Hiring guide for Opus Engineers

Opus Developer Hiring Guide

Opus is a historical computer programming language developed in the late 1960s by Control Data Corporation (CDC). It was designed for use on CDC's series of mainframe computers, specifically the CDC 6600 model. As an assembly language, Opus allowed programmers to write low-level code that directly manipulated the hardware of these machines. The development and usage of Opus were integral parts of early computing history and played a significant role in advancing software technology. Information about this programming language can be found in various technical reports from CDC and other historical documents related to early computer science.

Ask the right questions secure the right Opus talent among an increasingly shrinking pool of talent.

First 20 minutes

General Opus app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Opus application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you describe the basic structure of an Opus file?
An Opus file is composed of a sequence of pages from an Ogg bitstream. Each page is a self-contained entity carrying audio data and associated information. The pages are grouped into logical bitstreams, each corresponding to an encoded audio stream.
What are the key features of Opus that make it suitable for interactive speech and audio transmission over the internet?
Opus has low latency, making it suitable for real-time applications. It also has high compression efficiency, which allows for high-quality audio transmission even over low-bandwidth connections. Additionally, Opus supports both speech and music, making it versatile for different audio content.
Describe the difference between Opus and other audio codecs like MP3 or AAC.
Opus is designed for interactive speech and audio transmission over the Internet, while MP3 and AAC are typically used for storing music. Opus has lower latency and better compression efficiency than MP3 and AAC, making it more suitable for real-time applications.
How would you handle packet loss when transmitting Opus audio over a network?
Opus has built-in packet loss concealment feature. If a packet is lost, the decoder can generate a plausible substitute for the missing data based on the information in the received packets.
What are the main components of the Opus encoder and how do they work together?
The Opus encoder consists of a signal analysis part, a bit allocation part, and a quantization and coding part. The signal analysis part analyzes the input audio and determines the best way to encode it. The bit allocation part decides how many bits to use for each part of the audio. The quantization and coding part then encodes the audio using the allocated bits.
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What you’re looking for early on

Does the candidate have a solid understanding of Opus?
Has the candidate demonstrated problem-solving skills?
Can the candidate communicate effectively?
Does the candidate have relevant experience with similar projects?

Next 20 minutes

Specific Opus development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

How would you optimize the performance of an Opus encoder for a specific application?
The performance of an Opus encoder can be optimized by tuning the encoder parameters, such as the bit rate, frame size, and complexity. The optimal settings depend on the specific requirements of the application, such as the available bandwidth, latency constraints, and audio quality requirements.
Describe the difference between the SILK and CELT modes in Opus.
SILK is designed for speech and provides better quality for lower bit rates, while CELT is designed for general audio and provides better quality for higher bit rates. Opus can switch between SILK and CELT dynamically depending on the audio content.
What are the challenges in implementing an Opus decoder and how would you overcome them?
Implementing an Opus decoder can be challenging due to the complexity of the Opus codec. This can be overcome by understanding the Opus specification thoroughly and using a well-structured and modular programming approach. Testing the decoder with a wide range of audio inputs is also important to ensure robustness.
How would you test the performance of an Opus encoder or decoder?
The performance of an Opus encoder or decoder can be tested by measuring the audio quality, encoding or decoding speed, and resource usage. Audio quality can be measured using objective metrics like PESQ or POLQA, or subjective listening tests. Encoding or decoding speed can be measured using benchmarking tools. Resource usage can be measured using profiling tools.
How would you integrate an Opus encoder or decoder into a larger system, such as a VoIP application or a media player?
An Opus encoder or decoder can be integrated into a larger system by using the Opus API. The system needs to provide the input audio data to the encoder or decoder, and handle the output audio data. The system also needs to manage the encoder or decoder state and control the encoder or decoder parameters.
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The ideal back-end app developer

What you’re looking to see on the Opus engineer at this point.

At this point, a skilled Opus engineer should demonstrate strong problem-solving abilities, proficiency in Opus programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Opus.

What does this simple code snippet do in Opus?
PROGRAM HelloWorld
  PRINT "Hello, World!"
This is a basic Opus code snippet that prints the string 'Hello, World!' to the console.
What does this Opus code snippet do?
PROGRAM Calculate
  INTEGER a = 5
  INTEGER b = 10
  PRINT a + b
This code snippet declares two integer variables 'a' and 'b', assigns them the values 5 and 10 respectively, and then prints the sum of 'a' and 'b' to the console.
What does this Opus code snippet do?
PROGRAM ArrayManipulation
  INTEGER ARRAY numbers = [1, 2, 3, 4, 5]
  FOR EACH num IN numbers
    PRINT num * 2
This code snippet declares an integer array 'numbers', and then iterates over each number in the array, printing the number multiplied by 2 to the console.
What does this Opus code snippet do?
PROGRAM Threading
  THREAD t = NEW THREAD(PrintNumbers)
  SUBROUTINE PrintNumbers
    FOR i = 1 TO 10
      PRINT i
This code snippet creates a new thread 't' that runs the subroutine 'PrintNumbers', which prints the numbers 1 through 10 to the console. The thread 't' is started with the 'START' method.

Wrap-up questions

Final candidate for Opus Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Opus application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

Describe the difference between constant bit rate (CBR) and variable bit rate (VBR) in Opus.
In CBR, the bit rate is kept constant over time, which is simple and predictable, but may not provide the best audio quality. In VBR, the bit rate can vary over time to provide better audio quality, but is less predictable and may require more sophisticated buffering and bandwidth management.
How would you handle audio signal pre-processing in Opus?
Opus has built-in support for audio signal pre-processing, such as noise suppression and automatic gain control. These features can be controlled using the Opus API. The optimal settings depend on the specific requirements of the application and the characteristics of the input audio signal.
What are the considerations in choosing the frame size in Opus?
The frame size in Opus affects the latency and the audio quality. A smaller frame size provides lower latency, but may result in lower audio quality. A larger frame size provides higher audio quality, but may result in higher latency. The optimal frame size depends on the specific requirements of the application.

Opus application related

Product Perfect's Opus development capabilities

Beyond hiring for your Opus engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Opus projects, and can engage in multiple capacities.