Hi txp0wer,
Thanks for your input. This would work OK for the family of modes (say
1300 through 3200) that employ the same basic design.
However the latest modes like the 700 series and the new wideband work
are substantially different. They kind of have to be, as we are
breaking some new ground in order to inch towards my goals for the
project (competing with SSB on HF radio channels).
So I suggest a simple mode number, and let the software express all the
details.
Moving fwd, I'm also wondering about the relevance of many of the modes.
They evolved as a series of attempts to lower the bit rate and make the
codec more suitable for HF radio. However it doesn't cost much to keep
them available for backward compatibility, just two functions/mode in
codec2.c
Cheers,
David
On 25/07/17 02:35, txp0wer via Freetel-codec2 wrote:
> Hi folks!
>
>> That said, the notion of managing the different bitrates does present a
>> challenge. I therefore suggest any such encoded file have some "magic"
>> bytes at the beginning, even if this is something as simple as 0x43 0x32
>> ("C2"). I then propose the next byte be the mode ID as defined in
>> codec2.h. This would allow c2enc/c2dec to be retrofitted or separate
>> tools to be constructed to Do The Right Thing™ based on these.
>
> May I suggest a bitstream header format that encodes all the profile
> parameters, so that new profiles can be added without changing the
> header format or adding new "magic" numbers for profiles.
>
> 73 de txp0wer
>
>>
>> If we can agree on these bytes, I'm happy to take a stab at coding this
>> up. It doesn't look like it should be too difficult (famous last words!)
>>
>> 73 de Kevin N8VNR
>>
>> On 05/22/2017 04:35 PM, Kevin Otte wrote:
>>> Or Matroska (.mka):
>>> https://matroska.org/technical/specs/index.html
>>>
>>> On 05/22/2017 02:28 PM, Bruce Perens wrote:
>>>> See https://www.xiph.org/ogg/doc/rfc3533.txt . Make it work with the
>>>> Ogg Encapsulation Format.
>
> <code language="pseudocode" style="Rust">
> // data types:
> // u8 == unsigned 8-bit integer
> // u16b == unsigned 16-bit integer, big endian
>
> struct Codec2Header{
> magic_identification :u24b, // offset 0 bytes
> // const 0xC0DEC2 ([0xC0,0xDE,0xC2])
> major_version :u8, // offset 3 bytes //
> minor_version :u8, // offset 4 bytes //
> forward_ec_level :u8, // offset 6 bytes //
> flags :u8, // offset 5 bytes // default 0
> subframes_per_frame :u8, // offset 7 bytes // 1 to 4
> samples_per_subframe :u16b, // offset 8 bytes
> samplerate_hz :u16b // offset 10 // default 8000
> };
>
> struct Codec2SubframeParameters{ // offset 12
> // repeated [subframes_per_frame] times
> lsp_bits_per_frame :u8, // offset 12+4*n
> pitch_bits_per_frame :u8, // offset 12+4*n+(0..1)
> energy_bits_per_frame :u8, // offset 4*n+(0..1)
> voicing_bits_per_frame :u8 // offset 4*n+(0..1)
> }
>
> match forward_ec_level{
> 0=>none,
> 1=>"1200",
> 2=>"1850",
> 3=>"2000",
> _=>undefined
> }
>
> flags:
> 0x01=NATURAL_BYTE_ORDER // --natural
> 0x02=ALTERNATE_MODE_1 // "B"
> 0x04=ALTERNATE_MODE_2 // "C", "D"
> 0x08=ALTERNATE_MODE_4 // "E" .. "H"
> 0x10=unused
> 0x20=unused
> 0x40=unused
> 0x80=ALTERNATE_CODEBOOK_1
>
> </code>
>
> example (hex)
> # "3200" default profile
> # begin Codec2Header
> 00: C0 DE C2
> 03: 00 04 # version 0.4
> 05: 00 # no forward error correction
> 06: 00 # flags: gray code, no alternate profile, no alternate codebook
> 07: 02 # 2 subframes per frame
> 08: 00 a0 # 160 samples per subframe => 320 samples per frame
> 0a: 1f 40 # 8000 Hz
> # end Codec2Header, begin Codec2SubframeParameters
> # # begin subframe 0 # if I understand codec2_encode_3200() right
> 0c: 20 # 32 bits LSP
> 0d: 00 # 0 bits pitch
> 0e: 00 # 0 bits energy
> 0f: 00 # 0 bits voicing
> # # end subframe 0, begin subframe 1
> 10: 12 # 18 bits LSP
> 11: 07 # 0 bits pitch
> 12: 05 # 0 bits energy
> 13: 02 # 0 bits voicing
> # # end subframe 1
> # end Codec2SubframeParameters, begin data bitstream
>
>
>
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