[FFmpeg-user] -threads 1 seems not work

[Paul B Mahol]

On 9/12/22, Cecil Westerhof via ffmpeg-user <ffmpeg-user at ffmpeg.org> wrote:
> Paul B Mahol <onemda at gmail.com> writes:
>
>> On 9/12/22, Cecil Westerhof via ffmpeg-user <ffmpeg-user at ffmpeg.org>
>> wrote:
>>> Paul B Mahol <onemda at gmail.com> writes:
>>>
>>>> On 9/12/22, Cecil Westerhof via ffmpeg-user <ffmpeg-user at ffmpeg.org>
>>>> wrote:
>>>>> For a certain conversion I use '-threads 1'. As I understand it ffmpeg
>>>>> should then only use one CPU. I see that the CPU usage is lower as
>>>>> without this parameter, but it goes up to 180%. So clearly it is using
>>>>> at least two CPU's.
>>>>> Or am I understanding this parameter wrongly?
>>>>>
>>>>> I am using ffmpeg version 4.3.4-0+deb11u1. (Debian always lags a
>>>>> little bit behind to be more stable.)
>>>>>
>>>>
>>>> threads can be used for input decoding, output encoding and filtering.
>>>>
>>>> You need to use threads = 1 for all 3 of them.
>>>
>>> I see:
>>>     -filter_threads
>>>     -filter_complex_threads
>>>
>>> But nothing for input decoding and output decoding.
>>>
>>>
>>> By the way: does this mean that ffmpeg can always use 4 CPU's?
>>> (input, output, filtering and complex filtering)
>>
>> No, ffmpeg may use sometimes only 1 or sometimes all available CPUs.
>> That depends on many factors.
>
> OK. But that  still means it can use  three CPU's if it wants  to if I
> have set all three to one?

For older versions you currently use that is not true.

>
>> -threads is both input and output option.
>
> --
> Cecil Westerhof
> Senior Software Engineer
> LinkedIn: http://www.linkedin.com/in/cecilwesterhof
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