[FFmpeg-devel] [PATCH] swresample/swresample: do not use s32p internally by default when resampling

[Muhammad Faiz]

On Thu, Mar 16, 2017 at 1:01 PM, wm4 <nfxjfg at googlemail.com> wrote:
> On Thu, 16 Mar 2017 12:43:10 +0700
> Muhammad Faiz <mfcc64 at gmail.com> wrote:
>
>> use fltp when doing s32 -> s32 resampling
>> because s32p has no simd optimization
>>
>> benchmark:
>> old 17.913s
>> new  7.584s (use fma3)
>>
>> Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
>> ---
>>  libswresample/swresample.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/libswresample/swresample.c b/libswresample/swresample.c
>> index f2e6600..74c96dc 100644
>> --- a/libswresample/swresample.c
>> +++ b/libswresample/swresample.c
>> @@ -223,6 +223,8 @@ av_cold int swr_init(struct SwrContext *s){
>>          }else if(   av_get_planar_sample_fmt(s-> in_sample_fmt) == AV_SAMPLE_FMT_S32P
>>                   && av_get_planar_sample_fmt(s->out_sample_fmt) == AV_SAMPLE_FMT_S32P
>>                   && !s->rematrix
>> +                 && s->out_sample_rate == s->in_sample_rate
>> +                 && !(s->flags & SWR_FLAG_RESAMPLE)
>>                   && s->engine != SWR_ENGINE_SOXR){
>>              s->int_sample_fmt= AV_SAMPLE_FMT_S32P;
>>          }else if(av_get_bytes_per_sample(s->in_sample_fmt) <= 4){
>
> Wouldn't going over float lose bits?

Yes, of course. But when resampling with default opt, aliasing happens at
about -90dB which is only 15 bits. Keeping 32 bits has no point at all.

> I guess most times, s32 is
> actually 24 bit padded (since we have no 24 bit format). But it could
> be true 32 bit as well (with all bits used). Or does it use double, or
> am I missing something else?

Using double is overkill, i think.