wed, Jan 25, 2017 at 08:33:53PM +0100, Paul Arzelier wrote:
>> Hi all,
>>
>> Would it be possible to continue the discussion began there ?
>> http://ffmpeg.org/pipermail/ffmpeg-devel/2015-February/168248.html
>>
>> The current behavior of FFmpeg when it comes to manage FLAC tags with
>> both vorbis tags and ID3 tags is to append both, which leads to, for
>> example, "Artist: Pink Floyd;Pink Floyd" in FFprobe. This is not a
>> desired output: as the XIPH faq says about FLAC
>> (https://xiph.org/flac/faq.html):
>> "FLAC has it's own native tagging system which is identical to that of
>> Vorbis. They are called alternately "FLAC tags" and "Vorbis comments".
>> It is the only tagging system required and guaranteed to be supported by
>> FLAC implementations.
>> Out of convenience, the reference decoder knows how to skip ID3 tags so
>> that they don't interfere with decoding. But you should not expect any
>> tags beside FLAC tags to be supported in applications; some
>> implementations may not even be able to decode a FLAC file with ID3 tags."
>>
>> This issue was also submitted here https://trac.ffmpeg.org/ticket/3799,
>> but still discuted in the above thread.
>> Ben Boeckel made the attached patch (which I edited a bit to fit FFmpeg
>> last version), which fixes the issue.
>> The problem that remained was that many other files could have
>> irrelevant id3v2 tags, not only Vorbis/FLAC files, so another more
>> global patch may be needed to fix that definitely.
>>
>> So, do you think Ben's patch could be merged "as-is", or does it only
>> raise more questions?
>>
>> Regards,
>> Paul
>>
> the attached patch is corrupted:
>
> Applying: Fixed behavior when id3 tags were found on FLAC files
> error: corrupt patch at line 58
> Patch failed at 0001 Fixed behavior when id3 tags were found on FLAC files
> The copy of the patch that failed is found in: .git/rebase-apply/patch
> When you have resolved this problem, run "git am --continue".
> If you prefer to skip this patch, run "git am --skip" instead.
> To restore the original branch and stop patching, run "git am --abort".
>
>
> [...]
>
>
>
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On Thu, 26 Jan 2017 11:08:45 +0100
Paul Arzelier <paul.arzelier@free.fr> wrote:

> From bb5dc73c42ad2e0bffd7e38fac18c6f01ec05ab3 Mon Sep 17 00:00:00 2001
> From: Paul Arzelier <paul.arzelier@free.fr>
> Date: Thu, 26 Jan 2017 11:04:44 +0100
> Subject: [PATCH] Fixed behavior when id3 tags were found on FLAC files
> Originally-by: Ben Boeckel <mathstuf@gmail.com>
> ---
>  libavformat/flacdec.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/libavformat/flacdec.c b/libavformat/flacdec.c
> index 66baba5922..869936621b 100644
> --- a/libavformat/flacdec.c
> +++ b/libavformat/flacdec.c
> @@ -48,6 +48,7 @@ static int flac_read_header(AVFormatContext *s)
>      int ret, metadata_last=0, metadata_type, metadata_size, found_streaminfo=0;
>      uint8_t header[4];
>      uint8_t *buffer=NULL;
> +    int has_id3 = 0;
>      FLACDecContext *flac = s->priv_data;
>      AVStream *st = avformat_new_stream(s, NULL);
>      if (!st)
> @@ -63,6 +64,22 @@ static int flac_read_header(AVFormatContext *s)
>          return 0;
>      }
>  
> +    if (av_dict_count(s->metadata)) {
> +         /* XXX: Is there a better way to parse this out? ID3 parsing is done
> +         * all the way out in avformat_open_input. */
> +         has_id3 = 1;
> +    }
> +
> +    if (has_id3) {
> +         int level = AV_LOG_WARNING;
> +         if (s->error_recognition & AV_EF_COMPLIANT)
> +              level = AV_LOG_ERROR;
> +         av_log(s, level, "Spec-compliant flac files do not support ID3 tags.\n");
> +         if (s->error_recognition & AV_EF_EXPLODE)
> +              return AVERROR_INVALIDDATA;
> +    }
> +
> +
>      /* process metadata blocks */
>      while (!avio_feof(s->pb) && !metadata_last) {
>          if (avio_read(s->pb, header, 4) != 4)
> @@ -173,8 +190,16 @@ static int flac_read_header(AVFormatContext *s)
>              }
>              /* process supported blocks other than STREAMINFO */
>              if (metadata_type == FLAC_METADATA_TYPE_VORBIS_COMMENT) {
> +                AVDictionary *other_meta = NULL;
>                  AVDictionaryEntry *chmask;
>  
> +                if (has_id3) {
> +                    av_log(s, AV_LOG_VERBOSE, "FLAC found with ID3 and vorbis tags; ignoring ID3 tags also provided by vorbis.\n");
> +
> +                    other_meta = s->metadata;
> +                    s->metadata = NULL;
> +                }
> +
>                  ret = ff_vorbis_comment(s, &s->metadata, buffer, metadata_size, 1);
>                  if (ret < 0) {
>                      av_log(s, AV_LOG_WARNING, "error parsing VorbisComment metadata\n");
> @@ -182,6 +207,11 @@ static int flac_read_header(AVFormatContext *s)
>                      s->event_flags |= AVFMT_EVENT_FLAG_METADATA_UPDATED;
>                  }
>  
> +                if (other_meta) {
> +                    av_dict_copy(&s->metadata, other_meta, AV_DICT_DONT_OVERWRITE);
> +                    av_dict_free(&other_meta);
> +                }
> +
>                  /* parse the channels mask if present */
>                  chmask = av_dict_get(s->metadata, "WAVEFORMATEXTENSIBLE_CHANNEL_MASK", NULL, 0);
>                  if (chmask) {

I feel like there should be a more general solution.

ID3v2 tags are read by common code, and such tags are supported by
basically all file formats in libavformat due to the way it's
implemented.

This fixes it for FLAC only. Are we going to duplicate this for every
format?

I suggest reading id3 tags into a separate dict instead, and then
copying it in libavformat/utils.c after read_header if the demuxer
hasn't set any tags.