[Icecast-dev] MetaData Update for FLAC and OPUS

[Philipp Schafft]

Good afternoon,


On Tue, 2019-08-13 at 14:26 +0200, bn at radio42.com wrote:
> I am using the standard Xiph.org FLAC encoder, but I couldn't find any option to update the meta-data mid-stream.
> Also the FLAC spec says, that it defines VORBIS_COMMENT as the only way to transmit meta-data information.
> This is the only officially supported tagging mechanism in FLAC. There may be only one VORBIS_COMMENT block in a stream.

> As such, when you state, that meta data is the domain of the encoder; this seems to ignore this fact, that there is no FLAC encoder support for mid-stream title updates.
> This is pretty much the same as for OGG and OPUS!
> As such, please point me to the encoder option you are referring to - as you seem to have implemented mid-stream meta-data updates from a FLAC stream, which doesn't exist in the FLAC specs?!


It's all the in specs. In the Ogg specs. See e.g. the overview page
here:
https://xiph.org/ogg/doc/oggstream.html

For Matroska based see:
https://www.matroska.org/technical/specs/index.html
and
https://www.matroska.org/technical/streaming/index.html



> However, for OGG you (ICEcast) implemented meta-data updates via the admin interface.

If you mean "Ogg" by "OGG" and "Icecast" by "ICEcast": No.
If you mean "Ogg/Vorbis" by "OGG": Long ago someone made a mistake and
actually implemented it. It is broken, it us unhelpful, and it even is a
security problem. And most importantly: it is against the specs. Just
don't use it. It's a bug based on a design flaw by Nullsoft to
workaround a design flaw of MP3.


> So why isn't this supported for OPUS and FLAC - as all three formats do use VORBIS_COMMENT and none of the encoders seems to support mid-stream meta-data updates.

Because we WILL NOT re-implement 30 year old bugs on new code.


> I am sorry, but I found the answers provided not really suited to my questions.
> 
> So any further help is appreciated.
> However, I will also ask the same question to the FLAC and OPUS mailing list.

See the link above.


> Thanks,
> Bernd
> 
> -----Ursprüngliche Nachricht-----
> Von: Philipp Schafft <phschafft at de.loewenfelsen.net> 
> Gesendet: Dienstag, 13. August 2019 14:09
> An: bn at radio42.com
> Cc: icecast-dev at xiph.org
> Betreff: Re: [Icecast-dev] MetaData Update for FLAC and OPUS
> 
> Good afternoon,
> 
> 
> 
> On Tue, 2019-08-13 at 13:36 +0200, bn at radio42.com wrote:
> > It seems, that with FLAC and OPUS streams (not individual files) the song title (meta data) updates do not work.
> > 
> > Also the ICEcast admin web interface isn’t working for FLAC and OPUS; while it is working for MP3, AAC as well as OGG streams.
> > 
> >  
> > 
> > I.e. when sending a continuous FLAC or OPUS stream to an ICEcast server, it seems impossible to update the meta data mid-stream (like it works for MP3, AAC or OGG).
> > 
> > I also couldn’t find any way to tell the original FLAC or OPUS encoder to perform the meta data update mid-stream.
> 
> Then that is a limitation of the encoder. You should contact the vendor of your encoder and ask them about it.
> 
> 
> 
> > Any suggestions?
> 
> See my reply here:
> http://lists.xiph.org/pipermail/icecast/2019-August/014767.html
> 
> 
> > Or are mid-stream meta-data updates simply not supported?
> 
> They are. And support is complete beside that they do not show up on the status page for FLAC based streams. But they are passed to the listener correctly.
> 
> 
> > If they support, I would be glad about any info on how to implement them.
> 
> You must tell your encoder to update the metadata. It's the encoder's job to send them.
> 
> 
> > If they are not supported, are there any plans to implement the admin meta data update interface also for FLAC and OPUS?
> 
> No. As metadata updates are already supported according to all relevant standards. Anything else would be outside the standards and would likely be more harm than good.


-- 
Philipp Schafft (CEO/Geschäftsführer) 
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