[FFmpeg-devel] [PATCH] avformat/hls: Properly expose intercepted ID3 tags to the API.

[wm4]

On Thu, 17 May 2018 20:49:42 -0700
rshaffer at tunein.com wrote:

> From: Richard Shaffer <rshaffer at tunein.com>
> 
> The HLS demuxer will process any ID3 tags at the beginning of a segment in
> order to obtain timestamp data. However, when this data was parsed on a second
> or subsequent segment, the updated metadata would be discarded. This change
> preserves the data and also sets the AVSTREAM_EVENT_FLAG_METADATA_UPDATED
> event flag when appropriate.
> ---
>  libavformat/hls.c | 34 +++++++++++++++++++---------------
>  1 file changed, 19 insertions(+), 15 deletions(-)
> 
> diff --git a/libavformat/hls.c b/libavformat/hls.c
> index 3d4f7f2647..3e2edb3484 100644
> --- a/libavformat/hls.c
> +++ b/libavformat/hls.c
> @@ -982,18 +982,8 @@ static void parse_id3(AVFormatContext *s, AVIOContext *pb,
>  }
>  
>  /* Check if the ID3 metadata contents have changed */
> -static int id3_has_changed_values(struct playlist *pls, AVDictionary *metadata,
> -                                  ID3v2ExtraMetaAPIC *apic)
> +static int id3_has_changed_values(struct playlist *pls, ID3v2ExtraMetaAPIC *apic)
>  {
> -    AVDictionaryEntry *entry = NULL;
> -    AVDictionaryEntry *oldentry;
> -    /* check that no keys have changed values */
> -    while ((entry = av_dict_get(metadata, "", entry, AV_DICT_IGNORE_SUFFIX))) {
> -        oldentry = av_dict_get(pls->id3_initial, entry->key, NULL, AV_DICT_MATCH_CASE);
> -        if (!oldentry || strcmp(oldentry->value, entry->value) != 0)
> -            return 1;
> -    }
> -
>      /* check if apic appeared */
>      if (apic && (pls->ctx->nb_streams != 2 || !pls->ctx->streams[1]->attached_pic.data))
>          return 1;
> @@ -1019,6 +1009,15 @@ static void handle_id3(AVIOContext *pb, struct playlist *pls)
>      int64_t timestamp = AV_NOPTS_VALUE;
>  
>      parse_id3(pls->ctx, pb, &metadata, &timestamp, &apic, &extra_meta);
> +    ff_id3v2_parse_priv_dict(&metadata, &extra_meta);
> +    av_dict_copy(&pls->ctx->metadata, metadata, 0);
> +    /*
> +     * If we've handled any ID3 metadata here, it's not going to be seen by the
> +     * sub-demuxer. In the case that we got here because of an IO call during
> +     * hls_read_header, this will be cleared. Otherwise, it provides the
> +     * necessary hint to hls_read_packet that there is new metadata.
> +     */
> +    pls->ctx->event_flags |= AVFMT_EVENT_FLAG_METADATA_UPDATED;

Can't ID3 tags happen in large quantities with that ID3 timestamp hack
(curse whoever invented it)? Wouldn't that lead to a large number of
redundant events? Not sure though, I don't have the overview.

>  
>      if (timestamp != AV_NOPTS_VALUE) {
>          pls->id3_mpegts_timestamp = timestamp;
> @@ -1037,12 +1036,10 @@ static void handle_id3(AVIOContext *pb, struct playlist *pls)
>              /* demuxer not yet opened, defer picture attachment */
>              pls->id3_deferred_extra = extra_meta;
>  
> -        ff_id3v2_parse_priv_dict(&metadata, &extra_meta);
> -        av_dict_copy(&pls->ctx->metadata, metadata, 0);
>          pls->id3_initial = metadata;
>  
>      } else {
> -        if (!pls->id3_changed && id3_has_changed_values(pls, metadata, apic)) {
> +        if (!pls->id3_changed && id3_has_changed_values(pls, apic)) {
>              avpriv_report_missing_feature(pls->ctx, "Changing ID3 metadata in HLS audio elementary stream");
>              pls->id3_changed = 1;
>          }
> @@ -1939,8 +1936,15 @@ static int hls_read_header(AVFormatContext *s)
>           * Copy any metadata from playlist to main streams, but do not set
>           * event flags.
>           */
> -        if (pls->n_main_streams)
> +        if (pls->n_main_streams) {
>              av_dict_copy(&pls->main_streams[0]->metadata, pls->ctx->metadata, 0);
> +            /*
> +             * If we've intercepted metadata, we will have set this event flag.
> +             * Clear it to avoid confusion, since otherwise we will flag it as
> +             * new metadata on the next call to hls_read_packet.
> +             */
> +            pls->ctx->event_flags = ~AVFMT_EVENT_FLAG_METADATA_UPDATED;

I think ~(unsigned)AVFMT_EVENT_... would be preferable for maximum
correctness.

> +        }
>  
>          add_metadata_from_renditions(s, pls, AVMEDIA_TYPE_AUDIO);
>          add_metadata_from_renditions(s, pls, AVMEDIA_TYPE_VIDEO);