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

[zhilizhao]

> 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?

> 
>> 
>> Carl Eugen
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