ref: d481798ad1f3fc6a51630acae10eff032b681142
parent: 602fd8a6f8228189ce78eb14d8b3a0d6b4f5a6e7
author: Jean-Marc Valin <[email protected]>
date: Wed Oct 26 11:47:53 EDT 2011
draft: Update to normative/non-normative switching Making SILK bandwidth changes non-normative when there's no redundancy
--- a/doc/draft-ietf-codec-opus.xml
+++ b/doc/draft-ietf-codec-opus.xml
@@ -5433,7 +5433,10 @@
nor the LTP, LPC, stereo unmixing, and resampler buffers are available at the
new sample rate.
These switches SHOULD be delayed by the encoder until quiet periods or
- transients, where the inevitable glitches will be less audible.
+ transients, where the inevitable glitches will be less audible. Additionally,
+ the bit-stream MAY include redundant side information ("redundancy"), in the + form of additional CELT frames embedded in each of the Opus frames around the
+ transition.
</t>
<t>
@@ -5453,17 +5456,14 @@
<t>
A transition between coding the lower frequencies with the LP model and the
- MDCT model is only normatively specified when it includes redundancy.
+ MDCT model or a transition that involves changing the SILK bandwidth
+ is only normatively specified when it includes redundancy.
For those without redundancy, it is RECOMMENDED that the decoder use a
concealment technique (e.g., make use of a PLC algorithm) to "fill in" the
gap or discontinuity caused by the mode transition.
-Transitions between SILK-only modes without redundancy are normative, however,
- as these often occur at bitrates that are too low to reasonably include the
- extra side information.
-Therefore, PLC MUST NOT be applied during a transition when
+Therefore, PLC MUST NOT be applied during any normative transition, i.e., when
<list style="symbols">
<t>A packet includes redundancy for this transition (as described below),</t>
-<t>The transition is between two SILK-mode packets,</t>
<t>The transition is between any WB SILK packet and any Hybrid packet, or vice
versa,</t>
<t>The transition is between any two Hybrid mode packets, or</t>
@@ -5661,14 +5661,10 @@
<figure align="center" anchor="normative_transitions"
title="Normative Transitions">
<artwork align="center"><![CDATA[
-SILK to SILK (audio bandwidth change): S -> S -> S ;S -> S -> S
-
SILK to SILK with Redundancy: S -> S -> S ;S -> S -> S
& &
!R -> R
-NB or MB SILK to Hybrid: S -> S -> S |H -> H -> H
-
NB or MB SILK to Hybrid with Redundancy: S -> S -> S
&
!R ->;H -> H -> H
@@ -5679,14 +5675,10 @@
&
!R -> C -> C -> C
-Hybrid to NB or MB SILK: H -> H -> H -> c
- +
- ;S -> S -> S
+Hybrid to NB or MB SILK with Redundancy: H -> H -> H ;S -> S -> S
+ & &
+ !R -> R
-Hybrid to NB or MB SILK with Redundancy: H -> H -> H -> R
- &
- ;S -> S -> S
-
Hybrid to WB SILK: H -> H -> H -> c
\ +
> S -> S -> S
@@ -5717,8 +5709,7 @@
</t>
<t>
-For transitions without redundancy, the use of PLC (as RECOMMENDED above) means
- their behavior is non-normative.
+The behavior of transitions without redundancy where PLC is allowed is non-normative.
An encoder might still wish to use these transitions if, for example, it
doesn't want to add the extra bitrate required for redundancy or if it makes
a decision to switch after it has already transmitted the frame that would
@@ -5728,9 +5719,17 @@
<figure align="center" anchor="nonnormative_transitions"
title="Recommended Non-Normative Transitions">
<artwork align="center"><![CDATA[
+SILK to SILK (audio bandwidth change): S -> S -> S ;S -> S -> S
+
+NB or MB SILK to Hybrid: S -> S -> S |H -> H -> H
+
SILK to CELT without Redundancy: S -> S -> S -> P
&
!C -> C -> C
+
+Hybrid to NB or MB SILK: H -> H -> H -> c
+ +
+ ;S -> S -> S
Hybrid to CELT without Redundancy: H -> H -> H -> P
&