On Fri, 18 May 2018 11:54:52 -0700
Richard Shaffer <rshaf...@tunein.com> wrote:
> On Fri, May 18, 2018 at 2:54 AM, wm4 <nfx...@googlemail.com> wrote:
>
> > On Thu, 17 May 2018 20:49:42 -0700
> > rshaf...@tunein.com wrote:
> >
> > > From: Richard Shaffer <rshaf...@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, ×tamp, &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.
> >
>
> Yes, that's a good point. If timestamps are in ID3 tags, they'll be at the
> start of every segment. I can think of several ways to handle that:
>
> Option 1: Technically it is updated metadata, so mark it as updated. Leave
> it up to the API caller to figure out whether they care about it or not.
>
> Option 2: Filter out timestamp ID3 frames, and only mark it as updated if
> some other ID3 tag or frame is present.
>
> Option 3: Compare the new metadata with the last seen metadata, and only
> set the event flag if something besides the timestamp has actually changed.
> That would filter out false updates for the API consumer, but I'm pretty
> sure nothing else that handles metadata updates works this way.
>
> Any thoughts? Personally I'd lean towards 1 or 2.
2 sounds good.
>
> >
> > >
> > > 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.
> >
>
> That's not the only reason this is wrong. I'll fix it.
Oh, didn't notice.
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