CEA Broadcast Audio and Streaming Standards 2 — Questions and Answers
Question 1: What audio codec does Apple Music use for its lossless streaming tier?
- FLAC (Free Lossless Audio Codec)
- ALAC (Apple Lossless Audio Codec) (Correct answer)
- Dolby TrueHD
- PCM WAV at 16-bit / 44.1 kHz
Correct answer: ALAC (Apple Lossless Audio Codec)
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?
- HLS uses MP3 in a .ts container exclusively
- HLS supports AAC audio in MPEG-2 Transport Stream (.ts) or MPEG-4 (.mp4/fMP4) containers, with multiple bitrate renditions for adaptive streaming (Correct answer)
- HLS is limited to lossless FLAC delivery at a single fixed bitrate
- HLS uses Opus at 48 kHz in an Ogg container for all streaming applications
Correct answer: HLS supports AAC audio in MPEG-2 Transport Stream (.ts) or MPEG-4 (.mp4/fMP4) containers, with multiple bitrate renditions for adaptive streaming
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?
- -24 LKFS with max true peak of -2 dBTP
- -14 LUFS with max true peak of -1 dBTP
- -27 LKFS with max true peak of -2 dBTP (Correct answer)
- -16 LUFS with max true peak of -1 dBTP
Correct answer: -27 LKFS with max true peak of -2 dBTP
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?
- A lossless codec developed by Dolby for cinema streaming, requiring a hardware decoder
- 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 (Correct answer)
- A high-resolution audio format standardized by the EBU for broadcast monitoring
- A multi-channel surround codec replacing AAC in the DASH streaming standard
Correct 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
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?
- LRA measures the peak-to-loudness ratio of the entire program; acceptable LRA for drama is below 1 LU
- 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 (Correct answer)
- LRA measures the average loudness across the dialogue track only, excluding music and effects
- LRA is equivalent to the dynamic range (DR) value; broadcast drama should target DR-14 or higher
Correct 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
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.
Question 6: What is 'MPEG-DASH' and how does it handle audio in adaptive streaming?
- A physical media delivery standard for optical disc broadcast mastering
- A W3C/ISO adaptive bitrate streaming protocol that segments audio and video into chunks described by a manifest (MPD), supporting multiple audio representations at different bitrates for client-side adaptation (Correct answer)
- A MPEG audio codec specification used for radio broadcast at 128 kbps
- A hardware multiplexer standard for combining multiple broadcast audio streams into an SDI feed
Correct answer: A W3C/ISO adaptive bitrate streaming protocol that segments audio and video into chunks described by a manifest (MPD), supporting multiple audio representations at different bitrates for client-side adaptation
MPEG-DASH (Dynamic Adaptive Streaming over HTTP) is an open ISO standard for adaptive bitrate streaming. Audio and video are segmented and described in a Media Presentation Description (MPD) manifest. Clients dynamically select audio representation segments based on bandwidth, with support for multiple codecs (AAC, AC-4, Opus) and languages.
CEA Broadcast Audio and Streaming Standards 2
What audio codec does Apple Music use for its lossless streaming tier?