[FFmpeg-user] Question about tmix filter

[Michael Koch]

Am 06.03.2019 um 21:53 schrieb Paul B Mahol:
> 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.

Yes of course. I need only one png image for dark subtract.

Michael