Stereo downmix a TrueHD stream

Hey there

I am really happy that Infuse can play TrueHD streams through to my AVR. Unfortunately, due to the Apple TV design, the sound is output as PCM. According to the FAQ, there is no difference in the quality, since the PCM signal is “unpacked”.

I’ve recently learnt that the TrueHD stream contains a stereo track.

Does anyone know whether Infuse uses this information to send a Stereo signal? Can we force Infuse to output a stereo signal? If this is done on the Apple TV settings, then it’ll probably be downmixed on a platform level.


Infuse will do this automatically if/when required.

For example, if the Apple TV is connected to a TV (no AVR) you will get 2.0 stereo sound from a multi-channel audio track.


How is the stereo signal created? Is it downmixed or does it use the TrueHD metadata?

I have the Apple TV connected to the tv and the tv to an AVR. TV and avr support earc and 7.1

Yes, Infuse 7 will utilize the metadata elements embedded in audio tracks when passing audio from the app to the Apple TV hardware.

However, there are cases where the Apple TV can modify this. For example, if you have the Apple TV set to force Dolby 5.1 output, Infuse will still send send the full multi-channel output (EG 7.1) but the Apple TV will re-encode this on the fly to Dolby 5.1, which may change how things sound. Apple does not share the parameters they use when re-encoding to 5.1.

That’s awesome! Thanks James.

How can I force the Apple TV to output stereo using the metadata from TrueHD?

Relying on the AVR to downmix PCM isn’t as clear as using the Stereo track from a TrueHD stream.

You can force stereo output by adjusting the ‘Change Format’ option in Apple TV > Settings > Video and Audio > Audio Format.

And that would force Infuse to use the TrueHD metadata to create a stereo mix?

Yes, that’s correct.

Thanks that’s great.

According to your docs:

If audio is set to output in stereo then the stereo track wouldn’t be lossless since it’s downgraded from 24bit to 16bit?

Hmmm…that may be a typo. 2.0 is PCM, so still 24-bit.

Dolby (AC3) 5.1 is lossy and 16-bit.

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Nice. I’ll give it a go. I don’t think my avr has a way to display the bitrate of audio. Does infuse have an overlay that shows the current bitrate/resolution of the current video?

Infuse will always play things in the full native/original format, so we’ve not built an overlay to display the current quality. These overlays are mostly useful for streaming services where quality can vary depending on network conditions and other factors.

Thanks. In this case, is there anyway to confirm I’m playing a lossless 2.0 audio stream?

Unfortunately not.