[FFmpeg-devel] [PATCH] libswresample: avoid s16p internal processing format

[Paul B Mahol]

On 1/9/23, Tobias Rapp <t.rapp at noa-archive.com> wrote:
> On 08/01/2023 15:45, Michael Niedermayer wrote:
>
>> On Fri, Jan 06, 2023 at 07:01:06PM +0100, Paul B Mahol wrote:
>>> On Fri, Jan 6, 2023 at 6:25 PM Michael Niedermayer
>>> <michael at niedermayer.cc>
>>> wrote:
>>>
>>>> On Thu, Jan 05, 2023 at 11:08:25PM +0100, Paul B Mahol wrote:
>>>>> On Thu, Jan 5, 2023 at 9:53 PM Michael Niedermayer <
>>>> michael at niedermayer.cc>
>>>>> wrote:
>>>>>
>>>>>> On Thu, Jan 05, 2023 at 01:44:10PM +0100, Paul B Mahol wrote:
>>>>>>> Patch attached.
>>>>>>>   swresample.c |    3 ++-
>>>>>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>>> eee7a0685b44aa867562138a2e2437ecb8844612
>>>>>> 0001-libswresample-swresample-avoid-s16p-internal-transfe.patch
>>>>>>>  From 9c4cd60e2dd41cf98d693c8251f4cfade0807073 Mon Sep 17 00:00:00
>>>> 2001
>>>>>>> From: Paul B Mahol <onemda at gmail.com>
>>>>>>> Date: Thu, 5 Jan 2023 13:40:12 +0100
>>>>>>> Subject: [PATCH] libswresample/swresample: avoid s16p internal
>>>> transfer
>>>>>> format
>>>>>>> Instead use float one by default for sample rate conversions.
>>>>>>> The s16p internal transfer format produces visible and hearable
>>>>>>> quantization artifacts.
>>>>>> When does this occur and why?
>>>>>>
>>>>> It occurs always. Just compare output with 16bit and
>>>>> int32/float/double.
>>>>> Look at other people report on internet.
>>>>> Look at src.infinitewave.ca
>>>> src.infinitewave.ca uses 32bit none of what it shows should touch the
>>>> codepath
>>>> you change.
>>>>
>>>> if we look at src.infinitewave.ca for swr we see 2 types of artifacts
>>>> 1. Aliassing which is at maybe -120db with the actual signal at 0db
>>>>     i would like to see some evidence that a human can hear this
>>>>
>>> For s16p<->s16p it is much lower, around -78dB thus this patch.
>> ok but you pointed to the website that apparently uses >=32bit if i trust
>> what they write.
>> And even if they test this i cannot use that website to replicate the
>> issue
>> and the fix
>>
>> I just wanted to know how i can test this. You are testing it too ...
>> so i can see what you see
>> Id like to make sure this is the correct fix for the problem and
>> Id like to make sure its used when it makes sense and not when not.
>
> IIRC a similar sweep graph can be created with "Spek" from
> http://spek.cc/ but haven't used that application for a while. The SRC

Spek is both slow and limited in range of dB, so it should never be
used by pro users.

> comparison website apparently provides the input files for testing, see
> the instructions at http://src.infinitewave.ca/faq.html.
>
> Regards, Tobias
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