[LAD] [Ann] Folve: Fuse file system that convolves flac files on-the-fly

Paul Giblock pgiblox at gmail.com
Tue Sep 18 00:16:17 UTC 2012

On Sep 17, 2012 8:04 PM, "Henner Zeller" <h.zeller at acm.org> wrote:
> Hi,
> On 16 September 2012 09:10, Fons Adriaensen <fons at linuxaudio.org> wrote:
>> On Sun, Sep 16, 2012 at 12:46:42AM -0700, Henner Zeller wrote:
>> > Over the week or so, I've build some fuse filesystem filters flac files
>> > on-the-fly
>> > using the zita convolver. This makes it real easy to play
>> > around with files and filters. In particular with systems that
>> > don't support stream convolving, but just can read files.
>> Interesting project...
>> One thing: when skipping forward (or seeking in general)
>> there's no need to convolve all data up to that point.
>> If P is the new position and L is the lenght of the IR,
>> then just call Convproc->reset(), seek the input file to
>> P - L (or 0 if P < L), and convolve up to P. You're
>> computing a FIR filter, so no more history is required.
> I know. The only reason for doing what I am doing is entirely because of
the filesystem semantics.
> On the filesystem level, I don't 'see' seeks to audio frame positions but
_only_ file positions. Since the input and the output is a compressed flac
file, the relationship cannot be predicted - this is why I have to walk up
to that point to present a consistent view of the file (in particular if
that file is mmap()ed or if users jump around in it, this is important).
> (this would be different if input and output was wav where the
relationship is clear; but wav doesn't provide such a rich header format,
so that the user in media server that display tags and images would be bad).
>> If the seek involves an output discontinuity for the user,
>> you could even just call Conproc->reset(), seek to P, and
>> proceed normally. The result will be as if there was only
>> silence before P.
>> Ciao,
>> --
>> FA
>> A world of exhaustive, reliable metadata would be an utopia.
>> It's also a pipe-dream, founded on self-delusion, nerd hubris
>> and hysterically inflated market opportunities. (Cory Doctorow)
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Have you considered OggPCM? Perhaps it has a constant enough bitrate while
still providing rich tags. Not sure how well supported it is though...
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