aptX LL support

[ehfive]

aptX LL support

[ValdikSS]

I've quick-patched @EHfive's module to support aptX Low Latency and it worked with stock libopenaptx. I've got about 50-65 ms of latency, which is much lower than with stock aptX.
Mailed @pali and @EHfive the Bluetooth dump with aptX LL traffic.

[a-rasinski]

@EHfive Hey! Awesome work you did with this pa module.
Would really love to have aptx-ll supported. What's the main issue with implementing this? If it's just some tedious work maybe I could help with little guidance from your side. I've been able to build the project and successfully get it running and able to test. Also I have aptx-ll compat device.

[noygal]

@EHfive Thanks for the great work!

Sadly aptx-ll is 'forgotten' on many audiophile devices due to its lower sound quality and licence structure of codex family. The codex has a real value to htpc/gaming setups, where you can place raspberry pi (or other boards) that would receive the output sound from tv/receiver and broadcast it in the aptx-ll format. I have tried multiple BT solutions, built-in and externals, with multiple streaming codexes, none except aptx-ll offer the level of latency acceptable for video/gaming.

I would like to help out with this feature, but I'm a js developer myself with a past experience from around 10 year ago at C++ (real time image processing). If you can spare the time and have the will, please share some links on the specs/structure of the codex and what need to be done, so I (or someone else) could follow this up.

In any case it would be nice to reopen this issue and add help needed tag to it.

[EHfive]

pali/libopenaptx#1 (comment)

Seems aptX LL & aptX Classic share the encoding/decoding processes.

If someone can help to test, aptX LL support could be added to this module.(I have no aptX LL capable device)

[noygal]

I've quick-patched @EHfive's module to support aptX Low Latency and it worked with stock libopenaptx. I've got about 50-65 ms of latency, which is much lower than with stock aptX.
Mailed @pali and @EHfive the Bluetooth dump with aptX LL traffic.

@ValdikSS can you share your repository? I'll love to test this out.

[BAAZKonqi]

Hi, did the the aptX LL feature make it into the module?
Otherwise I'd really like to see your patched one. @ValdikSS

[morguldir]

I can help, i have aptx LL capable headphones, just tell me what to do.

[EHfive]

Thanks all.

When I look into aptx LL configuration headers, I found that aptX LL have 7 more parameters than aptX.
So let other one to test it would be inefficient,
I decide to put down it now.

typedef struct {
	uint8_t reserved;
	uint8_t target_level2;
	uint8_t target_level1;
	uint8_t initial_level2;
	uint8_t initial_level1;
	uint8_t sra_max_rate;
	uint8_t sra_avg_time;
	uint8_t good_working_level2;
	uint8_t good_working_level1;
} __attribute__ ((packed)) a2dp_aptx_ll_new_caps_t;

typedef struct {
	a2dp_vendor_codec_t info;
	uint8_t channel_mode:4;
	uint8_t frequency:4;
} __attribute__ ((packed)) a2dp_aptx_t;

typedef struct {
	a2dp_vendor_codec_t info;
	uint8_t direction;
	uint8_t sink_frequency:4;
	uint8_t source_frequency:4;
} __attribute__ ((packed)) a2dp_faststream_t;

typedef struct {
	a2dp_vendor_codec_t info;
	uint8_t channel_mode:4;
	uint8_t frequency:4;
	uint8_t bidirect_link:1;
	uint8_t has_new_caps:1;
	uint8_t reserved:6;
	a2dp_aptx_ll_new_caps_t new_caps[0];
} __attribute__ ((packed)) a2dp_aptx_ll_t;

[odensc]

@BAAZKonqi nope, but there is a patch for it upstream (I haven't personally tested it)

Edit: Actually it might not be there yet... the author said they planned on it. (see #100)