[FFmpeg-devel] [PATCH] af_volume: fix integer clip

[Michael Niedermayer]

On Sat, Feb 01, 2020 at 06:06:39PM +0800, zhilizhao wrote:
> 
> 
> > On Jan 27, 2020, at 6:28 PM, Zhao Zhili <quinkblack at foxmail.com> wrote:
> > 
> > 
> > 
> >> On Jan 27, 2020, at 12:59 AM, Carl Eugen Hoyos <ceffmpeg at gmail.com <mailto:ceffmpeg at gmail.com>> wrote:
> >> 
> >> Am So., 26. Jan. 2020 um 17:13 Uhr schrieb Zhao Zhili <quinkblack at foxmail.com <mailto:quinkblack at foxmail.com>>:
> >>> 
> >>> ---
> >>> Or specify an upper limit on volume. What do you think?
> >>> 
> >>> libavfilter/af_volume.c | 2 +-
> >>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>> 
> >>> diff --git a/libavfilter/af_volume.c b/libavfilter/af_volume.c
> >>> index 213c57195a..029925cbfb 100644
> >>> --- a/libavfilter/af_volume.c
> >>> +++ b/libavfilter/af_volume.c
> >>> @@ -200,7 +200,7 @@ static inline void scale_samples_s16(uint8_t *dst, const uint8_t *src,
> >>>     int16_t *smp_dst       = (int16_t *)dst;
> >>>     const int16_t *smp_src = (const int16_t *)src;
> >>>     for (i = 0; i < nb_samples; i++)
> >>> -        smp_dst[i] = av_clip_int16(((int64_t)smp_src[i] * volume + 128) >> 8);
> >>> +        smp_dst[i] = (int16_t)av_clip64(((int64_t)smp_src[i] * volume + 128) >> 8, INT16_MIN, INT16_MAX);
> >> 
> >> The cast looks unnecessary and confusing but if a limit works, it is likely
> >> simpler imo.
> > 
> > The function is supposed to handle smp_src[i] * volume > INT32_MAX, so the cast is necessary.
> > 
> >     case AV_SAMPLE_FMT_S16:
> >         if (vol->volume_i < 0x10000)
> >             vol->scale_samples = scale_samples_s16_small;
> >         else
> >             vol->scale_samples = scale_samples_s16;
> >         break;
> > 
> > I'm not sure about the use case. Does the function suppose to handle
> > (((int64_t)smp_src[i] * volume + 128) >> 8) > INT32_MAX?
> > 
> > By the way, there is another overflow in set_volume():
> > 
> >     if (vol->precision == PRECISION_FIXED) {
> >         vol->volume_i = (int)(vol->volume * 256 + 0.5);
> >         vol->volume   = vol->volume_i / 256.0;
> >         av_log(ctx, AV_LOG_VERBOSE, "volume_i:%d/255 ", vol->volume_i);
> >     }
> 
> Ping. Any suggestions?

no but a question
for the 64bit clip to make a difference the volume needs to be increased by
like a factor of 65536. so everything will clip. Does this have a usecase ?
or maybe iam missing something ?

Thanks

[...]

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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