Wireless Audio Protocols AirPlay 2 / Google Cast / Spotify Connect / Tidal Connect

The four major protocols

AirPlay 2 is Apple's Wi-Fi-based wireless streaming protocol for audio (and, where supported, video) with simultaneous multi-room playback. It shipped to consumers as part of iOS 11.4 on May 29, 2018, after being announced at WWDC the previous year.

Google Cast is Google's Wi-Fi-based casting protocol used to send audio and video from a controller — a phone, tablet, or browser — to a target device such as a speaker, display, or AVR. The on-device branding was renamed from Chromecast built-in to Google Cast in 2024, but the underlying protocol is the same.

Spotify Connect launched on September 2, 2013 at IFA Berlin with ten initial hardware partners — Argon, Bang & Olufsen, Denon, Hama, Marantz, Philips, Pioneer, Revo, Teufel, and Yamaha — using chipsets from SMSC and Frontier Silicon.

Tidal Connect launched on October 20, 2020 as Tidal's own casting protocol — parallel in design to Spotify Connect but built to carry Tidal's higher-tier formats. Initial partners spanned BluOS-enabled players from NAD Electronics, Bluesound, DALI, and Monitor Audio, with Cambridge Audio, KEF, iFi audio, Lyngdorf, and Naim Audio in the same launch wave.

All four protocols run over the local Wi-Fi network using IP — not over Bluetooth's point-to-point radio link. That difference is why they can address multiple rooms in sync, carry higher-bitrate formats than Bluetooth's A2DP codecs, and let the controlling phone leave the room (in the Connect protocols) without dropping playback.

How each protocol works

Both AirPlay 2 and Google Cast use mDNS / DNS-SD service discovery on the local Wi-Fi network — Apple's Bonjour for AirPlay (service type _airplay._tcp) and the analogous Google Cast service type (_googlecast._tcp). This is also why neither protocol crosses VLAN boundaries by default: the discovery multicasts are link-local. Spotify Connect and Tidal Connect ride on top of their own service back-ends, so the controller and endpoint find each other through the streaming service's account session rather than purely through link-local discovery.

Spotify Connect and Tidal Connect are both handoff protocols: the controlling app does not relay audio to the speaker over Wi-Fi. It tells the streaming service to redirect playback to the endpoint, and the endpoint then pulls the stream directly from Spotify's or Tidal's servers. The phone continues to act as a remote — transport, volume, search — but can leave the network entirely without interrupting playback.

AirPlay 2 and Google Cast operate in two patterns. When casting from a service-aware app — the YouTube app casting to a Chromecast, for example — the endpoint pulls the stream directly, with the phone handing off a URL plus controller role similar to the Connect protocols. When AirPlaying generic system audio from an iPhone, or casting a browser tab from Chrome, the controller actually relays the encoded audio over Wi-Fi to the endpoint. The relay path is what keeps AirPlay's iPhone-to-speaker stream limited to 16-bit/44.1 kHz even though the protocol itself can carry 24-bit/48 kHz between two HomePods.

The four protocols carry meaningfully different ceilings. AirPlay 2 tops out at 24-bit/48 kHz Apple Lossless within the protocol, but only when the source already has the lossless stream locally — HomePod-to-HomePod, for example. iPhone-to-speaker is capped at 16-bit/44.1 kHz. Google Cast supports FLAC at up to 24-bit/96 kHz on the Chromecast Audio reference target. Spotify Connect carries up to 320 kbps Ogg Vorbis on Premium. Tidal Connect carries Tidal's full HiFi catalogue including FLAC up to 24-bit/192 kHz, MQA, and Dolby Atmos.

What this means in a home-theater context

The protocol choice is audible only when the source material exceeds what the lower-ceiling transport can carry. Spotify maxes out at 320 kbps Ogg Vorbis, so any of these protocols transports it transparently. Apple Music Lossless and Tidal HiFi/Master tracks exceed CD quality, so the transport ceiling becomes the bottleneck — Tidal Connect or Google Cast (FLAC up to 24/96) preserve more of the source than AirPlay's typical 16/44 iPhone path does.

Most current networked AVRs — Denon and Marantz HEOS, Yamaha MusicCast, Sonos, Bluesound/BluOS — implement AirPlay 2 plus a subset of the others. Spotify Connect coverage is the broadest; it has been a default checkbox on hi-fi hardware since 2014. Tidal Connect coverage is narrower and concentrated among hi-fi-leaning brands; the BluOS/Bluesound, NAD, KEF, and Naim ecosystems were the launch partners. Google Cast coverage skews toward smart-speaker and mass-market AVR lines and is notably absent from Sonos's first-party platform.

The practical takeaway: if a system is built around Apple Music Lossless, the AirPlay 2 path matters and the iPhone-relay limitation is worth understanding before assuming the protocol delivers the full advertised quality. If the system is built around Tidal HiFi or Master tier, native Tidal Connect support on the endpoint matters more than AirPlay 2 support — the Tidal Connect path preserves the full ceiling.

Common misconceptions

AirPlay 1 (2010) and AirPlay 2 (2018) are different protocol revisions, not branding. AirPlay 1 streams to a single target. AirPlay 2 added simultaneous multi-room playback in sync, stereo pairing of two speakers, deeper buffering for resilience to Wi-Fi hiccups, and Siri-driven control. Older AirPlay 1 hardware does not gain AirPlay 2 features through a software update unless the manufacturer ships new firmware that implements the AirPlay 2 stack.

A common misconception is that Spotify Connect and Tidal Connect work like Bluetooth or AirPlay-system-audio — that the phone keeps streaming and the speaker is just an output device. They do not. Once the user picks a target, the speaker fetches the stream directly from the service's servers; the phone becomes a remote. The phone can lock, leave the network, or even die mid-track and playback continues on the speaker.

Bluetooth audio is sometimes lumped in with these casting protocols but is fundamentally different. Bluetooth A2DP is a point-to-point radio link between one source and one receiver; it carries lossy codecs (SBC, AAC; aptX HD or LDAC where supported); it has no native multi-room sync; and it does not survive the source leaving the room. AirPlay 2, Google Cast, Spotify Connect, and Tidal Connect all run over Wi-Fi/IP and break those constraints.

The AirPlay 2 lossless story is itself a frequent point of confusion. Apple's documentation describes the protocol as carrying lossless ALAC up to 24-bit/48 kHz, and that figure is accurate — between two HomePods sharing a stream that one of them pulled natively from Apple Music. But the typical iPhone-to-speaker path is capped at 16-bit/44.1 kHz, because the controller relays the encoded audio rather than handing off a stream URL. Both statements are true at the same time: the protocol supports up to 24/48, but the iPhone-relay path in everyday use does not exercise that capability.