CEA Broadcast Audio and Streaming Standards 2

Question 1

What audio codec does Apple Music use for its lossless streaming tier?

Accepted Answer

ALAC (Apple Lossless Audio Codec)

Answer

Apple Music Lossless uses ALAC (Apple Lossless Audio Codec) at CD quality (16-bit / 44.1 kHz) and Hi-Res Lossless up to 24-bit / 192 kHz. ALAC is Apple's proprietary lossless codec, supported natively on all Apple devices.

Question 2

What is the HLS (HTTP Live Streaming) audio codec and container used for adaptive bitrate audio delivery?

Accepted Answer

HLS supports AAC audio in MPEG-2 Transport Stream (.ts) or MPEG-4 (.mp4/fMP4) containers, with multiple bitrate renditions for adaptive streaming

Answer

HLS (HTTP Live Streaming), developed by Apple, uses AAC audio encapsulated in MPEG-2 TS segments or fMP4 containers. It supports multiple audio bitrate renditions allowing clients to adaptively switch quality based on available bandwidth. It is the dominant protocol for live and on-demand streaming.

Question 3

What is the Netflix audio loudness specification for streaming content delivery?

Accepted Answer

-27 LKFS with max true peak of -2 dBTP

Answer

Netflix specifies -27 LKFS integrated loudness with a maximum true peak of -2 dBTP for streaming content delivery. This is lower than music streaming targets, reflecting the dynamic nature of cinematic content (dialogue, music, and sound effects) requiring more headroom.

Question 4

What is the 'Opus' codec and what makes it suitable for real-time streaming applications?

Accepted Answer

An open, royalty-free audio codec developed by the IETF with low algorithmic delay (as low as 2.5 ms), designed for real-time communications (VoIP, WebRTC) and low-latency streaming

Answer

Opus is an open, royalty-free codec (IETF RFC 6716) combining SILK (speech) and CELT (music) coding modes. Its very low algorithmic delay (2.5–60 ms), adaptive bitrate support (6–510 kbps), and excellent quality at low bitrates make it ideal for real-time applications including WebRTC, Discord, and gaming voice chat.

Question 5

In broadcast audio, what does 'loudness range' (LRA) measure, and what is an acceptable LRA for a broadcast drama?

Accepted Answer

LRA (EBU Tech 3342) measures the variation in short-term loudness over a program; for drama, an LRA of 10–20 LU is typical, while highly compressed programs may be below 6 LU

Answer

LRA (Loudness Range, EBU Tech 3342) quantifies the dynamic variation within a program using a statistical distribution of short-term loudness measurements. Drama and documentaries typically exhibit LRA values of 10–20 LU. Heavily processed or highly compressed content (pop music, some commercials) may show LRA below 6 LU.

(CEA) Certified Audio Engineer Practice Test

(CEA) Certified Audio Engineer Practice Test

CEA Broadcast Audio and Streaming Standards 2