[pulseaudio-discuss] [PATCH v13 05/10] bluetooth: Add A2DP aptX and aptX HD codecs support

[Pali Rohár]

On Thursday 12 December 2019 22:27:39 Andrey Semashev wrote:
> On 2019-10-06 20:58, Pali Rohár wrote:
> > This patch provides support for aptX and aptX HD codecs in bluetooth A2DP
> > profile. It uses open source LGPLv2.1+ licensed libopenaptx library which
> > can be found at https://github.com/pali/libopenaptx.
> > 
> > aptX for s24 stereo samples provides fixed 6:1 compression ratio and
> > bitrate 352.8 kbit/s, aptX HD provides fixed 4:1 compression ratio and
> > bitrate 529.2 kbit/s.
> > 
> > According to soundexpert research, aptX codec used in bluetooth A2DP is no
> > better than SBC High Quality settings. And you cannot hear difference
> > between aptX and SBC High Quality, aptX is just a copper-less overpriced
> > audio cable.
> > 
> > aptX HD is high-bitrate version of aptX. It has clearly noticeable increase
> > in sound quality (not dramatic though taking into account the increase in
> > bitrate).
> > 
> > http://soundexpert.org/news/-/blogs/audio-quality-of-bluetooth-aptx
> > ---
> >   configure.ac                            |  36 +++
> >   src/Makefile.am                         |   6 +
> >   src/modules/bluetooth/a2dp-codec-aptx.c | 479 ++++++++++++++++++++++++++++++++
> >   src/modules/bluetooth/a2dp-codec-util.c |   8 +
> >   4 files changed, 529 insertions(+)
> >   create mode 100644 src/modules/bluetooth/a2dp-codec-aptx.c
> 
> [snip]
> 
> > +
> > +static size_t encode_buffer(void *codec_info, uint32_t timestamp, const uint8_t *input_buffer, size_t input_size, uint8_t *output_buffer, size_t output_size, size_t *processed) {
> > +    struct aptx_context *aptx_c = (struct aptx_context *) codec_info;
> > +    size_t written;
> > +
> > +    *processed = aptx_encode(aptx_c, input_buffer, input_size, output_buffer, output_size, &written);
> > +    if (PA_UNLIKELY(*processed == 0 || *processed != input_size))
> > +        pa_log_error("aptX encoding error");
> > +
> > +    return written;
> > +}
> > +
> > +static size_t encode_buffer_hd(void *codec_info, uint32_t timestamp, const uint8_t *input_buffer, size_t input_size, uint8_t *output_buffer, size_t output_size, size_t *processed) {
> > +    struct aptx_hd_info *aptx_hd_info = (struct aptx_hd_info *) codec_info;
> > +    struct rtp_header *header;
> > +    size_t written;
> > +
> > +    if (PA_UNLIKELY(output_size < sizeof(*header))) {
> > +        *processed = 0;
> > +        return 0;
> > +    }
> > +
> > +    written = encode_buffer(aptx_hd_info->aptx_c, timestamp, input_buffer, input_size, output_buffer + sizeof(*header), output_size - sizeof(*header), processed);
> > +
> > +    if (PA_LIKELY(written > 0)) {
> > +        header = (struct rtp_header *) output_buffer;
> 
> I'm not sure I understand it correctly, but encode_buffer seems to be
> producing encoded content at the beginning of the output buffer, and
> encode_buffer_hd produces an RTP header followed by encoded content. Is this
> difference intentional? What is expected to be placed in the output buffer -
> a complete RTP packet or RTP payload only?
> 
> The same comment applies to decode_buffer and decode_buffer_hd below.

aptX does not use RTP. So A2DP buffer for aptX contains raw aptX
samples.

On the other hand aptX-HD uses RTP protocol, so aptX-HD samples are put
into RTP packets and then RTP packets are passed to A2DP buffer.

Hope this answer your question.

-- 
Pali Rohár
pali.rohar at gmail.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <https://lists.freedesktop.org/archives/pulseaudio-discuss/attachments/20191212/77cc2bcb/attachment.sig>