synthesizeSpeech method
Synthesizes UTF-8 input, plain text or SSML, to a stream of bytes. SSML input must be valid, well-formed SSML. Some alphabets might not be available with all the voices (for example, Cyrillic might not be read at all by English voices) unless phoneme mapping is used. For more information, see How it Works.
May throw EngineNotSupportedException.
May throw InvalidSampleRateException.
May throw InvalidSsmlException.
May throw LanguageNotSupportedException.
May throw LexiconNotFoundException.
May throw MarksNotSupportedForFormatException.
May throw ServiceFailureException.
May throw SsmlMarksNotSupportedForTextTypeException.
May throw TextLengthExceededException.
Parameter outputFormat :
The format in which the returned output will be encoded. For audio stream,
this will be mp3, ogg_vorbis, ogg_opus, mu-law, a-law or pcm. For speech
marks, this will be json.
When pcm is used, the content returned is audio/pcm in a signed 16-bit, 1 channel (mono), little-endian format.
Parameter text :
Input text to synthesize. If you specify ssml as the
TextType, follow the SSML format for the input text.
Parameter voiceId :
Voice ID to use for the synthesis. You can get a list of available voice
IDs by calling the DescribeVoices
operation.
Parameter engine :
Specifies the engine (standard, neural,
long-form, or generative) for Amazon Polly to
use when processing input text for speech synthesis. Provide an engine
that is supported by the voice you select. If you don't provide an engine,
the standard engine is selected by default. If a chosen voice isn't
supported by the standard engine, this will result in an error. For
information on Amazon Polly voices and which voices are available for each
engine, see Available
Voices.
Parameter languageCode :
Optional language code for the Synthesize Speech request. This is only
necessary if using a bilingual voice, such as Aditi, which can be used for
either Indian English (en-IN) or Hindi (hi-IN).
If a bilingual voice is used and no language code is specified, Amazon
Polly uses the default language of the bilingual voice. The default
language for any voice is the one returned by the DescribeVoices
operation for the LanguageCode parameter. For example, if no
language code is specified, Aditi will use Indian English rather than
Hindi.
Parameter lexiconNames :
List of one or more pronunciation lexicon names you want the service to
apply during synthesis. Lexicons are applied only if the language of the
lexicon is the same as the language of the voice. For information about
storing lexicons, see PutLexicon.
Parameter sampleRate :
The audio frequency specified in Hz.
The valid values for mp3 and ogg_vorbis are "8000", "16000", "22050", "24000", "44100" and "48000". The default value for standard voices is "22050". The default value for neural voices is "24000". The default value for long-form voices is "24000". The default value for generative voices is "24000".
Valid values for pcm are "8000" and "16000" The default value is "16000".
Valid value for ogg_opus is "48000".
Valid value for mu-law and a-law is "8000".
Parameter speechMarkTypes :
The type of speech marks returned for the input text.
Parameter textType :
Specifies whether the input text is plain text or SSML. The default value
is plain text. For more information, see Using
SSML.
Implementation
Future<SynthesizeSpeechOutput> synthesizeSpeech({
required OutputFormat outputFormat,
required String text,
required VoiceId voiceId,
Engine? engine,
LanguageCode? languageCode,
List<String>? lexiconNames,
String? sampleRate,
List<SpeechMarkType>? speechMarkTypes,
TextType? textType,
}) async {
final $payload = <String, dynamic>{
'OutputFormat': outputFormat.value,
'Text': text,
'VoiceId': voiceId.value,
if (engine != null) 'Engine': engine.value,
if (languageCode != null) 'LanguageCode': languageCode.value,
if (lexiconNames != null) 'LexiconNames': lexiconNames,
if (sampleRate != null) 'SampleRate': sampleRate,
if (speechMarkTypes != null)
'SpeechMarkTypes': speechMarkTypes.map((e) => e.value).toList(),
if (textType != null) 'TextType': textType.value,
};
final response = await _protocol.sendRaw(
payload: $payload,
method: 'POST',
requestUri: '/v1/speech',
exceptionFnMap: _exceptionFns,
);
return SynthesizeSpeechOutput(
audioStream: await response.stream.toBytes(),
contentType:
_s.extractHeaderStringValue(response.headers, 'Content-Type'),
requestCharacters: _s.extractHeaderIntValue(
response.headers, 'x-amzn-RequestCharacters'),
);
}