Amazon Transcribe examples using SDK for C++

The following code examples show you how to perform actions and implement common scenarios by using the AWS SDK for C++ with Amazon Transcribe.

Actions are code excerpts from larger programs and must be run in context. While actions show you how to call individual service functions, you can see actions in context in their related scenarios.

Each example includes a link to the complete source code, where you can find instructions on how to set up and run the code in context.

Actions

StartStreamTranscriptionAsync

The following code example shows how to use StartStreamTranscriptionAsync.

SDK for C++

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the AWS Code Examples Repository.

int main() {
    Aws::SDKOptions options;

    Aws::InitAPI(options);
    {
        //TODO(User): Set to the region of your AWS account.
        const Aws::String region = Aws::Region::US_WEST_2;

        //Load a profile that has been granted AmazonTranscribeFullAccess AWS managed permission policy.
        Aws::Client::ClientConfiguration config;
#ifdef _WIN32
        // ATTENTION: On Windows with the AWS C++ SDK, this example only runs if the SDK is built
        // with the curl library. 
        // For more information, see the accompanying ReadMe.
        // For more information, see "Building the SDK for Windows with curl".
        // https://docs.aws.amazon.com/sdk-for-cpp/v1/developer-guide/setup-windows.html
        //TODO(User): Update to the location of your .crt file.
        config.caFile = "C:/curl/bin/curl-ca-bundle.crt";
#endif
        config.region = region;

        TranscribeStreamingServiceClient client(config);
        StartStreamTranscriptionHandler handler;
        handler.SetOnErrorCallback(
                [](const Aws::Client::AWSError<TranscribeStreamingServiceErrors> &error) {
                        std::cerr << "ERROR: " + error.GetMessage() << std::endl;
                });
        //SetTranscriptEventCallback called for every 'chunk' of file transcripted.
        // Partial results are returned in real time.
        handler.SetTranscriptEventCallback([](const TranscriptEvent &ev) {
                for (auto &&r: ev.GetTranscript().GetResults()) {
                    if (r.GetIsPartial()) {
                        std::cout << "[partial] ";
                    }
                    else {
                        std::cout << "[Final] ";
                    }
                    for (auto &&alt: r.GetAlternatives()) {
                        std::cout << alt.GetTranscript() << std::endl;
                    }
                }
        });

        StartStreamTranscriptionRequest request;
        request.SetMediaSampleRateHertz(SAMPLE_RATE);
        request.SetLanguageCode(LanguageCode::en_US);
        request.SetMediaEncoding(
                MediaEncoding::pcm); // wav and aiff files are PCM formats.
        request.SetEventStreamHandler(handler);

        auto OnStreamReady = [](AudioStream &stream) {
                Aws::FStream file(FILE_NAME, std::ios_base::in | std::ios_base::binary);
                if (!file.is_open()) {
                    std::cerr << "Failed to open " << FILE_NAME << '\n';
                }
                std::array<char, BUFFER_SIZE> buf;
                int i = 0;
                while (file) {
                    file.read(&buf[0], buf.size());

                    if (!file)
                        std::cout << "File: only " << file.gcount() << " could be read"
                                  << std::endl;

                    Aws::Vector<unsigned char> bits{buf.begin(), buf.end()};
                    AudioEvent event(std::move(bits));
                    if (!stream) {
                        std::cerr << "Failed to create a stream" << std::endl;
                        break;
                    }
                    //The std::basic_istream::gcount() is used to count the characters in the given string. It returns
                    //the number of characters extracted by the last read() operation.
                    if (file.gcount() > 0) {
                        if (!stream.WriteAudioEvent(event)) {
                            std::cerr << "Failed to write an audio event" << std::endl;
                            break;
                        }
                    }
                    else {
                        break;
                    }
                    std::this_thread::sleep_for(std::chrono::milliseconds(
                            25)); // Slow down because we are streaming from a file.
                }
                if (!stream.WriteAudioEvent(
                        AudioEvent())) {
                    // Per the spec, we have to send an empty event (an event without a payload) at the end.
                    std::cerr << "Failed to send an empty frame" << std::endl;
                }
                else {
                    std::cout << "Successfully sent the empty frame" << std::endl;
                }
                stream.flush();
                stream.Close();
        };

        Aws::Utils::Threading::Semaphore signaling(0 /*initialCount*/, 1 /*maxCount*/);
        auto OnResponseCallback = [&signaling](
                const TranscribeStreamingServiceClient * /*unused*/,
                const Model::StartStreamTranscriptionRequest & /*unused*/,
                const Model::StartStreamTranscriptionOutcome &outcome,
                const std::shared_ptr<const Aws::Client::AsyncCallerContext> & /*unused*/) {

                if (!outcome.IsSuccess()) {
                    std::cerr << "Transcribe streaming error "
                              << outcome.GetError().GetMessage() << std::endl;
                }

                signaling.Release();
        };

        std::cout << "Starting..." << std::endl;
        client.StartStreamTranscriptionAsync(request, OnStreamReady, OnResponseCallback,
                                             nullptr /*context*/);
        signaling.WaitOne(); // Prevent the application from exiting until we're done.
        std::cout << "Done" << std::endl;
    }

    Aws::ShutdownAPI(options);

    return 0;
}

• For API details, see StartStreamTranscriptionAsync in AWS SDK for C++ API Reference.