SSML (Dialogflow)

When returning a response to Google Assistant, you can use a subset of the Speech Synthesis Markup Language (SSML) in your responses. By using SSML, you can make your conversation's responses seem more like natural speech. The following shows an example of SSML markup and how it's read back by Google Assistant.

function saySSML(conv) {
  const ssml = '<speak>' +
    'Here are <say-as interpret-as="characters">SSML</say-as> samples. ' +
    'I can pause <break time="3" />. ' +
    'I can play a sound <audio src="https://www.example.com/MY_WAVE_FILE.wav">your wave file</audio>. ' +
    'I can speak in cardinals. Your position is <say-as interpret-as="cardinal">10</say-as> in line. ' +
    'Or I can speak in ordinals. You are <say-as interpret-as="ordinal">10</say-as> in line. ' +
    'Or I can even speak in digits. Your position in line is <say-as interpret-as="digits">10</say-as>. ' +
    'I can also substitute phrases, like the <sub alias="World Wide Web Consortium">W3C</sub>. ' +
    'Finally, I can speak a paragraph with two sentences. ' +
    '<p><s>This is sentence one.</s><s>This is sentence two.</s></p>' +
    '</speak>';
  conv.ask(ssml);
}

{
  "expectUserResponse": true,
  "expectedInputs": [
    {
      "possibleIntents": [
        {
          "intent": "actions.intent.TEXT"
        }
      ],
      "inputPrompt": {
        "richInitialPrompt": {
          "items": [
            {
              "simpleResponse": {
                "textToSpeech": "<speak>Here are <say-as interpret-as=\"characters\">SSML</say-as> samples. I can pause <break time=\"3\" />. I can play a sound <audio src=\"https://www.example.com/MY_WAVE_FILE.wav\">your wave file</audio>. I can speak in cardinals. Your position is <say-as interpret-as=\"cardinal\">10</say-as> in line. Or I can speak in ordinals. You are <say-as interpret-as=\"ordinal\">10</say-as> in line. Or I can even speak in digits. Your position in line is <say-as interpret-as=\"digits\">10</say-as>. I can also substitute phrases, like the <sub alias=\"World Wide Web Consortium\">W3C</sub>. Finally, I can speak a paragraph with two sentences. <p><s>This is sentence one.</s><s>This is sentence two.</s></p></speak>"
              }
            }
          ]
        }
      }
    }
  ]
}

Audio

SSML is supported in the Actions simulator, but not the Dialogflow simulator.

URLs in SSML

When defining an SSML response that only includes a URL, ampersands in that URL can cause issues due to XML formatting. To ensure the URL is properly referenced, replace instances of & with &.

Even if your SSML response only includes a URL, Actions on Google requires display text for the response. Because text inside the <audio> tag won't be spoken by Assistant, you can insert filler text or a short description in your <audio> tag to meet this requirement. Text inside the <audio> tag won't be spoken by Assistant after the audio plays, and meets Action on Google's requirement for a display text version of your SSML.

Here's an example of a problematic SSML response:

<speak>
  <audio src="https://firebasestorage.googleapis.com/v0/b/project-name.appspot.com/o/audio-file-name.ogg?alt=media&token=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX">
  </audio>
</speak>

The above example doesn't escape the & for proper XML formatting.

A fixed version of the same SSML response looks like this:

<speak>
  <audio src="https://firebasestorage.googleapis.com/v0/b/project-name.appspot.com/o/audio-file-name.ogg?alt=media&amp;token=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX">
  text
  </audio>
</speak>

Support for SSML elements

The following sections describe the SSML elements and options that can be used in your Actions.

<speak>

The root element of the SSML response.

To learn more about the speak element, see the W3 specification.

Example

<speak>
  my SSML content
</speak>

<break>

An empty element that controls pausing or other prosodic boundaries between words. Using <break> between any pair of tokens is optional. If this element is not present between words, the break is automatically determined based on the linguistic context.

To learn more about the break element, see the W3 specification.

Attributes

Example

The following example shows how to use the <break> element to pause between steps:

<speak>
  Step 1, take a deep breath. <break time="200ms"/>
  Step 2, exhale.
  Step 3, take a deep breath again. <break strength="weak"/>
  Step 4, exhale.
</speak>

<say‑as>

This element lets you indicate information about the type of text construct that is contained within the element. It also helps specify the level of detail for rendering the contained text.

The <say‑as> element has the required attribute, interpret-as, which determines how the value is spoken. Optional attributes format and detail may be used depending on the particular interpret-as value.

Examples

The interpret-as attribute supports the following values:

• currency

  The following example is spoken as "forty two dollars and one cent". If the language attribute is omitted, it uses the current locale.

  <speak>
    <say-as interpret-as='currency' language='en-US'>$42.01</say-as>
  </speak>
      

• telephone

  See the interpret-as='telephone' description in the W3C SSML 1.0 say-as attribute values WG note.

  The following example is spoken as "one eight zero zero two zero two one two one two". If the "google:style" attribute is omitted, it speaks zero as letter O.

  The "google:style='zero-as-zero'" attribute currently only works in EN locales.

        <speak>
          <say-as interpret-as='telephone' google:style='zero-as-zero'>1800-202-1212</say-as>
        </speak>
      

• verbatim or spell-out

  The following example is spelled out letter by letter:

  <speak>
    <say-as interpret-as="verbatim">abcdefg</say-as>
  </speak>
      

• date

  The format attribute is a sequence of date field character codes. Supported field character codes in format are {y, m, d} for year, month, and day (of the month) respectively. If the field code appears once for year, month, or day then the number of digits expected are 4, 2, and 2 respectively. If the field code is repeated then the number of expected digits is the number of times the code is repeated. Fields in the date text may be separated by punctuation and/or spaces.

  The detail attribute controls the spoken form of the date. For detail='1' only the day fields and one of month or year fields are required, although both may be supplied. This is the default when less than all three fields are given. The spoken form is "The {ordinal day} of {month}, {year}".

  The following example is spoken as "The tenth of September, nineteen sixty":

  <speak>
    <say-as interpret-as="date" format="yyyymmdd" detail="1">
      1960-09-10
    </say-as>
  </speak>
      

  The following example is spoken as "The tenth of September":

  <speak>
    <say-as interpret-as="date" format="dm">10-9</say-as>
  </speak>
      

  For detail='2' the day, month, and year fields are required and this is the default when all three fields are supplied. The spoken form is "{month} {ordinal day}, {year}".

  The following example is spoken as "September tenth, nineteen sixty":

  <speak>
    <say-as interpret-as="date" format="dmy" detail="2">
      10-9-1960
    </say-as>
  </speak>
      

• characters

  The following example is spoken as "C A N":

  <speak>
    <say-as interpret-as="characters">can</say-as>
  </speak>
      

• cardinal

  The following example is spoken as "Twelve thousand three hundred forty five" (for US English) or "Twelve thousand three hundred and forty five (for UK English)":

  <speak>
    <say-as interpret-as="cardinal">12345</say-as>
  </speak>
      

• ordinal

  The following example is spoken as "First":

  <speak>
    <say-as interpret-as="ordinal">1</say-as>
  </speak>
      

• fraction

  The following example is spoken as "five and a half":

  <speak>
    <say-as interpret-as="fraction">5+1/2</say-as>
  </speak>
      

• expletive or bleep

  The following example comes out as a beep, as though it has been censored:

  <speak>
    <say-as interpret-as="expletive">censor this</say-as>
  </speak>
      

• unit

  Converts units to singular or plural depending on the number. The following example is spoken as "10 feet":

  <speak>
    <say-as interpret-as="unit">10 foot</say-as>
  </speak>
      

• time

  The following example is spoken as "Two thirty P.M.":

  <speak>
    <say-as interpret-as="time" format="hms12">2:30pm</say-as>
  </speak>
      

  The format attribute is a sequence of time field character codes. Supported field character codes in format are {h,m, s, Z, 12, 24} for hour, minute (of the hour), second (of the minute), time zone, 12-hour time, and 24-hour time respectively. If the field code appears once for hour, minute, or second then the number of digits expected are 1, 2, and 2 respectively. If the field code is repeated then the number of expected digits is the number of times the code is repeated. Fields in the time text may be separated by punctuation and/or spaces. If hour, minute, or second are not specified in the format or there are no matching digits then the field is treated as a zero value. The default format is "hms12".

  The detail attribute controls whether the spoken form of the time is 12-hour time or 24-hour time. The spoken form is 24-hour time if detail='1' or if detail is omitted and the format of the time is 24-hour time. The spoken form is 12-hour time if detail='2' or if detail is omitted and the format of the time is 12-hour time.

To learn more about the say-as element, see the W3 specification.

<audio>

Supports the insertion of recorded audio files and the insertion of other audio formats in conjunction with synthesized speech output.

Attributes

The following are the currently supported settings for audio:

• Format: MP3 (MPEG v2)
  • 24K samples per second
  • 24K ~ 96K bits per second, fixed rate
• Format: Opus in Ogg
  • 24K samples per second (super-wideband)
  • 24K - 96K bits per second, fixed rate
• Format (deprecated): WAV (RIFF)
  • PCM 16-bit signed, little endian
  • 24K samples per second
• For all formats:
  • Single channel is preferred, but stereo is acceptable.
  • 240 seconds maximum duration. If you want to play audio with a longer duration, consider implementing a media response.
  • 5 megabyte file size limit.
  • Source URL must use HTTPS protocol.
  • Our UserAgent when fetching the audio is "Google-Speech-Actions".

The contents of the <audio> element are optional and are used if the audio file cannot be played or if the output device does not support audio. The contents may include a <desc> element in which case the text contents of that element are used for display. For more information, see the Recorded Audio section in the Responses Checklist.

The src URL must also be an https URL (Google Cloud Storage can host your audio files on an https URL).

To learn more about media responses, see the media response section in the Responses guide.

To learn more about the audio element, see the W3 specification.

Example

<speak>
  <audio src="cat_purr_close.ogg">
    <desc>a cat purring</desc>
    PURR (sound didn't load)
  </audio>
</speak>

<p>,<s>

Sentence and paragraph elements.

To learn more about the p and s elements, see the W3 specification.

Example

<p><s>This is sentence one.</s><s>This is sentence two.</s></p>

Best practices

• Use <s>...</s> tags to wrap full sentences, especially if they contain SSML elements that change prosody (that is, <audio>, <break>, <emphasis>, <par>, <prosody>, <say-as>, <seq>, and <sub>).
• If a break in speech is intended to be long enough that you can hear it, use <s>...</s> tags and put that break between sentences.

<sub>

Indicate that the text in the alias attribute value replaces the contained text for pronunciation.

You can also use the sub element to provide a simplified pronunciation of a difficult-to-read word. The last example below demonstrates this use case in Japanese.

To learn more about the sub element, see the W3 specification.

Examples

<sub alias="World Wide Web Consortium">W3C</sub>

<sub alias="にっぽんばし">日本橋</sub>

<mark>

An empty element that places a marker into the text or tag sequence. It can be used to reference a specific location in the sequence or to insert a marker into an output stream for asynchronous notification.

To learn more about the mark element, see the W3 specification.

Example

<speak>
Go from <mark name="here"/> here, to <mark name="there"/> there!
</speak>

<prosody>

Used to customize the pitch, speaking rate, and volume of text contained by the element. Currently the rate, pitch, and volume attributes are supported.

The rate and volume attributes can be set according to the W3 specifications. There are three options for setting the value of the pitch attribute:

To learn more about the prosody element, see the W3 specification.

Example

The following example uses the <prosody> element to speak slowly at 2 semitones lower than normal:

<prosody rate="slow" pitch="-2st">Can you hear me now?</prosody>

<emphasis>

Used to add or remove emphasis from text contained by the element. The <emphasis> element modifies speech similarly to <prosody>, but without the need to set individual speech attributes.

This element supports an optional "level" attribute with the following valid values:

• strong
• moderate
• none
• reduced

To learn more about the emphasis element, see the W3 specification.

Example

The following example uses the <emphasis> element to make an announcement:

<emphasis level="moderate">This is an important announcement</emphasis>

<par>

A parallel media container that allows you to play multiple media elements at once. The only allowed content is a set of one or more <par>, <seq>, and <media> elements. The order of the <media> elements is not significant.

Unless a child element specifies a different begin time, the implicit begin time for the element is the same as that of the <par> container. If a child element has an offset value set for its begin or end attribute, the element's offset will be relative to the beginning time of the <par> container. For the root <par> element, the begin attribute is ignored and the beginning time is when SSML speech synthesis process starts generating output for the root <par> element (i.e. effectively time "zero").

Example

<speak>
  <par>
    <media xml:id="question" begin="0.5s">
      <speak>Who invented the Internet?</speak>
    </media>
    <media xml:id="answer" begin="question.end+2.0s">
      <speak>The Internet was invented by cats.</speak>
    </media>
    <media begin="answer.end-0.2s" soundLevel="-6dB">
      <audio
        src="https://actions.google.com/.../cartoon_boing.ogg"/>
    </media>
    <media repeatCount="3" soundLevel="+2.28dB"
      fadeInDur="2s" fadeOutDur="0.2s">
      <audio
        src="https://actions.google.com/.../cat_purr_close.ogg"/>
    </media>
  </par>
</speak>

<seq>

A sequential media container that allows you to play media elements one after another. The only allowed content is a set of one or more <seq>, <par>, and <media> elements. The order of the media elements is the order in which they are rendered.

The begin and end attributes of child elements can be set to offset values (see Time Specification below). Those child elements' offset values will be relative to the end of the previous element in the sequence or, in the case of the first element in the sequence, relative to the beginning of its <seq> container.

Example

<speak>
  <seq>
    <media begin="0.5s">
      <speak>Who invented the Internet?</speak>
    </media>
    <media begin="2.0s">
      <speak>The Internet was invented by cats.</speak>
    </media>
    <media soundLevel="-6dB">
      <audio
        src="https://actions.google.com/.../cartoon_boing.ogg"/>
    </media>
    <media repeatCount="3" soundLevel="+2.28dB"
      fadeInDur="2s" fadeOutDur="0.2s">
      <audio
        src="https://actions.google.com/.../cat_purr_close.ogg"/>
    </media>
  </seq>
</speak>

<media>

Represents a media layer within a <par> or <seq> element. The allowed content of a <media> element is an SSML <speak> or <audio> element. The following table describes the valid attributes for a <media> element.

Attributes

Time specification

A time specification, used for the value of `begin` and `end` attributes of <media> elements and media containers (<par> and <seq> elements), is either an offset value (for example, +2.5s) or a syncbase value (for example, foo_id.end-250ms).

• Offset value - Time offset value is an SMIL Timecount-value that allows values that match the regular expression: "\s\*(+|-)?\s\*(\d+)(\.\d+)?(h|min|s|ms)?\s\*"

  The first digit string is the whole part of the decimal number and the second digit string is the decimal fractional part. The default sign (i.e. "(+|-)?") is "+". The unit values correspond to hours, minutes, seconds, and milliseconds respectively. The default for the units is "s" (seconds).

• Syncbase value - A syncbase value is an SMIL syncbase-value that allows values that match the regular expression: "([-_#]|\p{L}|\p{D})+\.(begin|end)\s\*(+|-)\s\*(\d+)(\.\d+)?(h|min|s|ms)?\s\*"

  The digits and units are interpreted in the same way as an offset value.

TTS simulator

The Actions console includes a TTS simulator that you can use to test SSML with any of the above elements. You can find the TTS simulator in the console under Simulator > Audio. Type your text and SSML in the simulator and click Update and Listen to hear the TTS output.

You can also click the download button to save an .mp3 file of your TTS output.