How to encode audio for Alexa Voice?

Question

I would like to use Amazon's Alexa Voice Service (AVS) but when I use the Recognize Speech Request all I get back is "{message: null}". Authentication works, request seems to be correct because I've received error messages from the API when authentication failed or request was malformed.

I have a wav audio file, 16000 Hz, 1 channel, and use PHP's base64_encode() to encode the wav file's content.

For the audio file the AVS documentation only says Type: Binary Data. Represents the data for the audio.

Here's the request I'm sending:

Headers

POST /v1/avs/speechrecognizer/recognize HTTP/1.1
Host: access-alexa-na.amazon.com
Content-Type: multipart/form-data; boundary=86371ffc080fbb6fc614e8e36d0b8a4d
Authorization: Bearer Atza|IQEBL... (valid token)
Transfer-Encoding: chunked
Cache-Control: no-cache

Body

--86371ffc080fbb6fc614e8e36d0b8a4d
Content-Disposition: form-data; name="request"
Content-Type: application/json; charset=UTF-8

{
    "messageHeader": {
        "deviceContext": [
            {
                "name":"playbackState",
                "namespace":"AudioPlayer",
                "payload": {
                    "streamId": "xxxxxxxxxxxx",
                    "offsetInMilliseconds": "xxxxxxxxxxxx",
                    "playerActivity": "xxxxxxxxxxxx"
                }
            }
        ]
    },
    "messageBody": {
        "profile": "alexa-close-talk",
        "locale": "en-us",
        "format": "audio/L16; rate=16000; channels=1"
    }
}

--86371ffc080fbb6fc614e8e36d0b8a4d
Content-Disposition: form-data; name="audio"
Content-Type: audio/L16; rate=16000; channels=1

SUQzAgAAAAAQS1RUMgAAFwBhb...(truncated result of base64_encode(file.wav))
--86371ffc080fbb6fc614e8e36d0b8a4d--

Any idea what's wrong/missing?

score 0 · Accepted Answer · answered Sep 20 '15 at 23:32

0

The encoding for the audio file should be Linear PCM not base 64. Hope this helps

answered Sep 20 '15 at 23:32

user2636368

622
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Excuse this rather stupid question, but would I just copy the binary file contents in the post body (like `5249 4646 b80a 0200 5741 5645 666d 7420...`)? – daniel Sep 21 '15 at 06:34

Miguel Mota · Answer 2 · 2016-01-18T06:14:20.480

0

The POST body should contain the raw audio binary data. You can use a tool like sox to convert the audio to the format AVS is expecting it in which is mono channel, 16k Hz sample rate, signed 16 bit PCM.

edited Jan 18 '16 at 06:14

answered Nov 28 '15 at 06:42

Miguel Mota

20,135
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How to encode audio for Alexa Voice?

2 Answers2