Update to opus-HEAD-66611f1.

doc/draft-ietf-codec-opus-update.xml

 <?xml version="1.0" encoding="US-ASCII"?>
 <!DOCTYPE rfc SYSTEM "rfc2629.dtd">
 <?rfc toc="yes"?>
 <?rfc tocompact="yes"?>
 <?rfc tocdepth="3"?>
 <?rfc tocindent="yes"?>
 <?rfc symrefs="yes"?>
 <?rfc sortrefs="yes"?>
 <?rfc comments="yes"?>
 <?rfc inline="yes"?>
 <?rfc compact="yes"?>
 <?rfc subcompact="no"?>
-<rfc category="std" docName="draft-valin-codec-opus-update-00"
+<rfc category="std" docName="draft-ietf-codec-opus-update-01"
      ipr="trust200902">
   <front>
     <title abbrev="Opus Update">Updates to the Opus Audio Codec</title>
 
 <author initials="JM" surname="Valin" fullname="Jean-Marc Valin">
 <organization>Mozilla Corporation</organization>
 <address>
 <postal>
-<street>650 Castro Street</street>
+<street>331 E. Evelyn Avenue</street>
 <city>Mountain View</city>
 <region>CA</region>
 <code>94041</code>
 <country>USA</country>
 </postal>
 <phone>+1 650 903-0800</phone>
 <email>jmvalin@jmvalin.ca</email>
 </address>
 </author>
 
-<author initials="T." surname="Terriberry" fullname="Timothy B. Terriberry">
-<organization>Mozilla Corporation</organization>
-<address>
-<postal>
-<street>650 Castro Street</street>
-<city>Mountain View</city>
-<region>CA</region>
-<code>94041</code>
-<country>USA</country>
-</postal>
-<phone>+1 650 903-0800</phone>
-<email>tterriberry@mozilla.com</email>
-</address>
-</author>
-
 <author initials="K." surname="Vos" fullname="Koen Vos">
-<organization>Skype Technologies S.A.</organization>
+<organization>vocTone</organization>
 <address>
 <postal>
-<street>Soder Malarstrand 43</street>
-<city>Stockholm</city>
+<street></street>
+<city></city>
 <region></region>
-<code>11825</code>
-<country>SE</country>
+<code></code>
+<country></country>
 </postal>
-<phone>+46 73 085 7619</phone>
-<email>koen.vos@skype.net</email>
+<phone></phone>
+<email>koenvos74@gmail.com</email>
 </address>
 </author>
 
 
 
-    <date day="12" month="July" year="2013" />
+    <date day="4" month="September" year="2014" />
 
     <abstract>
       <t>This document addresses minor issues that were found in the specification
       of the Opus audio codec in <xref target="RFC6716">RFC 6716</xref>.</t>
     </abstract>
   </front>
 
   <middle>
     <section title="Introduction">
-      <t>This document address minor issues that were discovered in the reference
-      implementation of the Opus codec that serves as the specification in 
+      <t>This document addresses minor issues that were discovered in the reference
+      implementation of the Opus codec that serves as the specification in
       <xref target="RFC6716">RFC 6716</xref>. Only issues affecting the decoder are
       listed here. An up-to-date implementation of the Opus encoder can be found at
       http://opus-codec.org/. The updated specification remains fully compatible with
       the original specification and only one of the changes results in any difference
       in the audio output.
       </t>
     </section>
 
     <section title="Terminology">
       <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
       document are to be interpreted as described in <xref
       target="RFC2119">RFC 2119</xref>.</t>
     </section>
 
     <section title="Stereo State Reset in SILK">
       <t>The reference implementation does not reinitialize the stereo state
       during a mode switch. The old stereo memory can produce a brief impulse
       (i.e. single sample) in the decoded audio. This can be fixed by changing
       silk/dec_API.c at line 72:
       <figure>
       <artwork><![CDATA[
      for( n = 0; n < DECODER_NUM_CHANNELS; n++ ) {
          ret  = silk_init_decoder( &channel_state[ n ] );
      }
-+    silk_memset(&((silk_decoder *)decState)->sStereo, 0, 
++    silk_memset(&((silk_decoder *)decState)->sStereo, 0,
 +                sizeof(((silk_decoder *)decState)->sStereo));
 +    /* Not strictly needed, but it's cleaner that way */
 +    ((silk_decoder *)decState)->prev_decode_only_middle = 0;
  
      return ret;
  }
 ]]></artwork>
 </figure>
      This change affects the normative part of the decoder. Fortunately,
      the modified decoder is still compliant with the original specification because
@@ skipping 27 matching lines @@
 -         len -= padding;
        }
 ]]></artwork>
 </figure>
       </t>
       <t>This packet parsing issue is limited to reading memory up
          to about 60 kB beyond the compressed buffer. This can only be triggered
          by a compressed packet more than about 16 MB long, so it's not a problem
          for RTP. In theory, it <spanx style="emph">could</spanx> crash a file
          decoder (e.g. Opus in Ogg) if the memory just after the incoming packet
-         is out-of-range, but that could not be achieved when attempted in a production
-         application built using an affected version of the Opus decoder.</t>
+         is out-of-range, but our attempts to trigger such a crash in a production
+         application built using an affected version of the Opus decoder failed.</t>
     </section>
 
     <section anchor="resampler" title="Resampler buffer">
       <t>The SILK resampler had the following issues:
         <list style="numbers">
     <t>The calls to memcpy() were using sizeof(opus_int32), but the type of the
         local buffer was opus_int16.</t>
     <t>Because the size was wrong, this potentially allowed the source
-        and destination regions of the memcpy overlap.
+        and destination regions of the memcpy() to overlap.
           We <spanx style="emph">believe</spanx> that nSamplesIn is at least fs_in_khZ,
           which is at least 8.
-       Since RESAMPLER_ORDER_FIR_12 is only 8,that should not be a problem once
+       Since RESAMPLER_ORDER_FIR_12 is only 8, that should not be a problem once
        the type size is fixed.</t>
           <t>The size of the buffer used RESAMPLER_MAX_BATCH_SIZE_IN, but the
         data stored in it was actually _twice_ the input batch size
         (nSamplesIn&lt;&lt;1).</t>
       </list></t>
       <t>
       The fact that the code never produced any error in testing (including when run under the
       Valgrind memory debugger), suggests that in practice
      the batch sizes are reasonable enough that none of the issues above
      was ever a problem. However, proving that is non-obvious.
     </t>
-    <t>The code can be fixed by applying the following changes to like 70 of silk/resampler_private_IIR_FIR.c:
+    <t>The code can be fixed by applying the following changes to line 70 of silk/resampler_private_IIR_FIR.c:
 <figure>
 <artwork><![CDATA[
-     opus_int16                      out[],          /* O    Output signal               */
-     const opus_int16                in[],           /* I    Input signal                */
-     opus_int32                      inLen           /* I    Number of input samples     */
  )
  {
-     silk_resampler_state_struct *S = (silk_resampler_state_struct *)SS;
+     silk_resampler_state_struct *S = \
+(silk_resampler_state_struct *)SS;
      opus_int32 nSamplesIn;
      opus_int32 max_index_Q16, index_increment_Q16;
--    opus_int16 buf[ RESAMPLER_MAX_BATCH_SIZE_IN + RESAMPLER_ORDER_FIR_12 ];
-+    opus_int16 buf[ 2*RESAMPLER_MAX_BATCH_SIZE_IN + RESAMPLER_ORDER_FIR_12 ];
+-    opus_int16 buf[ RESAMPLER_MAX_BATCH_SIZE_IN + \
+RESAMPLER_ORDER_FIR_12 ];
++    opus_int16 buf[ 2*RESAMPLER_MAX_BATCH_SIZE_IN + \
+RESAMPLER_ORDER_FIR_12 ];
  
      /* Copy buffered samples to start of buffer */
--    silk_memcpy( buf, S->sFIR, RESAMPLER_ORDER_FIR_12 * sizeof( opus_int32 ) );
-+    silk_memcpy( buf, S->sFIR, RESAMPLER_ORDER_FIR_12 * sizeof( opus_int16 ) );
+-    silk_memcpy( buf, S->sFIR, RESAMPLER_ORDER_FIR_12 \
+* sizeof( opus_int32 ) );
++    silk_memcpy( buf, S->sFIR, RESAMPLER_ORDER_FIR_12 \
+* sizeof( opus_int16 ) );
  
      /* Iterate over blocks of frameSizeIn input samples */
      index_increment_Q16 = S->invRatio_Q16;
      while( 1 ) {
          nSamplesIn = silk_min( inLen, S->batchSize );
  
          /* Upsample 2x */
-         silk_resampler_private_up2_HQ( S->sIIR, &buf[ RESAMPLER_ORDER_FIR_12 ], in, nSamplesIn );
+         silk_resampler_private_up2_HQ( S->sIIR, &buf[ \
+RESAMPLER_ORDER_FIR_12 ], in, nSamplesIn );
  
-         max_index_Q16 = silk_LSHIFT32( nSamplesIn, 16 + 1 );         /* + 1 because 2x upsampling */
-         out = silk_resampler_private_IIR_FIR_INTERPOL( out, buf, max_index_Q16, index_increment_Q16 );
+         max_index_Q16 = silk_LSHIFT32( nSamplesIn, 16 + 1 \
+);         /* + 1 because 2x upsampling */
+         out = silk_resampler_private_IIR_FIR_INTERPOL( out, \
+buf, max_index_Q16, index_increment_Q16 );
          in += nSamplesIn;
          inLen -= nSamplesIn;
  
          if( inLen > 0 ) {
-             /* More iterations to do; copy last part of filtered signal to beginning of buffer */
--            silk_memcpy( buf, &buf[ nSamplesIn << 1 ], RESAMPLER_ORDER_FIR_12 * sizeof( opus_int32 ) );
-+            silk_memmove( buf, &buf[ nSamplesIn << 1 ], RESAMPLER_ORDER_FIR_12 * sizeof( opus_int16 ) );
+             /* More iterations to do; copy last part of \
+filtered signal to beginning of buffer */
+-            silk_memcpy( buf, &buf[ nSamplesIn << 1 ], \
+RESAMPLER_ORDER_FIR_12 * sizeof( opus_int32 ) );
++            silk_memmove( buf, &buf[ nSamplesIn << 1 ], \
+RESAMPLER_ORDER_FIR_12 * sizeof( opus_int16 ) );
          } else {
              break;
          }
      }
  
-     /* Copy last part of filtered signal to the state for the next call */
--    silk_memcpy( S->sFIR, &buf[ nSamplesIn << 1 ], RESAMPLER_ORDER_FIR_12 * sizeof( opus_int32 ) );
-+    silk_memcpy( S->sFIR, &buf[ nSamplesIn << 1 ], RESAMPLER_ORDER_FIR_12 * sizeof( opus_int16 ) );
+     /* Copy last part of filtered signal to the state for \
+the next call */
+-    silk_memcpy( S->sFIR, &buf[ nSamplesIn << 1 ], \
+RESAMPLER_ORDER_FIR_12 * sizeof( opus_int32 ) );
++    silk_memcpy( S->sFIR, &buf[ nSamplesIn << 1 ], \
+RESAMPLER_ORDER_FIR_12 * sizeof( opus_int16 ) );
  }
 ]]></artwork>
 </figure>
+    Note: due to RFC formatting conventions, lines exceeding the column width
+    in the patch above are split using a backslash character. The backslashes
+    at the end of a line and the white space at the beginning
+    of the following line are not part of the patch. A properly formatted patch
+    including the three changes above is available at
+    <eref target="http://jmvalin.ca/misc_stuff/opus_update.patch"/>.
     </t>
     </section>
-    
+
     <section title="Downmix to Mono">
       <t>The last issue is not strictly a bug, but it is an issue that has been reported
-      when downmixing Opus decoded stream to mono, whether this is done inside the decoder
-      or as a post-processing on the stereo decoder output. Opus intensity stereo allows
-      optionally coding the two channels 180-degrees out of phase on a per-band basis. 
+      when downmixing an Opus decoded stream to mono, whether this is done inside the decoder
+      or as a post-processing step on the stereo decoder output. Opus intensity stereo allows
+      optionally coding the two channels 180-degrees out of phase on a per-band basis.
       This provides better stereo quality than forcing the two channels to be in phase,
       but when the output is downmixed to mono, the energy in the affected bands is cancelled
       sometimes resulting in audible artefacts.
       </t>
-      <t>A possible work-around for this issue would be to optionally allow the decoder to
-      not apply the 180-degree phase shift when the output is meant to be downmixed (inside or
+      <t>As a work-around for this issue, the decoder MAY choose not to apply the 180-degree
+      phase shift when the output is meant to be downmixed (inside or
       outside of the decoder).
       </t>
     </section>
     <section anchor="IANA" title="IANA Considerations">
       <t>This document makes no request of IANA.</t>
 
       <t>Note to RFC Editor: this section may be removed on publication as an
       RFC.</t>
     </section>
 
     <section anchor="Acknowledgements" title="Acknowledgements">
       <t>We would like to thank Juri Aedla for reporting the issue with the parsing of
       the Opus padding.</t>
     </section>
   </middle>
 
   <back>
     <references title="References">
       <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?>
       <?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.6716.xml"?>
 
 
     </references>
   </back>
 </rfc>