[vlc-devel] [PATCH v2 5/5] libvlc: media: set WITH_ASSOCIATED_MEDIA option to preparser

[Alexandre Janniaux]

Hi,

On Sat, Feb 08, 2020 at 04:35:49PM +0200, Rémi Denis-Courmont wrote:
> Le perjantaina 7. helmikuuta 2020, 23.04.49 EET Alexandre Janniaux a écrit :
> > When a LibVLC client associates multiple inputs to a media through the
> > input slave mechanism, it should expect that all associated media get
> > preparsed so that listing tracks and elementary stream ids give
> > a comprehensive result.
> >
> > To achieve this, always set the WITH_ASSOCIATED_MEDIA when requesting
> > a preparsing from the LibVLC API.
>
> For tracks, that's very agreeable. For meta-data, not so much: You probably
> don't want the meta of an external subtitle file clobbering the meta of the
> main input. It's not clear if this controls onl the first case, or both, which
> IMO would be wrong.

Indeed, but I'm not sure whether fixing this can be part of
this patchset and if it should be done before or after. Also
it would work for most usual cases but would mainly break
when associating multiple audio files together or an audio
file with a video file and different metadata, which is my
use case but probably not the usual one as this mechanism is
mainly targeting video + subtitle.

It needs fixing though. It's unclear to me whether other
metadata should be parsed but provided differently to the
libvlc client or not parsed.

The first case is probably best fitted for a more general
use case, but would need a different libvlc_media_get_meta
so as to have different meta store per input, which would
mean this should probably go into libvlc 4.

If you believe this is a blocking issue for this patchset,
I can try providing a fix for the issue with meta.

>
> Also, if it's always set, then I'm not exactly clear why it needs a flag.
>

The flag is always set for libvlc client, as requested in the
previous review, but not for libvlccore users. I'm not sure
I can generalize to libvlccore without breaking other users
(preparsing, medialibrary, thumbnailing, though I didn't
check those).

As I mainly want to fix libvlc for this issue, I'd prefer
not to include libvlccore change into this patchset,
especially since I'm not a user of this API in libvlccore.
If it is deemed unecessary by other clients, it could be
removed without changing libvlc new behaviour and libvlc
API/ABI and the resulting patches will be clearer to
interpret.

Regards,
--
Alexandre Janniaux
Videolabs

> > ---
> >  lib/media.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/lib/media.c b/lib/media.c
> > index f045c729d2..bd40fc388a 100644
> > --- a/lib/media.c
> > +++ b/lib/media.c
> > @@ -801,6 +801,9 @@ static int media_parse(libvlc_media_t *media, bool
> > b_async, if (parse_flag & libvlc_media_do_interact)
> >              parse_scope |= META_REQUEST_OPTION_DO_INTERACT;
> >
> > +        /* Always preparse associated media when using libvlc. */
> > +        parse_scope |= META_REQUEST_OPTION_WITH_ASSOCIATED_MEDIA;
> > +
> >          ret = libvlc_MetadataRequest(libvlc, item, parse_scope,
> >                                       &input_preparser_callbacks, media,
> >                                       timeout, media);
>
>
> --
> Реми Дёни-Курмон
> http://www.remlab.net/
>
>
>
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