[opus] Issue with decoding 8-bit PCM data

[Amit Ashara]

Hello Benjamin,

The original WAV file I have is linear 8-bit PCM. I want to ensure that
original linear formats are kept as is.

Later I will add support for ulaw.

Regards
Amit

On Fri, Jan 8, 2016 at 5:34 PM, Benjamin Schwartz <
benjamin.m.schwartz at gmail.com> wrote:

> Do you really need linear 8-bit PCM or do you want ulaw?  Linear 8-bit is
> ... pretty rare.
>
> On Thu, Jan 7, 2016 at 8:11 PM, Amit Ashara <ashara.amit at gmail.com> wrote:
>
>> Hello Ralph,
>>
>> I was finally able to get it to work for both 8 and 16 bit PCM data.
>> However the output of the decoder is always 16 bit PCM and never the
>> original 8 bit making the wav file decoded 2x times the original file.
>>
>> This is a restriction for some embedded system. Any idea how to work
>> around or fix the issue?
>>
>> I did try reading out the 8-bit data from the 16 bit output but it does
>> not seem that simple (based on stackoverflow.com) and I am still
>> searching on an easier mechanism.
>>
>> Regards
>> Amit
>>
>> On Thu, Jan 7, 2016 at 12:41 PM, Amit Ashara <ashara.amit at gmail.com>
>> wrote:
>>
>>> Hello Ralph,
>>>
>>> > Likewise opus_encode() takes 16 bit samples, so you need to extend each
>>> > sample from an 8 bit source before encoding.
>>>
>>> Two questions
>>> 1. In opusenc.c which API does the extending the 8-bit to 16-bit?
>>> 2. If that is the case then how will 24 bit PCM sample work?
>>>
>>> Regards
>>> Amit
>>>
>>> On Thu, Jan 7, 2016 at 12:21 PM, Ralph Giles <giles at thaumas.net> wrote:
>>>
>>>> On 07/01/16 10:04 AM, Amit Ashara wrote:
>>>>
>>>> > opus_decoder_ctl(sOpusDec, OPUS_SET_LSB_DEPTH(ui32BitsPerSample));
>>>>
>>>> OPUS_SET_LSB_DEPTH only affects the encoder. If you check the return
>>>> value here you should get OPUS_UNIMPLEMENTED.
>>>>
>>>> > output_samples = opus_decode(sOpusDec, (const unsigned char
>>>> > *)&pcRdBuf[0], len, opi16_out, (ui32SizeOfWrBuf/ui8ScaleFactor), 0);
>>>>
>>>> I suspect the issue is dividing by ui8ScaleFactor = 1 here.
>>>> OPUS_SET_LSB_DEPTH works as a precision hint to the encoder about where
>>>> to set the noise floor, but opus_decode still returns 16 bit samples. It
>>>> always returns 16 bit samples, regardless of whether the original input
>>>> as 8 bit, 16 bit or 24 bit precision (from opus_encode_float).
>>>>
>>>> To actually output 8-bit wav, you have to keep track of this out-of-band
>>>> and truncate each sample before writing it out.
>>>>
>>>> Likewise opus_encode() takes 16 bit samples, so you need to extend each
>>>> sample from an 8 bit source before encoding.
>>>>
>>>> HTH,
>>>>  -r
>>>>
>>>
>>>
>>
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>> http://lists.xiph.org/mailman/listinfo/opus
>>
>>
>
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