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http://dev.sourcefabric.org/browse/LS-394?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14043#action_14043
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David Baelde commented on LS-394:
---------------------------------
I agree that there is no problem with libsamplerate_converter; as the previous
comment (by Romain in fact) says, the alloc in the name confused me.
Now, this ticket also mentionned a similar issue in Rutils.create_from_wav: in
that function, our code assumes that resampling can only drop data, whereas a
proper resampling would sometimes gives a little less, sometimes a little more.
This is fishy: we should clarify whether there is an issue or not.
> Resampling should be stateful
> -----------------------------
>
> Key: LS-394
> URL: http://dev.sourcefabric.org/browse/LS-394
> Project: Liquidsoap
> Issue Type: Bug
> Components: Liquidsoap
> Reporter: David Baelde
> Priority: Blocker
> Fix For: 1.0
>
>
> A close look at our resampled audio probably shows some glitches, because we
> create a new resampling object for each chunk:
> {{{
> Index: src/audio_converters/libsamplerate_converter.ml
> ===================================================================
> --- src/audio_converters/libsamplerate_converter.ml (revision 7444)
> +++ src/audio_converters/libsamplerate_converter.ml (working copy)
> @@ -56,6 +56,9 @@
> let samplerate_converter () =
> let quality = quality_of_string quality_conf#get in
> let converter = Samplerate.create quality 1 in
> + (* TODO seems to me that this code neglects the fact that libsamplerate's
> + * resampler has a state, missing the whole point of using a good
> resampler *)
> let convert ratio b ofs len =
> Samplerate.process_alloc converter ratio b ofs len
> in
> }}}
> There is also a similar problem in Rutils (see comment at the end of the
> file).
> I'd suggest to change not only liquidsoap modules but also the ocaml-resample
> API: libsamplerate has a type called state which became "type t" in OCaml...
> that probably participated in the confusion.
> By the way, libsamplerate and ocaml-samplerate have a simpler stateless API
> (http://www.mega-nerd.com/SRC/api.html), which we might as well use if we
> don't want to deal with states.
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