Flac HD 192 KHz and multichannel

[Kumar Rounak]

I have been trying to port Flac HD (192Khz 24 bit) on android 4.2.2 but don't know how to proceed, I came across some change list in which you enabled multi channel flac on android.

Can someone give me some pointer on how to start also if possible on how to enable downsampling support in AudioFLinger.

Thanks,

Rounak

[Glenn Kasten]

The internal audio framework data path is currently mostly stereo 44.1 or 48 kHz and 16-bit depth, 

with notable exceptions for specific use cases (in particular multi-channel and HDMI).

If you wanted to add 192 kHz and 24-bit throughout the whole framework, that would be a significant project.

But as I understand you just want to convert your FLAC HD content to a form that rest of system can handle.

So I think you'll need to implement a 24-bit -> 16-bit dither, and a 192 -> 44.1 or 48 downsampler with lowpass filter to remove any high-frequency components.

As far as multi-channel, there is already a multi-channel to stereo virtualizer/downmixer effect so you shouldn't need to implement that.

[Kumar Rounak]

Thanks for your reply.

As you said:
If you wanted to add 192 kHz and 24-bit throughout the whole framework, that would be a significant project.

What it would take to do this?
We are having a 5.1 channel HD DAC which is connected to the system we want the decoded data to go to this DAC.

[Glenn Kasten]

In addition to the tasks listed in my 11/24 post, then you'll also need a new audio HAL (hardware abstraction layer) and may need to update the HAL interface.

I would start by studying the code in these projects, along with any of their dependencies (not a complete list):

frameworks/av/services/audioflinger

hardware/libhardware/include/*audio*

frameworks/media/libmedia/AudioTrack*

frameworks/av/include/media/*Audio*

system/media/audio_utils

frameworks/av/media/libeffects

system/core/include/system/audio.h

Again, I don't mean to discourage you, but this is a significant project.