Histogram variance of an image

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Histogram variance of an image

Mar Andrés López
Dear All,


I would like to extract the first frame of a video that contains some 'information', I do not want just one color frames (White,red, black…).


In order to achieve that the histogram variance calculation of an image could be a Good starting point. I would like that the variance is low so I guess I would have an image from the video with low difference between its pixels.

(Not al pixels White).


Is that posible to achieve that with ffmpeg or ffprobe?, what I found at the moment is that i can print the histogram with:


ffplay -i input -vf histogram

A lot of thanks,

P Please consider the environment before printing this e-mail.
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Zero or omit timecode in DV to mp4

Matti Haveri
How to zero or omit timecode in DV to mp4?

ffmpeg by default copies timecode from .dv to H.265 .mp4. My .dv files
start at random timecodes like 00:25:06:16 I don't need and I'd like
to either zero them to 00:00:00:00 or maybe omit them when converting
to .mp4.

It seems it is possible to zero them with:

for i in *.dv; do ffmpeg -i "$i" -vf
bwdif=1,scale=788:576,crop=768:576:10:0,setsar=sar=1/1 -c:v libx265 -crf 18
-preset slow -timecode 00:00:00:00 -tag:v hvc1 -c:a aac -b:a 128k
"${i%.*}_converted.mp4"; done

Does it matter where the '-timecode' option is? With other libx265
options or after video and audio options?

Some sources say that timecode_rate option must be specified with
something like '-timecode 00:00:00:00:r=50' but that does not seem to
make any difference. Is it meant for burning the timecode in (with
some added options)?

With the command above in the Terminal output there is '0.02 fps'.
What does it mean?

Stream #0:0: Video: hevc (libx265) (hvc1 / 0x31637668), yuv420p, 768x576
[SAR 1:1 DAR 4:3], q=-1--1, 0.02 fps, 12800 tbn, 50 tbc

On the other hand, if instead '-timecode 00:00:00:00' I omit timecode
with '-write_tmcd off' the output has a more reasonable '50 fps':

Stream #0:0: Video: hevc (libx265) (hvc1 / 0x31637668), yuv420p, 768x576
[SAR 1:1 DAR 4:3], q=-1--1, 50 fps, 12800 tbn, 50 tbc

Is that just a cosmetic issue or should I fine-tune the command?

- Matti
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