SSML

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

Markup

<speak>
  Here are <say-as interpret-as="characters">SSML</say-as> samples.
  I can pause <break time="3s"/>.
  I can play a sound
  <audio src="https://www.example.com/MY_MP3_FILE.mp3">didn't get your MP3 audio file</audio>.
  I can speak in cardinals. Your number is <say-as interpret-as="cardinal">10</say-as>.
  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. The digits for ten are <say-as interpret-as="characters">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

Support for SSML elements

The following table describes the SSML elements that you can use:

Element Description
<speak>

The root element of the SSML response. The following example shows how to use the <speak> element:

<speak>
  my SSML content
</speak>

For more information, see speak Element.

<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 baesd on the linguistic context.

This element accepts two optional attributes:

  • time: Sets the length of the break by seconds or milliseconds (e.g. "3s" or "250ms").
  • strength: Sets the strength of the output's prosodic break by relative terms. Valid values are: "x-weak", weak", "medium", "strong", and "x-strong". The value "none" indicates that no prosodic break boundary should be outputted, which can be used to prevent a prosodic break that the processor would otherwise produce. The other values indicate monotonically non-decreasing (conceptually increasing) break strength between tokens. The stronger boundaries are typically accompanied by pauses.

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>

For more information, see break Element.

<say‑as>

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. The interpret-as attribute supports the following values:

  • 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>
    
  • characters
  • The following example is spoken as "C A N":

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

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

For more information, see say-as Element.

<audio>

Supports the insertion of recorded audio files and the insertion of other audio formats in conjunction with synthesized speech output. The following attributes are supported:

attribute required default values
src yes n/a A URI referring to the audio media source. Supported protocol is https.
clipBegin no 0 A TimeDesignation that is the offset from the audio source's beginning to start playback from. If this value is greater than or equal to the audio source's actual duration, then no audio is inserted.
clipEnd no infinity A TimeDesignation that is the offset from the audio source's beginning to end playback at. If the audio source's actual duration is less than this value, then playback ends at that time. If clipBegin is greater than or equal to clipEnd, then no audio is inserted.
speed no 100% The ratio output playback rate relative to the normal input rate expressed as a percentage. The format is a positive Real Number followed by %. The currently supported range is [50% (slow - half speed), 200% (fast - double speed)]. Values outside that range may (or may not) be adjusted to be within it.
repeatCount no 1, or 10 if repeatDur is set A Real Number specifying how many times to insert the audio (after clipping, if any, by clipBegin and/or clipEnd). Fractional repetitions aren't supported, so the value will be rounded to the nearest integer. Zero is not a valid value and is therefore treated as being unspecified and has the default value in that case.
repeatDur no infinity A TimeDesignation that is a limit on the duration of the inserted audio after the source is processed for clipBegin, clipEnd, repeatCount, and speed attributes (rather then the normal playback duration). If the duration of the processed audio is less than this value, then playback ends at that time.
soundLevel no +0dB Adjust the sound level of the audio by soundLevel decibels. Maximum range is +/-40dB but actual range may be effectively less, and output quality may not yield good results over the entire range.

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.
    • 120 seconds maximum duration.
    • 5 megabyte file size limit.
    • Source URL must use HTTPS protocol.
    • Our UserAgent when fetching the audio is "Google-Speech-Actions".

The following example outputs the sound stored at the src URL:

<speak>
  <audio src="https://actions.google.com/sounds/v1/animals/cat_purr_close.ogg"">
    <desc>a cat purring</desc>
    PURR (sound didn't load)
  </audio>
</speak>

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).

For more information, see audio Element.

<p>,<s>

Sentence and paragraph elements.

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

For more information, see p and s Elements.

<sub>

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

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

For more information, see sub Element.

<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:

  • Relative: Specify a relative value (e.g. "low", "medium", "high", etc) where "medium" is the default pitch.
  • Semitones: Increase or decrease pitch by "N" semitones using "+Nst" or "-Nst" respectively. Note that "+/-" and "st" are required.
  • Percentage: Increase or decrease pitch by "N" percent by using "+N%" or "-N%" respectively. Note that "%" is required but "+/-" is optional.

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>

For more information, see prosody Element.

<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

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

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

For more information, see emphasis Element.

<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").

<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.

<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 media to be rendered. 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.

attribute required default values
xml:id no no value A unique XML identifier for this element. Encoded entities are not supported. The allowed identifier values match the regular expression "([-_#]|\p{L}|\p{D})+". See XML-ID for more information.
begin no 0 The beginning time for this media container. Ignored if this is the root media container element (treated the same as the default of "0"). See the Time specification section below for valid string values.
end no no value A specification for the ending time for this media container. See the Time specification section below for valid string values.
repeatCount no 1 A Real Number specifying how many times to insert the media. Fractional repetitions aren't supported, so the value will be rounded to the nearest integer. Zero is not a valid value and is therefore treated as being unspecified and has the default value in that case.
repeatDur no no value A TimeDesignation that is a limit on the duration of the inserted media. If the duration of the media is less than this value, then playback ends at that time.
soundLevel no +0dB Adjust the sound level of the audio by soundLevel decibels. Maximum range is +/-40dB but actual range may be effectively less, and output quality may not yield good results over the entire range.
fadeInDur no 0s A TimeDesignation over which the media will fade in from silent to the optionally-specified soundLevel. If the duration of the media is less than this value, the media will be mid-fade in at the end of playback.
fadeOutDur no 0s A TimeDesignation over which the media will fade out from the optionally-specified soundLevel until it is silent. If the duration of the media is less than this value, the media will be mid-fade out at the beginning of playback.

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.