[FFmpeg-user] Question about tmix filter

Paul B Mahol onemda at gmail.com
Wed Mar 6 22:53:25 EET 2019

On 3/6/19, Michael Koch <astroelectronic at t-online.de> wrote:
> Am 06.03.2019 um 20:45 schrieb Paul B Mahol:
>>>>> Your interpretation of test results is invalid.
>>>>> You should count frames.
>>>> Well, I did run the video in VLC and measure the duration with a
>>>> stopwatch, and it is 5 seconds. Below is the FFprobe output.
>>>> How can I count the frames?
>>> Old fashioned way - by hand.
>> -f null -
>> AKA null muxer counts frames for you.
> ok, it's 76 frames and 5 seconds. Lesson learned, don't trust the video
> length.
> Next question. I want to make a dark subtract for my videos of the night
> sky. I capture a few seconds of video with the cap on the lens. From
> this video I want to average 100 frames and extract the result as a PNG
> image, which will then be subtracted from the video of the night sky.
> Do you think this is the correct command for extracting the average of
> the first 100 frames?
> ffmpeg -i dark.mov -vf tmix=frames=100 -frames 1 dark.png

Only first frame will be average of first 100 frames.

> Thanks,
> Michael
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