Audio¶
In short:
- You hear your profile's language when the film has it: set it in Settings → Playback → Default Audio Language. A track you pick by hand in the player always wins.
- The sound is sent as it is when your device can play it. Otherwise the server converts it to a common format (AAC). Often the sound is the only thing converted, and the picture stays untouched.
- On a phone's speaker, headphones or Bluetooth, the Android app plays stereo. With the Android or Android TV app on HDMI, you get as many channels as the TV or amplifier accepts (5.1, for example).
- Sound out of sync with the picture? See Sound out of sync.
The rest of this page explains which track plays, when it is copied or converted, and with how many channels. The profile settings named here are in Settings → Playback.
What you will hear, by device¶
| Your device | What arrives |
|---|---|
| A browser | The track as it is when the browser decodes it; AC-3 and E-AC-3 decoded in the page (below); otherwise AAC. A surround AAC track is folded to your output by the browser. |
| An Android phone on its speaker, headphones or Bluetooth | Stereo. The app declares a stereo output, so a surround track is re-encoded to stereo by the server, with a normalised fold. Dolby Digital the app decodes itself is sent as it is and folded by the app. |
| An Android phone or Android TV on HDMI | As many channels as the HDMI sink reports it takes: a 5.1 track stays 5.1 on a 5.1 amplifier. |
| A cast receiver | What the receiver reported about its output: see Casting. |
The Android apps probe the output at each playback start: plugging headphones in takes effect at the next title, track switch or quality change, not in the middle of a scene.
Which track plays¶
A track chosen by hand, on the title page or in the player, always wins. Otherwise the players follow the profile's Default Audio Language, then the track the file marks as default, then the first one. A track flagged as commentary is skipped in favour of a regular one when the file has both.
Only the track being played is judged: a DTS track you are not listening to never causes a transcode.
Copied or re-encoded¶
The track is copied when the player decodes its codec and its output has enough channels for it, within the profile's Max Audio Channels (Stereo (2.0), Surround (5.1) or Surround (7.1)). Otherwise it is re-encoded to AAC:
- with as many channels as the source, the device and the profile allow, up to 5.1 (a 7.1 source is folded to 5.1, which every player decodes; stereo sources stay stereo);
- at 48 kHz at most: a track above 48 kHz is re-encoded for that reason alone
(
audio_samplerate_exceeded); at or below 48 kHz the sample rate is not a reason.
A copied track inside a transcoded or remuxed stream must also be a format the player accepts inside the stream's segments. AAC, AC-3 and E-AC-3 always are; other codecs only when the player says so. When it is not the case, the track is re-encoded and Stream info says Audio track cannot be passed through unchanged in the stream: a player may decode MP3 in a file and still refuse it inside a stream.
Dolby Digital in a browser¶
Most browsers cannot decode AC-3 or E-AC-3. Instead of re-encoding the track on the server, the web player decodes it itself, with a decoder that runs in the page: the track is sent unchanged and Stream info shows it as client-decoded. Browsers that decode Dolby Digital natively, such as Safari, receive it as an ordinary track; the choice is made by testing the browser, not by recognising it. A surround track is decoded in the page only when the profile's Max Audio Channels allows it: a profile set to stereo gets the AAC re-encode instead, which can fold the channels.
How the page decodes it, and what happens when it cannot: ac3go in Evey.
Warning
A reverse proxy that sets its own Content-Security-Policy must allow
'wasm-unsafe-eval' in script-src, otherwise the decoder cannot start
and the film plays without sound. See
Reverse proxy configurations.
Sound out of sync¶
Audio sync in the player shifts the sound for the current title (positive values play it later). It is offered when the stream comes from the server as a remux or a transcode; in Direct Play the control reads Available during transcoded playback only. Applying a shift restarts the stream at the current position. A copied track cannot be shifted, so the server re-encodes it and Stream info shows Audio resync requested.
When the offset is in the file itself (an audio track that starts after the picture, or tracks that disagree with each other), Admin → Media Health reports it but never rewrites it on its own: an offset that starts late is usually a deliberate dub alignment. Check sync on the file's row lets you judge it by eye and apply a shift, which its history can undo. See Media health.