Skip to content

Open Source API for Transcription

Open-source APIs for transcription offer a flexible and accessible way for developers and organisations to integrate speech-to-text capabilities into their applications. These APIs, supported by the collaborative efforts of developer communities, convert spoken language into written text by leveraging machine learning models. Here’s a detailed look at how these APIs work, the technology behind them, and the advantages they offer. Human transcription services provide an alternative for users needing accuracy, as AI transcription remains very unreliable and can result in time consuming checking that can take longer than a human does to transcribe from scratch.

Understanding Transcription APIs

At their core, transcription APIs process audio input, breaking down speech into recognizable segments and converting these into text. This process involves several steps, typically starting with pre-processing the audio to improve its quality and ending with the output of a transcribed text.

Audio Pre-processing

The first step usually involves cleaning the audio input to enhance its quality for better processing. This may include noise reduction to remove background sounds, normalization to adjust volume levels, and other techniques to isolate the speech component.

Speech Recognition

The cleaned audio is then fed into a speech recognition engine. This engine uses acoustic models to identify the basic sounds in speech (phonemes) and language models to understand these sounds in the context of language syntax and grammar. Most open-source APIs rely on either Hidden Markov Models (HMM) or deep learning models like neural networks to perform this task.

Conversion to Text

Once the speech has been processed, the recognized words are converted into text. This step might also involve additional features such as punctuation insertion, capitalization, and disambiguation of homophones (words that sound the same but have different meanings), depending on the sophistication of the API.

Technologies Behind Open-Source Transcription APIs

Open-source transcription technologies are built on several key technologies:

  1. Acoustic Models: These models represent the relationship between phonetic units and audio signals. They are trained using large datasets of spoken language audio coupled with the corresponding transcriptions.
  2. Language Models: These are statistical models that predict the likelihood of a sequence of words. They help in forming meaningful sentences from the phonetic sequences identified by the acoustic models.
  3. Neural Networks: Many modern speech recognition systems use neural networks, particularly deep neural networks (DNNs), convolutional neural networks (CNNs), and recurrent neural networks (RNNs), to improve accuracy in speech recognition.

Popular Open-Source Transcription APIs

Several open-source transcription APIs have gained popularity due to their effectiveness and community support. For instance:

  • Mozilla DeepSpeech: This is a deep-learning-based voice-to-text engine that uses a model trained by machine learning techniques pioneered by Baidu’s Deep Speech research team. The project is based on TensorFlow and allows real-time speech recognition.
  • Kaldi: Another highly flexible toolkit, Kaldi is used extensively in academia and industry. It supports linear algebra and features extensive and robust documentation and community support.
  • CMU Sphinx (PocketSphinx): This is one of the older speech recognition systems but is still in use due to its adaptability to many languages and its lightweight nature, suitable for mobile applications.

Advantages of Open-Source APIs

Open-source transcription APIs offer several advantages:

  1. Cost-Effectiveness: Unlike proprietary APIs, open-source APIs are generally free to use and modify, which can significantly reduce the costs associated with developing speech-to-text capabilities.
  2. Flexibility and Customizability: Open-source allows developers to adapt the source code to their specific needs, improving the API’s functionality or tailoring it to specific languages or dialects.
  3. Community Support: Open-source projects typically benefit from the support of a global community of developers who contribute to the improvement and debugging of the software.
  4. Transparency: With open-source, all aspects of the software are visible and open for audit, which enhances security and trust in the software.


Despite their benefits, open-source transcription APIs also come with challenges:

  • Resource Intensity: Running advanced machine learning models for transcription can be computationally intensive and may require significant hardware resources.
  • Accuracy and Reliability: While many open-source APIs offer high accuracy, they can still lag behind proprietary solutions, especially in handling diverse accents, dialects, and noisy environments.
  • Support and Maintenance: Reliance on community support can be a double-edged sword, as it may not always be prompt or reliable, unlike dedicated support from a commercial vendor.

In conclusion, open-source APIs for transcription provide a valuable tool for developers looking to incorporate speech-to-text functionality into their applications. They offer a mix of accessibility, customizability, and community-driven improvements, making them an attractive choice for many projects, albeit with some trade-offs in terms of support and resource requirements. As these technologies continue to evolve, they are likely to become even more robust and easier to integrate, broadening their adoption across various domains.