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SSML document structure and events

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The Speech Synthesis Markup Language (SSML) with input text determines the structure, content, and other characteristics of the text to speech output. For example, you can use SSML to define a paragraph, a sentence, a break or a pause, or silence. You can wrap text with event tags such as bookmark or viseme that can be processed later by your application.

Refer to the sections below for details about how to structure elements in the SSML document.

Note

In addition to Azure AI Speech neural (non HD) voices, you can also use Azure AI Speech high definition (HD) voices and Azure OpenAI neural (HD and non HD) voices. The HD voices provide a higher quality for more versatile scenarios.

Some voices don't support all Speech Synthesis Markup Language (SSML) tags. This includes neural text to speech HD voices, personal voices, and embedded voices.

  • For Azure AI Speech high definition (HD) voices, check the SSML support here.
  • For personal voice, you can find the SSML support here.
  • For embedded voices, check the SSML support here.

Document structure

The Speech service implementation of SSML is based on the World Wide Web Consortium's Speech Synthesis Markup Language Version 1.0. The elements supported by the Speech can differ from the W3C standard.

Each SSML document is created with SSML elements or tags. These elements are used to adjust the voice, style, pitch, prosody, volume, and more.

Here's a subset of the basic structure and syntax of an SSML document:

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xmlns:mstts="https://www.w3.org/2001/mstts" xml:lang="string">
    <mstts:backgroundaudio src="string" volume="string" fadein="string" fadeout="string"/>
    <voice name="string" effect="string">
        <audio src="string"></audio>
        <bookmark mark="string"/>
        <break strength="string" time="string" />
        <emphasis level="value"></emphasis>
        <lang xml:lang="string"></lang>
        <lexicon uri="string"/>
        <math xmlns="http://www.w3.org/1998/Math/MathML"></math>
        <mstts:audioduration value="string"/>
        <mstts:ttsembedding speakerProfileId="string"></mstts:ttsembedding>
        <mstts:express-as style="string" styledegree="value" role="string"></mstts:express-as>
        <mstts:silence type="string" value="string"/>
        <mstts:viseme type="string"/>
        <p></p>
        <phoneme alphabet="string" ph="string"></phoneme>
        <prosody pitch="value" contour="value" range="value" rate="value" volume="value"></prosody>
        <s></s>
        <say-as interpret-as="string" format="string" detail="string"></say-as>
        <sub alias="string"></sub>
    </voice>
</speak>

Some examples of contents that are allowed in each element are described in the following list:

  • audio: The body of the audio element can contain plain text or SSML markup that's spoken if the audio file is unavailable or unplayable. The audio element can also contain text and the following elements: audio, break, p, s, phoneme, prosody, say-as, and sub.
  • bookmark: This element can't contain text or any other elements.
  • break: This element can't contain text or any other elements.
  • emphasis: This element can contain text and the following elements: audio, break, emphasis, lang, phoneme, prosody, say-as, and sub.
  • lang: This element can contain all other elements except mstts:backgroundaudio, voice, and speak.
  • lexicon: This element can't contain text or any other elements.
  • math: This element can only contain text and MathML elements.
  • mstts:audioduration: This element can't contain text or any other elements.
  • mstts:backgroundaudio: This element can't contain text or any other elements.
  • mstts:embedding: This element can contain text and the following elements: audio, break, emphasis, lang, phoneme, prosody, say-as, and sub.
  • mstts:express-as: This element can contain text and the following elements: audio, break, emphasis, lang, phoneme, prosody, say-as, and sub.
  • mstts:silence: This element can't contain text or any other elements.
  • mstts:viseme: This element can't contain text or any other elements.
  • p: This element can contain text and the following elements: audio, break, phoneme, prosody, say-as, sub, mstts:express-as, and s.
  • phoneme: This element can only contain text and no other elements.
  • prosody: This element can contain text and the following elements: audio, break, p, phoneme, prosody, say-as, sub, and s.
  • s: This element can contain text and the following elements: audio, break, phoneme, prosody, say-as, mstts:express-as, and sub.
  • say-as: This element can only contain text and no other elements.
  • sub: This element can only contain text and no other elements.
  • speak: The root element of an SSML document. This element can contain the following elements: mstts:backgroundaudio and voice.
  • voice: This element can contain all other elements except mstts:backgroundaudio and speak.

The Speech service automatically handles punctuation as appropriate, such as pausing after a period, or using the correct intonation when a sentence ends with a question mark.

Special characters

To use the characters &, <, and > within the SSML element's value or text, you must use the entity format. Specifically you must use &amp; in place of &, use &lt; in place of <, and use &gt; in place of >. Otherwise the SSML isn't parsed correctly.

For example, specify green &amp; yellow instead of green & yellow. The following SSML is parsed as expected:

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US">
    <voice name="en-US-AvaNeural">
        My favorite colors are green &amp; yellow.
    </voice>
</speak>

Special characters such as quotation marks, apostrophes, and brackets, must be escaped. For more information, see Extensible Markup Language (XML) 1.0: Appendix D.

Double or single quotation marks must enclose the attribute values. For example, <prosody volume="90"> and <prosody volume='90'> are well-formed, valid elements, but <prosody volume=90> isn't recognized.

Speak root element

The speak element contains information such as version, language, and the markup vocabulary definition. The speak element is the root element that's required for all SSML documents. You must specify the default language within the speak element, whether or not the language is adjusted elsewhere such as within the lang element.

Here's the syntax for the speak element:

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="string"></speak>
Attribute Description Required or optional
version Indicates the version of the SSML specification used to interpret the document markup. The current version is "1.0". Required
xml:lang The language of the root document. The value can contain a language code such as en (English), or a locale such as en-US (English - United States). Required
xmlns The URI to the document that defines the markup vocabulary (the element types and attribute names) of the SSML document. The current URI is "http://www.w3.org/2001/10/synthesis". Required

The speak element must contain at least one voice element.

speak examples

The supported values for attributes of the speak element were described previously.

Single voice example

This example uses the en-US-AvaNeural voice. For more examples, see voice examples.

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US">
    <voice name="en-US-AvaNeural">
        This is the text that is spoken.
    </voice>
</speak>

Add a break

Use the break element to override the default behavior of breaks or pauses between words. Otherwise the Speech service automatically inserts pauses.

Usage of the break element's attributes are described in the following table.

Attribute Description Required or optional
strength The relative duration of a pause by using one of the following values:
  • x-weak
  • weak
  • medium (default)
  • strong
  • x-strong
 Optional
time The absolute duration of a pause in seconds (such as 2s) or milliseconds (such as 500ms). Valid values range from 0 to 20000 milliseconds. If you set a value greater than the supported maximum, the service uses 20000ms. If the time attribute is set, the strength attribute is ignored. Optional

Here are more details about the strength attribute.

Strength Relative duration
X-weak 250 ms
Weak 500 ms
Medium 750 ms
Strong 1,000 ms
X-strong 1,250 ms

Break examples

The supported values for attributes of the break element were described previously. The following three ways all add 750 ms breaks.

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US">
    <voice name="en-US-AvaNeural">
        Welcome <break /> to text to speech.
        Welcome <break strength="medium" /> to text to speech.
        Welcome <break time="750ms" /> to text to speech.
    </voice>
</speak>

Add silence

Use the mstts:silence element to insert pauses before or after text, or between two adjacent sentences.

One of the differences between mstts:silence and break is that a break element can be inserted anywhere in the text. Silence only works at the beginning or end of input text or at the boundary of two adjacent sentences.

The silence setting is applied to all input text within its enclosing voice element. To reset or change the silence setting again, you must use a new voice element with either the same voice or a different voice.

Usage of the mstts:silence element's attributes are described in the following table.

Attribute Description Required or optional
type Specifies where and how to add silence. The following silence types are supported:
  • Leading – Extra silence at the beginning of the text. The value that you set is added to the natural silence before the start of text.
  • Leading-exact – Silence at the beginning of the text. The value is an absolute silence length.
  • Tailing – Extra silence at the end of text. The value that you set is added to the natural silence after the last word.
  • Tailing-exact – Silence at the end of the text. The value is an absolute silence length.
  • Sentenceboundary – Extra silence between adjacent sentences. The actual silence length for this type includes the natural silence after the last word in the previous sentence, the value you set for this type, and the natural silence before the starting word in the next sentence.
  • Sentenceboundary-exact – Silence between adjacent sentences. The value is an absolute silence length.
  • Comma-exact – Silence at the comma in half-width or full-width format. The value is an absolute silence length.
  • Semicolon-exact – Silence at the semicolon in half-width or full-width format. The value is an absolute silence length.
  • Enumerationcomma-exact – Silence at the enumeration comma in full-width format. The value is an absolute silence length.

An absolute silence type (with the -exact suffix) replaces any otherwise natural leading or trailing silence. Absolute silence types take precedence over the corresponding non-absolute type. For example, if you set both Leading and Leading-exact types, the Leading-exact type takes effect. The WordBoundary event takes precedence over punctuation-related silence settings including Comma-exact, Semicolon-exact, or Enumerationcomma-exact. When you use both the WordBoundary event and punctuation-related silence settings, the punctuation-related silence settings don't take effect.		 Required
Value The duration of a pause in seconds (such as 2s) or milliseconds (such as 500ms). Valid values range from 0 to 20000 milliseconds. If you set a value greater than the supported maximum, the service uses 20000ms. Required

mstts silence examples

The supported values for attributes of the mstts:silence element were described previously.

In this example, mstts:silence is used to add 200 ms of silence between two sentences.

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xmlns:mstts="http://www.w3.org/2001/mstts" xml:lang="en-US">
<voice name="en-US-AvaNeural">
<mstts:silence  type="Sentenceboundary" value="200ms"/>
If we're home schooling, the best we can do is roll with what each day brings and try to have fun along the way.
A good place to start is by trying out the slew of educational apps that are helping children stay happy and smash their schooling at the same time.
</voice>
</speak>

In this example, mstts:silence is used to add 50 ms of silence at the comma, 100 ms of silence at the semicolon, and 150 ms of silence at the enumeration comma.

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xmlns:mstts="http://www.w3.org/2001/mstts" xml:lang="zh-CN">
<voice name="zh-CN-YunxiNeural">
<mstts:silence type="comma-exact" value="50ms"/><mstts:silence type="semicolon-exact" value="100ms"/><mstts:silence type="enumerationcomma-exact" value="150ms"/>你好呀，云希、晓晓；你好呀。
</voice>
</speak>

Specify paragraphs and sentences

The p and s elements are used to denote paragraphs and sentences, respectively. In the absence of these elements, the Speech service automatically determines the structure of the SSML document.

Paragraph and sentence examples

The following example defines two paragraphs that each contain sentences. In the second paragraph, the Speech service automatically determines the sentence structure, since they aren't defined in the SSML document.

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US">
    <voice name="en-US-AvaNeural">
        <p>
            <s>Introducing the sentence element.</s>
            <s>Used to mark individual sentences.</s>
        </p>
        <p>
            Another simple paragraph.
            Sentence structure in this paragraph is not explicitly marked.
        </p>
    </voice>
</speak>

Bookmark element

You can use the bookmark element in SSML to reference a specific location in the text or tag sequence. Then you use the Speech SDK and subscribe to the BookmarkReached event to get the offset of each marker in the audio stream. The bookmark element isn't spoken. For more information, see Subscribe to synthesizer events.

Usage of the bookmark element's attributes are described in the following table.

Attribute Description Required or optional
mark The reference text of the bookmark element. Required

Bookmark examples

The supported values for attributes of the bookmark element were described previously.

As an example, you might want to know the time offset of each flower word in the following snippet:

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US">
    <voice name="en-US-AvaNeural">
        We are selling <bookmark mark='flower_1'/>roses and <bookmark mark='flower_2'/>daisies.
    </voice>
</speak>

Viseme element

A viseme is the visual description of a phoneme in spoken language. It defines the position of the face and mouth while a person is speaking. You can use the mstts:viseme element in SSML to request viseme output. For more information, see Get facial position with viseme.

The viseme setting is applied to all input text within its enclosing voice element. To reset or change the viseme setting again, you must use a new voice element with either the same voice or a different voice.

Usage of the viseme element's attributes are described in the following table.

Attribute Description Required or optional
type The type of viseme output.
  • redlips_front – lip-sync with viseme ID and audio offset output
  • FacialExpression – blend shapes output
 Required

Note

Currently, redlips_front only supports neural voices in en-US locale, and FacialExpression supports neural voices in en-US and zh-CN locales.

Viseme examples

The supported values for attributes of the viseme element were described previously.

This SSML snippet illustrates how to request blend shapes with your synthesized speech.

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xmlns:mstts="http://www.w3.org/2001/mstts" xml:lang="en-US">
  <voice name="en-US-AvaNeural">
    <mstts:viseme type="FacialExpression"/>
    Rainbow has seven colors: Red, orange, yellow, green, blue, indigo, and violet.
  </voice>
</speak>

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