3 ms·

Isn't it just the need for low latency? "Media" (music, videos etc) has good sound quality but significant latency. It gets compensated by delaying the video by

Isn't it just the need for low latency? "Media" (music, videos etc) has good sound quality but significant latency. It gets compensated by delaying the video by an equal amount, but it's too much latency for phone calls.

eptcyka 3y ago
It's Bluetooth not having enough latency.
- eptcyka 3y ago
  I meant to say bandwidth.
therein 3y ago
> It gets compensated by delaying the video by an equal amount Is this actually done? Who would be doing it, the OS? It just sounds like the separation of concerns and the design of the interfaces would make it pretty unlikely.
- explodingcamera 3y ago
  It is absolutely done, mostly by the media player/library used, e.g exoplayer on Android has automatic lag compensation for that purpose.
- magicalhippo 3y ago
  Not always. Just got some wireless headphones at work, and now I can no longer enjoy YouTube videos (mostly KEXP) because of the 100ms audio delay. It's too disturbing even only in side view. So at least with a browser on Windows it's not done.
- lxgr 3y ago
  I’ve definitely noticed it on macOS. Videos in the browser will stall for a fraction of a second after pressing play to give the audio time to catch up.
- roywashere 3y ago
  Yes, this is called AVDTP 1.3 Delay Reporting feature. It allows headphones to report the delay to a sending device that actually plays the sound.
- HPsquared 3y ago
  Empirically: videos are perfectly synced using my Sony headphones (which use Bluetooth 5.0) on Android. But anything interactive (games, and UI sound effects) has a significant delay. I think Bluetooth 5.0 includes something where the audio latency is communicated back to the phone.
  - Pxtl 3y ago
    Yeah, playing twitchy games with bluetooth on is janky suicide. I was trying to play a difficult platformer on my phone with a clipped-on game controller and it was miserable until I switched to wired audio. Not sure if it was the audio latency or the crowded traffic on bluetooth slowing down my BT game controller, but the difference in feel and success was night-and-day when I did that.
- chenxiaolong 3y ago
  Yup, Bluetooth devices can report the latency via AVDTP 1.3 Delay Reporting. If I remember correctly from the last time I looked at this, the media framework in OS's tend to expose this to applications by reporting the timestamp that a submitted audio buffer is actually played back. The video player can use these timestamps to adjust the video delay accordingly. And since it's per buffer, it can handle the latency changing (eg. by switching from Bluetooth to a wired connection). I know at least Android and Linux + Pipewire support this. I haven't encountered a single application on desktop Linux that doesn't support this properly. All the standard video players and browsers work. It works for HDMI too, when the TV/AV receiver is well designed and communicates the latency in the EDID.
  - AnssiH 3y ago
    Indeed, there is some (usually much smaller, but depending on buffer sizes) audio delay even in regular desktop systems so video players and audio APIs mostly already had proper handling for it.
- meindnoch 3y ago
  "Using an AirPlay-enabled device for your audio content can result in a 2-second delay. Check for this delay in game content." https://developer.apple.com/documentation/avfaudio/avaudiosession/1616500-outputlatency https://developer.apple.com/documentation/avfaudio/avaudiose...
amluto 3y ago
Everyone who wants a standard to require their patent is allergic to it, but Opus was designed for exactly this. It’s acoustically transparent at moderate bit rate, good enough at lower bit rate, and adds minimal latency.
- photoGrant 3y ago
  Love that profits plunder progress.
  - amluto 3y ago
    It’s true. The SBC bitrates discussed in the article are nuts. Opus is transparent at 1/5-1/4 of those rates. OTOH it’s newer and maybe ten-year-old cheap Bluetooth chips couldn’t have handled it.
    - acchow 3y ago
      What would the power requirements for decoding Opus with a low latency be? Wireless earphones have tiny batteries.
      - rickdeckard 3y ago
        Also keep in mind that you would also need realtime transcoding on the transmitter, as the device would need to mix whatever audio-codec is provided with other channels (Notification sounds, etc.) and encode it into Opus on-the-fly.
  - swells34 3y ago
    No no no, capitalism is supposed to make BETTER products, because money! You must be mistaken.
    - pasiaj 3y ago
      Better than what?
    - 3y ago

eptcyka 3y ago

It's Bluetooth not having enough latency.

eptcyka 3y ago
I meant to say bandwidth.

therein 3y ago

> It gets compensated by delaying the video by an equal amount Is this actually done? Who would be doing it, the OS? It just sounds like the separation of concerns and the design of the interfaces would make it pretty unlikely.

explodingcamera 3y ago
It is absolutely done, mostly by the media player/library used, e.g exoplayer on Android has automatic lag compensation for that purpose.
magicalhippo 3y ago
Not always. Just got some wireless headphones at work, and now I can no longer enjoy YouTube videos (mostly KEXP) because of the 100ms audio delay. It's too disturbing even only in side view. So at least with a browser on Windows it's not done.
lxgr 3y ago
I’ve definitely noticed it on macOS. Videos in the browser will stall for a fraction of a second after pressing play to give the audio time to catch up.
roywashere 3y ago
Yes, this is called AVDTP 1.3 Delay Reporting feature. It allows headphones to report the delay to a sending device that actually plays the sound.
HPsquared 3y ago
Empirically: videos are perfectly synced using my Sony headphones (which use Bluetooth 5.0) on Android. But anything interactive (games, and UI sound effects) has a significant delay. I think Bluetooth 5.0 includes something where the audio latency is communicated back to the phone.
- Pxtl 3y ago
  Yeah, playing twitchy games with bluetooth on is janky suicide. I was trying to play a difficult platformer on my phone with a clipped-on game controller and it was miserable until I switched to wired audio. Not sure if it was the audio latency or the crowded traffic on bluetooth slowing down my BT game controller, but the difference in feel and success was night-and-day when I did that.
chenxiaolong 3y ago
Yup, Bluetooth devices can report the latency via AVDTP 1.3 Delay Reporting. If I remember correctly from the last time I looked at this, the media framework in OS's tend to expose this to applications by reporting the timestamp that a submitted audio buffer is actually played back. The video player can use these timestamps to adjust the video delay accordingly. And since it's per buffer, it can handle the latency changing (eg. by switching from Bluetooth to a wired connection). I know at least Android and Linux + Pipewire support this. I haven't encountered a single application on desktop Linux that doesn't support this properly. All the standard video players and browsers work. It works for HDMI too, when the TV/AV receiver is well designed and communicates the latency in the EDID.
- AnssiH 3y ago
  Indeed, there is some (usually much smaller, but depending on buffer sizes) audio delay even in regular desktop systems so video players and audio APIs mostly already had proper handling for it.
meindnoch 3y ago
"Using an AirPlay-enabled device for your audio content can result in a 2-second delay. Check for this delay in game content." https://developer.apple.com/documentation/avfaudio/avaudiosession/1616500-outputlatency https://developer.apple.com/documentation/avfaudio/avaudiose...

amluto 3y ago

Everyone who wants a standard to require their patent is allergic to it, but Opus was designed for exactly this. It’s acoustically transparent at moderate bit rate, good enough at lower bit rate, and adds minimal latency.

photoGrant 3y ago
Love that profits plunder progress.
- amluto 3y ago
  It’s true. The SBC bitrates discussed in the article are nuts. Opus is transparent at 1/5-1/4 of those rates. OTOH it’s newer and maybe ten-year-old cheap Bluetooth chips couldn’t have handled it.
  - acchow 3y ago
    What would the power requirements for decoding Opus with a low latency be? Wireless earphones have tiny batteries.
    - rickdeckard 3y ago
      Also keep in mind that you would also need realtime transcoding on the transmitter, as the device would need to mix whatever audio-codec is provided with other channels (Notification sounds, etc.) and encode it into Opus on-the-fly.
- swells34 3y ago
  No no no, capitalism is supposed to make BETTER products, because money! You must be mistaken.
  - pasiaj 3y ago
    Better than what?
  - 3y ago