[opus] Issue with decoding 8-bit PCM data
ashara.amit at gmail.com
Thu Jan 14 14:43:34 PST 2016
Turned out to be a coding error. The modified buffer was not being
allocated to write back to the File System. After correction the mono 8 and
16 bit for 8K-48K works well now.
On Mon, Jan 11, 2016 at 11:05 AM, Amit Ashara <ashara.amit at gmail.com> wrote:
> Hello Mark,
> The resulting 8 bit file has a lot of squelching noise compared to the 16
> bit output from OPUS decoder.
> During encode I am using
> popi16fmtBuffer[ui32Loop] = (opus_int16)pcRdBuf[ui32Loop];
> And during decode since the data is in the lower 8 bit I use
> pc8bitSamples[ui32Loop] = ((unsigned short)pcop16OutBuf[ui32Loop] ^ 0x80);
> On Sat, Jan 9, 2016 at 2:39 PM, Amit Ashara <ashara.amit at gmail.com> wrote:
>> Hello Mark,
>> Thanks. Let me try the proposed configuration first to make sure that
>> linear 8-bit PCM is retrieved.
>> On Sat, Jan 9, 2016 at 12:28 PM, Mark Harris <mark.hsj at gmail.com> wrote:
>>> opus_decode() produces 16-bit signed linear PCM, and
>>> opus_decode_float() produces 32-bit floating point PCM that is useful
>>> when you want a higher bit depth.
>>> If you need 8-bit linear PCM then a simple solution would be to use
>>> only the top 8 bits of each 16-bit sample from opus_decode(). Note
>>> that the WAV format uses unsigned rather than signed integers for
>>> 8-bit linear PCM. (It uses signed for larger sample sizes and AIFF
>>> uses signed for all sizes.) So if you are writing 8-bit linear PCM to
>>> WAV then you would need something like (((unsigned short)sample ^
>>> 0x8000) >> 8) to convert from signed to unsigned and get the top 8
>>> bits of each sample.
>>> You will achieve better quality, however, if you apply dither.
>>> opusdec applies dither by default if the output is not floating point,
>>> although it does not support 8-bit output.
>>> - Mark
>>> opus mailing list
>>> opus at xiph.org
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