[FFmpeg-devel] [PATCH] libavformat/aac: Parse ID3 tags between ADTS frames.

[wm4]

On Thu,  1 Feb 2018 18:37:45 -0800
rshaffer at tunein.com wrote:

> From: Richard Shaffer <rshaffer at tunein.com>
> 
> While rare, ID3 tags may be inserted between ADTS frames. This change enables
> parsing them and setting the appropriate metadata updated event flag.
> ---
> I have encountered a streaming provider that I must support which does this.
> There are indications that it isn't totally off the wall, and that it does
> happen in the wild:
> * https://www.w3.org/TR/mse-byte-stream-format-mpeg-audio/
>   (See specifically sections 3 and 4.)
> * https://github.com/video-dev/hls.js/issues/508
> 
> That being said, the providers that do this are in the minority. It seems most
> streaming providers will do one of the following:
>  1. If using .aac segments inside of HLS, use the #EXTINF for text metadata and
>     use an ID3 tag at the head of the segment for things like timing metadata.
>  2. If streaming raw AAC over HTTP, use Icy metadata.
> 
> Aside from comments on the code, I'd be interested in any opinion about whether
> this is something that should or should not be supported in libavformat.
> 
> Thanks,
> 
> -Richard
> 
>  libavformat/aacdec.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/aacdec.c b/libavformat/aacdec.c
> index 36d558ff54..5ec706bdc7 100644
> --- a/libavformat/aacdec.c
> +++ b/libavformat/aacdec.c
> @@ -22,8 +22,10 @@
>  
>  #include "libavutil/intreadwrite.h"
>  #include "avformat.h"
> +#include "avio_internal.h"
>  #include "internal.h"
>  #include "id3v1.h"
> +#include "id3v2.h"
>  #include "apetag.h"
>  
>  #define ADTS_HEADER_SIZE 7
> @@ -116,13 +118,52 @@ static int adts_aac_read_header(AVFormatContext *s)
>      return 0;
>  }
>  
> +static int handle_id3(AVFormatContext *s, AVPacket *pkt)
> +{
> +    AVDictionary *metadata = NULL;
> +    AVIOContext ioctx;
> +    ID3v2ExtraMeta *id3v2_extra_meta = NULL;
> +    int ret;
> +
> +    ret = av_append_packet(s->pb, pkt, ff_id3v2_tag_len(pkt->data) - pkt->size);
> +    if (ret < 0) {
> +        av_packet_unref(pkt);
> +        return ret;
> +    }
> +
> +    ffio_init_context(&ioctx, pkt->data, pkt->size, 0, NULL, NULL, NULL, NULL);
> +    ff_id3v2_read_dict(&ioctx, &metadata, ID3v2_DEFAULT_MAGIC, &id3v2_extra_meta);
> +    if ((ret = ff_id3v2_parse_priv_dict(&metadata, &id3v2_extra_meta)) < 0)
> +        goto error;
> +
> +    if (metadata) {
> +        if ((ret = av_dict_copy(&s->metadata, metadata, 0)) < 0)
> +            goto error;
> +        s->event_flags |= AVFMT_EVENT_FLAG_METADATA_UPDATED;
> +    }
> +
> +error:
> +    av_packet_unref(pkt);
> +    ff_id3v2_free_extra_meta(&id3v2_extra_meta);
> +    av_dict_free(&metadata);
> +
> +    return ret;
> +}
> +
>  static int adts_aac_read_packet(AVFormatContext *s, AVPacket *pkt)
>  {
>      int ret, fsize;
>  
> -    ret = av_get_packet(s->pb, pkt, ADTS_HEADER_SIZE);
> +    ret = av_get_packet(s->pb, pkt, FFMAX(ID3v2_HEADER_SIZE, ADTS_HEADER_SIZE));
> +
> +    if (ret >= ID3v2_HEADER_SIZE && ff_id3v2_match(pkt->data, ID3v2_DEFAULT_MAGIC)) {
> +        if ((ret = handle_id3(s, pkt)) >= 0)
> +            ret = av_get_packet(s->pb, pkt, ADTS_HEADER_SIZE);
> +    }
> +
>      if (ret < 0)
>          return ret;
> +
>      if (ret < ADTS_HEADER_SIZE) {
>          av_packet_unref(pkt);
>          return AVERROR(EIO);
> @@ -139,7 +180,7 @@ static int adts_aac_read_packet(AVFormatContext *s, AVPacket *pkt)
>          return AVERROR_INVALIDDATA;
>      }
>  
> -    ret = av_append_packet(s->pb, pkt, fsize - ADTS_HEADER_SIZE);
> +    ret = av_append_packet(s->pb, pkt, fsize - pkt->size);
>      if (ret < 0)
>          av_packet_unref(pkt);
>  

Applied. (I hope this is the most recent version...)