[opus] [PATCH] Support for Channel Mapping 253.
Jean-Marc Valin
jmvalin at jmvalin.ca
Thu Nov 2 16:54:31 UTC 2017
Hi Drew,
We're getting there... Some minor comments:
1) The public header file should not have an
#ifdef ENABLE_EXPERIMENTAL_AMBISONICS
since that would require the user code to define it.
2) Why do you have #define MAPPING_MATRIX_C ?
3) Looks like MAPPING_MATRIX_MAX_SIZE is not longer useful, right?
4) Even though it's not strictly necessary here, please add parentheses
to the definition of MATRIX_INDEX() to avoid nasty surprises in the
future (e.g. MATRIX_INDEX(...)*sizeof(foo) would be really bad).
Cheers,
Jean-Marc
On 10/31/2017 04:10 PM, Drew Allen wrote:
> Hi Jean-Marc,
>
> Thanks so much for your review. Attached are my comments and an updated
> patch.
>
> On Mon, Oct 30, 2017 at 5:48 PM Jean-Marc Valin <jmvalin at jmvalin.ca
> <mailto:jmvalin at jmvalin.ca>> wrote:
>
> Hi Drew,
>
> I've had some time to dig more deeply into your patch. Here's some more
> in-depth comments:
>
> 1) I note that your OpusMSEncoder struct in private.h adds a
> subframe_mem[] that's not in opus_multistream_encoder.c. I assume it's
> due to a merge problem (that field was removed some time ago), but can
> you confirm/fix the issue?
>
> Done. Yes, this is a merge conflict.
>
>
> 2) I noticed your patch adds many OPUS_EXPORT declarations. OPUS_EXPORT
> is only meant for functions exposed to the API (and in the include/
> directory), but I see several of these in mapping_matrix.h, which I
> think is incorrect.
>
> Done.
>
>
> 3) opus_projection_ambisonics_encoder_init() (which should be
> OPUS_EXPORT) is missing from opus_projection.h
>
> Done.
>
>
> 4) I believe mapping_matrix_get_size() should be returning
> align(sizeof(MappingMatrix)) + rows * cols * sizeof(opus_int16)
> rather than:
> align(sizeof(MappingMatrix) + rows * cols * sizeof(opus_int16))
> to match what mapping_matrix_get_data() does
>
> Done.
>
>
> 5) I'm not sure I understand the purpose of mapping_matrix_validate().
> Can the user really cause the matrix not to be valid? If yes, then can't
> this cause problems even earlier in the code? If not, then maybe an
> assertion would be better. Also, is the size of the matrix the only
> thing you can validate?
>
> Removed it. You're right, it's functionally impossible for the user to
> create an invalid matrix with the current API.
>
>
> 6) mapping_matrix_init() returns an error code, but the code that's
> calling it never checks it. Considering that it's an internal call, I
> would say it's probably better not to return anything, but instead to
> assert in the function.
>
> Done.
>
>
> 7) Same for mapping_matrix_multiply_short() and
> mapping_matrix_multiply_float(), the return value isn't checked. So it
> should either be replaced by an asssert or (if the user can cause a
> failure) actually checked.
>
> Done.
>
> 8) I see there's a "gain" field in the matrix, but I can't see it used
> anywhere. Did I miss something?
>
> Gain should be pulled out by the user via
> a OPUS_PROJECTION_GET_DEMIXING_MATRIX_GAIN call and add it to the
> overall output gain. We assume the mixing matrix gain is always zero and
> that this only matters for the output gain from the demixing matrix.
>
>
> 9) In get_streams_from_channels(), I think it'd be simpler to just
> replace:
> *streams = channels / 2 + (channels % 2 == 1);
> with:
> *streams = (channels+1) / 2;
>
> Done.
>
>
> 10) In opus_projection_ambisonics_encoder_init(), you to see if streams
> and coupled_streams are NULL, but unless I missed something I don't
> think there's any valid case where you wouldn't want to get those
> values. If you don't have them, then you have no way of knowing what
> mapping the encoder used, so no way of decoding. Instead, I would just
> return OPUS_BAD_ARG if they're NULL.
>
> Done.
>
>
> 11) So one issue I just noticed is that opus_projection_encode() and
> opus_projection_encode_float() (same for the decoder) use arbitrarily
> large amounts of stack memory for "buf". In opus_multistream_encode()
> that's avoided by converting just two channels at a time, but here it's
> not quite clear how to do that without duplicating a lot of the
> multistream code. If we can't address the issue with this patch, the
> least would be to abort when trying to use these calls with
> NONTHREADSAFE_PSEUDOSTACK
>
> Done. Let me know if we should try designing something around this.
>
>
> 12) I think opus_projection_decoder_ctl() is missing a va_end() call.
>
>
> Done.
>
>
>
> Cheers,
>
> Jean-Marc
>
>
>
> On 10/12/2017 05:44 PM, Drew Allen wrote:
> > thanks for all your feedback. here's the revised patch:
> >
> > On Wed, Oct 11, 2017 at 2:20 PM Timothy B. Terriberry
> <tterribe at xiph.org <mailto:tterribe at xiph.org>
> > <mailto:tterribe at xiph.org <mailto:tterribe at xiph.org>>> wrote:
> >
> > Jean-Marc Valin wrote:
> > > I think you'll want something like:
> > > (opus_int16)((unsigned)demixing_matrix[2*i+1] << 8)
> > > (though you might want to check it too)
> >
> > FWIW, we use the construct
> > int s = buf[2*i + 1] << 8 | buf[2*i];
> > s = ((s & 0xFFFF) ^ 0x8000) - 0x8000;
> >
> > to manually sign-extend the result in opus_compare (and also
> opus_demo).
> > If you ultimately cast s to (opus_int16), then I'm pretty sure
> most
> > compilers will turn the second line into a no-op and optimize
> it away.
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> <mailto:opus at xiph.org>>
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> >
> >
> >
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> >
>
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