[FFmpeg-user] curves filter and tmix filter, suggestions for improvement

Michael Koch astroelectronic at t-online.de
Sun Feb 3 19:38:15 EET 2019

Am 02.02.2019 um 19:34 schrieb Michael Koch:
> Am 02.02.2019 um 19:28 schrieb Paul B Mahol:
>> On 2/2/19, Michael Koch <astroelectronic at t-online.de> wrote:
>>> Am 02.02.2019 um 19:01 schrieb Paul B Mahol:
>>>> On 2/2/19, Michael Koch <astroelectronic at t-online.de> wrote:
>>>>> Hi all,
>>>>> I have two suggestions for improvement:
>>>>> 1. It would be nice if the curves filter could import curves files 
>>>>> from
>>>>> GIMP. GIMP can export curves files in two different formats, 
>>>>> either the
>>>>> default format or the "old curves file format". For the old format I
>>>>> have a selfmade C# converter to the *.acf format which FFmpeg's 
>>>>> curves
>>>>> filter can import. But it would be better if FFmpeg could directly
>>>>> import GIMP's newer curves format, because it contains more 
>>>>> informations.
>>>>> 2. For the tmix filter it would be nice if it would accept "frames 
>>>>> = 1",
>>>>> meaning "no mixing at all, just a bypass mode". Then it's easier to
>>>>> switch the filter on and off with a variable in batch file.
>>>>> Please add to the documentation: "If the weights parameter is not
>>>>> specified, the default is 1 for each frame".
>>>> This is not correct, default is one as described in documentation.
>>> The documentation doesn't even mention that it's possible to omit the
>>> weights parameter.
>>> But it is possible, and I'm quite sure that all default weights are 1.
>>> https://www.ffmpeg.org/ffmpeg-all.html#tmix
>> If you omit parameter you get default values....
> Yes, of course. But it's not written in the documentation that all 
> default weights are 1. It's an undocumented feature that you can omit 
> the weights parameter.

The last sentence in the tmix documentation is misleading:
"By default scale is auto scaled to sum of weights."
The reader might think the default value is the sum of weights. It would 
be better to write:
"By default scale is set to 1 / (sum of weights)."


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