by Frédéric DALLEAU

[permalink] [raw]

Subject: [PATCH 2/5] Add support for mSBC frame header

mSBC modifies header so that it contains: OxAD 0x00 0x00.
The first bytes allows to distinguish mSBC packets from standard SBC
packets used in A2DP. The two zero bytes are reserved for future definition.
---
sbc/sbc.c | 104 +++++++++++++++++++++++++++++++++++++------------------------
1 file changed, 63 insertions(+), 41 deletions(-)

diff --git a/sbc/sbc.c b/sbc/sbc.c
index 7e4faa0..131755b 100644
--- a/sbc/sbc.c
+++ b/sbc/sbc.c
@@ -407,55 +407,71 @@ static int sbc_unpack_frame(sbc_t *sbc, const uint8_t *data,
if (len < 4)
return -1;

- if (data[0] != SBC_SYNCWORD)
- return -2;
-
- frame->frequency = (data[1] >> 6) & 0x03;
+ if (sbc->flags & SBC_MSBC) {
+ if (data[0] != MSBC_SYNCWORD)
+ return -2;
+ if (data[1] != 0)
+ return -5;
+ if (data[2] != 0)
+ return -6;

- frame->block_mode = (data[1] >> 4) & 0x03;
- switch (frame->block_mode) {
- case SBC_BLK_4:
- frame->blocks = 4;
- break;
- case SBC_BLK_8:
- frame->blocks = 8;
- break;
- case SBC_BLK_12:
- frame->blocks = 12;
- break;
- case SBC_BLK_16:
- frame->blocks = 16;
- break;
- }
- if (sbc->flags & SBC_MSBC)
+ frame->frequency = SBC_FREQ_16000;
+ frame->block_mode = SBC_BLK_4;
frame->blocks = MSBC_BLOCKS;
-
- frame->mode = (data[1] >> 2) & 0x03;
- switch (frame->mode) {
- case MONO:
+ frame->allocation = LOUDNESS;
+ frame->mode = MONO;
frame->channels = 1;
- break;
- case DUAL_CHANNEL: /* fall-through */
- case STEREO:
- case JOINT_STEREO:
- frame->channels = 2;
- break;
- }
+ frame->subband_mode = 1;
+ frame->subbands = 8;
+ frame->bitpool = 26;
+ } else {
+ if (data[0] != SBC_SYNCWORD)
+ return -2;
+
+ frame->frequency = (data[1] >> 6) & 0x03;
+ frame->block_mode = (data[1] >> 4) & 0x03;
+ switch (frame->block_mode) {
+ case SBC_BLK_4:
+ frame->blocks = 4;
+ break;
+ case SBC_BLK_8:
+ frame->blocks = 8;
+ break;
+ case SBC_BLK_12:
+ frame->blocks = 12;
+ break;
+ case SBC_BLK_16:
+ frame->blocks = 16;
+ break;
+ }
+
+ frame->mode = (data[1] >> 2) & 0x03;
+ switch (frame->mode) {
+ case MONO:
+ frame->channels = 1;
+ break;
+ case DUAL_CHANNEL: /* fall-through */
+ case STEREO:
+ case JOINT_STEREO:
+ frame->channels = 2;
+ break;
+ }

- frame->allocation = (data[1] >> 1) & 0x01;
+ frame->allocation = (data[1] >> 1) & 0x01;

- frame->subband_mode = (data[1] & 0x01);
- frame->subbands = frame->subband_mode ? 8 : 4;
+ frame->subband_mode = (data[1] & 0x01);
+ frame->subbands = frame->subband_mode ? 8 : 4;

- frame->bitpool = data[2];
+ frame->bitpool = data[2];

- if ((frame->mode == MONO || frame->mode == DUAL_CHANNEL) &&
- frame->bitpool > 16 * frame->subbands)
- return -4;
+ if ((frame->mode == MONO || frame->mode == DUAL_CHANNEL) &&
+ frame->bitpool > 16 * frame->subbands)
+ return -4;

- if ((frame->mode == STEREO || frame->mode == JOINT_STEREO) &&
- frame->bitpool > 32 * frame->subbands)
- return -4;
+ if ((frame->mode == STEREO || frame->mode == JOINT_STEREO) &&
+ frame->bitpool > 32 * frame->subbands)
+ return -4;
+ }

/* data[3] is crc, we're checking it later */

@@ -800,6 +816,11 @@ static SBC_ALWAYS_INLINE ssize_t sbc_pack_frame_internal(sbc_t *sbc,
uint32_t levels[2][8]; /* levels are derived from that */
uint32_t sb_sample_delta[2][8];

+ if (sbc->flags & SBC_MSBC) {
+ data[0] = MSBC_SYNCWORD;
+ data[1] = 0;
+ data[2] = 0;
+ } else {
data[0] = SBC_SYNCWORD;

data[1] = (frame->frequency & 0x03) << 6;
@@ -831,6 +852,7 @@ static SBC_ALWAYS_INLINE ssize_t sbc_pack_frame_internal(sbc_t *sbc,
if ((frame->mode == STEREO || frame->mode == JOINT_STEREO) &&
frame->bitpool > frame_subbands << 5)
return -5;
+ }

/* Can't fill in crc yet */

--
1.7.9.5

2012-10-30 02:18:50

by Siarhei Siamashka

[permalink] [raw]

Subject: Re: [PATCH 0/5] mSBC tests

On Fri, 28 Sep 2012 17:05:42 +0200
Marcel Holtmann <[email protected]> wrote:

> > > Work done from the spec, not tested with any reference encoder.
> >
> > Does a reference mSBC encoder exist somewhere? Or any ideas how to test
> > the new code with something other than bluez just to be sure that it's
> > correct?
>
> I looked at the Bluetooth SIG website and couldn't find a reference
> encoder or sample files. The old SBC reference encoder and decoder don't
> seem to support other block sizes.
>
> SBC Encoder LIB Version 1.5
> Copyright (c) 2002 Philips Consumer Electronics, ASA Labs
>
> Usage:
> sbc_encoder [-jsv] [-lblk_len] [-nsubbands] [-p] [-rrate] [-ooutputfile] inputfile
> [-s] use the stereo mode for stereo signals
> [-v] verbose mode
> [-j] allow the use of joint coding for stereo signals
> [-lblk_len] blk_len specifies the APCM block length, out of [4,8,12,16]
> [-nsubbands] subbands specifies the number of subbands, out of [4,8]
> [-p] a simple psycho acoustic model is used
> [-rrate] specifies the bit rate in bps
> [-ooutputfile] specifies the name of the bitstream output file
> inputfile specifies the audio input file, the major audio formats are supported
>
>
> SBC Decoder LIB Version 1.5
> Copyright (c) 2002 Philips Consumer Electronics, ASA Labs
>
> Usage:
> sbc_decoder [-v] [-ooutputfile] [-pstartpos] inputfile
> [-v] verbose mode
> [-pstartpos] startpos specifies the byte offset to start with decoding
> [-ooutputfile] specifies the name of the audio output file
> inputfile specifies the name of the bitstream input file
>
> And the sample files are all from 2001. We might have to create our own
> ones and our own naive and stupid reference encoder/decoder.

Hi Marcel,

As the first step, some sort of automated testing ("make check") for
verifying sbc encoding/decoding correctness might be useful.

So far I have been using the following quickly hacked script. It just
takes a directory with *.au files, encodes them using different
settings and provides a log with md5 hashes which can be compared with
the reference log:

#!/usr/bin/env ruby

testfiles = []
Dir.new("testsamples").each {|file|
next if not file =~ /\.au$/
testfiles.push("testsamples/" + file)
}

if File.exists?("sbc-test.ok") then
fh = File.open("sbc-test.ok", "r")
okdata = fh.read()
fh.close()
end

outstring = ""

testfiles.sort!

testfiles.each {|file|

["-b32", "-b64", "-b128", "-b255"].each {|br|
["-s4", "-s8"].each {|sb|
["-S", ""].each {|snr|
["-j", ""].each {|j|
["-d", ""].each {|d|
["-B4", "-B8", "-B12", "-B16"].each {|blk|
outstring += sprintf("%s #{file} (#{br} #{sb} #{snr} #{j} #{d} #{blk})\n",
`./sbcenc #{br} #{sb} #{snr} #{j} #{d} #{blk} #{file} 2>/dev/null | md5sum`.strip).gsub(/[ ]+/, " ")
}
}
}
}
}
}
}

if not okdata then
printf("no reference ok data\n")
end

if outstring != okdata then
printf("test failed!\n")
else
printf("test ok\n")
end

fh = File.open("sbc-test.results", "w")
fh.write(outstring)
fh.close()

############################

Though I see this scripts as a dead end, because my media files are a
bit too large for adding to a git repository and these files are
all copyrighted. Some of them have a permissive license (big buck
bunny soundtrack), some of them do not.

Anyway, based on the fact that we use a fixed point encoder for sbc and
its output is deterministic, we can just encode some pseudo random noise
data and compare the checksums/hashes of the encoded results with some
reference values.

--
Best regards,
Siarhei Siamashka