[Vorbis-dev] libvorbis 1.2.2 RC1 -- comment padding

[Michael Gold]

On Tue, Dec 16, 2008 at 21:40:46 +0100, ogg.k.ogg.k at googlemail.com wrote:
> > Pasting a block of lyrics into a file could add around 2K. Padding to 4K
> > doesn't seem unreasonable, especially considering most Vorbis files will
> > be several megabytes. Are there cases where the size would be a problem?
> 
> Streaming: headers are burst sent to the listener. Still might not be
> that significant.

Are files generally re-encoded for streaming? If so, an encoder option to
disable padding should be sufficient. Another option would be to modify
the stream server to strip comment padding.

> > I suppose adding lyrics isn't really an operation suited to mass tagging,
> > so 256 bytes might be reasonable for most cases. However, even rewriting
> > a single file is annoying if that file is large (e.g., it it's a movie).
> 
> FWIW, ffmpeg2theora stores its comments primarily on the video
> stream (other encoders might differ though), so this patch would
> have no effect on movies encoded with ffmpeg2theora.

My test file was muxed using ogmmerge. This isn't a Xiph.org tool but it
can associate tags like LANGUAGE with each audio stream. If such tags
are also used in Theora files, padding would be useful (and the relative
filesize probably makes it less of a concern).

Presumably we'd also want similar padding on the non-Vorbis streams in
the future.

> > Maybe the amount of padding should be based on the filesize somehow,
> > with no padding for very small files.
> 
> Sounds sensible for the default value.

Though this logic probably doesn't belong in libvorbis, and the encoder
would need to pick arbitrarily when encoding from stdin.

-- Michael
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