Commit 63396f39 authored by Jean-Marc Valin's avatar Jean-Marc Valin
Browse files

ietf doc: misc

parent 84966954
......@@ -243,9 +243,15 @@ bands is computed in compute_pbands() (<xref target="modes.c">modes.c</xref>).
<section anchor="CELT Encoder" title="CELT Encoder">
<!--Insert encoder overview-->
<t>
The basic block diagram of the CELT encoder is illustrated in <xref target="encoder-diagram"></xref>.
The encoder contains most of the building blocks of the decoder and can,
with very little extra computation, compute the signal that would be decoded by the decoder.
The top-level function for encoding a CELT frame in the reference implementation is
celt_encode() (<xref target="celt.c">celt.c</xref>).
</t>
<figure>
<figure anchor="encoder-diagram">
<artwork>
<![CDATA[
+-----------+ +--+
......@@ -274,13 +280,9 @@ bands is computed in compute_pbands() (<xref target="modes.c">modes.c</xref>).
+--------------------------------------+--------------------+
]]>
</artwork>
<postamble>Overview of the CELT encoder</postamble>
<postamble>Block diagram of the CELT encoder</postamble>
</figure>
<t>The top-level function for encoding a CELT frame in the reference implementation is
celt_encode() (<xref target="celt.c">celt.c</xref>).
</t>
<!--
<texttable anchor="bitstream">
<ttcol align='center'>Parameter(s)</ttcol>
......@@ -322,7 +324,7 @@ on the non-pre-emphasised signal. The inverse of the pre-emphasis is applied at
</section> <!-- pre-emphasis -->
<section anchor="range-coder" title="Range Coder">
<section anchor="range-encoder" title="Range Coder">
<t>
CELT uses an entropy coder based upon <xref target="range-coding"></xref>,
which is itself a rediscovery of the FIFO arithmetic code introduced by <xref target="coding-thesis"></xref>.
......@@ -335,7 +337,7 @@ larger bases (i.e.: a byte).
The range coder also acts as the bit-packer for CELT. It is
used in three different ways to encode:
<list style="symbols">
<t>symbols with a probability model using ec_encode() (<xref target="rangedec.c">rangeenc.c</xref>)</t>
<t>entropy-coded symbols with a fixed probability model using ec_encode() (<xref target="rangedec.c">rangeenc.c</xref>)</t>
<t>integers from 0 to 2^M-1 using ec_enc_uint() or ec_enc_bits() (<xref target="entenc.c">encenc.c</xref>)</t>
<t>integers from 0 to N-1 (where N is not a power of two) using ec_enc_uint() (<xref target="entenc.c">encenc.c</xref>)</t>
</list>
......@@ -650,10 +652,11 @@ Each CELT frame can be encoded in a different number of octets, making it possib
<section anchor="CELT-decoder" title="CELT Decoder">
<t>
Like for most audio codecs, the CELT decoder is less complex than the encoder.
Like for most audio codecs, the CELT decoder is less complex than the encoder, as can be
observed in the decoder block diagram in <xref target="decoder-diagram"></xref>.
</t>
<figure>
<figure anchor="decoder-diagram">
<artwork>
<![CDATA[
+--+
......@@ -679,7 +682,7 @@ Like for most audio codecs, the CELT decoder is less complex than the encoder.
+--------------------+
]]>
</artwork>
<postamble>Overview of the CELT decoder</postamble>
<postamble>Block diagram of the CELT decoder</postamble>
</figure>
<t>
......@@ -692,7 +695,8 @@ to the application that a problem has occured.
<section anchor="range-decoder" title="Range Decoder">
<t>
derf?
The range decoder extracts the symbols and integers encoded using the range encoder
<xref target="range-encoder"></xref>.
</t>
</section>
......@@ -706,17 +710,19 @@ derf?
<t>
The spherical codebook is decoded by alg_unquant() (<xref target="vq.c">vq.c</xref>).
The index of the PVQ entry is obtained from the range coder and converted to
a pulse vector by decode_pulses() (<xref target="cwrs.c">cwrs.c</xref>). Derf??
a pulse vector by decode_pulses() (<xref target="cwrs.c">cwrs.c</xref>).
</t>
<t>The decoded normalised vector for each band is equal to</t>
<t>X' = P + g_f * y,</t>
<t>where g_f = ( sqrt( (y^T*P)^2 + ||y||^2*(1-||P||^2) ) - y^T*P ) / ||y||^2. </t>
<t>
mix_pitch_and_residual() (<xref target="vq.c">vq.c</xref>).
This operation is implemented in mix_pitch_and_residual() (<xref target="vq.c">vq.c</xref>),
which is the same function as used in the encoder.
</t>
</section>
<section anchor="index-decoding" title="Index Decoding">
</section>
<section anchor="denormalization" title="Denormalization">
<t>
Just like each band was normalised in the encoder, the last step of the decoder before
......
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