[Ffmpeg-devel] ReplayGain for Vorbis decoder

Måns Rullgård mru
Thu May 19 13:31:27 CEST 2005

Milan Cutka <milan_cutka at yahoo.com> writes:

>> castet.matthieu at free.fr writes:
>>> Selon Milan Cutka <milan_cutka at yahoo.com>:
>>>> I'm adding VorbisGain tag support to Vorbis decoder. It requires
>>>> parsing of comments header which I implemented already. Right now
>>>> I'm deciding whether to directly multiply decoded samples in
>>>> vorbis_decode_frame or add new field to AVCodecContext, fill it
>>>> with found multiplier and let the application to perform the
>>>> multiplication. I'd like to know your opinions. Thanks.
>>> Well it is quite ugly to pass option to vorbis decoder via comment
>>> which are normaly decoded in ogg demuxer...
>> I agree.  A better idea might be to have the demuxer fill in some
>> field in an appropriate place, and let the application deal with it.
>> ID3v2 tags can have similar things in them, if we'll ever support
>> those.
> When using libavcodec vorbis decoder in ffdshow I have to parse
> comment on my own, because I don't get information such as
> replaygain from demuxer. Of course I could parse the headers in my
> application and don't put it to libavcodec, but I guess it could be
> useful for other applications using libavcodec but not
> libavformat. And in my opinion replaygain is different from other
> comments like author, song name,... because it directly affects
> playback.

It's still only hint, right?  I don't think it's nice behavior of
decoders to do optional things that haven't been asked for.  If you
want to reencode the file with some other codec, doing things like
that might interfere and degrade the quality more than is necessary.

M?ns Rullg?rd
mru at inprovide.com

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