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.
+ pa_zero(*header);
+ header->v = 2;
+ header->pt = 96;
+ header->sequence_number = htons(aptx_hd_info->seq_num++);
+ header->timestamp = htonl(timestamp);
+ header->ssrc = htonl(1);
+ written += sizeof(*header);
+ }
+
+ return written;
+}
+
+static size_t decode_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_decode(aptx_c, input_buffer, input_size, output_buffer, output_size, &written);
+
+ /* Due to aptX latency, aptx_decode starts filling output buffer after 90 input samples.
+ * If input buffer contains less than 90 samples, aptx_decode returns zero (=no output)
+ * but set *processed to non zero as input samples were processed. So do not check for
+ * return value of aptx_decode, zero is valid. Decoding error is indicating by fact that
+ * not all input samples were processed. */
+ if (PA_UNLIKELY(*processed != input_size))
+ pa_log_error("aptX decoding error");
+
+ return written;
+}
+
+static size_t decode_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(input_size < sizeof(*header))) {
+ *processed = 0;
+ return 0;
+ }
+
+ header = (struct rtp_header *) input_buffer;
+ written = decode_buffer(aptx_hd_info->aptx_c, timestamp, input_buffer + sizeof(*header), input_size - sizeof(*header), output_buffer, output_size, processed);
+ *timestamp = ntohl(header->timestamp);
+ *processed += sizeof(*header);
+ return written;
+}
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