[FFmpeg-user] videodetect filter? - equivalent to:https://ffmpeg.org/ffmpeg-filters.html#silencedetect

[Mark Hassman]

> -----Original Message-----
> From: ffmpeg-user [mailto:ffmpeg-user-bounces at ffmpeg.org] On 
> Behalf Of Paul B Mahol
> Sent: Sunday, April 03, 2016 11:42 AM
> To: FFmpeg user questions
> Subject: Re: [FFmpeg-user] videodetect filter? - equivalent 
> to:https://ffmpeg.org/ffmpeg-filters.html#silencedetect
> 
> On 4/3/16, Moritz Barsnick <barsnick at gmx.net> wrote:
> > On Sat, Apr 02, 2016 at 17:02:19 -0400, Mark Hassman wrote:
> >> Any chance someone knows a set of filters to accomplish the same 
> >> thing for video as: 
> https://ffmpeg.org/ffmpeg-filters.html#silencedetect.. i.e.
> >> timestamps output for start/end of motion.
> >
> > While silence would be more like darkness in video ;-) I 
> get what you
> > mean:
> >
> >> I've looked at: 
> >> http://www.lavrsen.dk/foswiki/bin/view/Motion/WebHome, but already 
> >> transcoding with ffmpeg - hoping to add a simple filter to 
> accomplish the same.
> >
> > I too am looking for a filter which can at least imitate simple 
> > features of the tool "motion", as motion only does 
> real-time detection 
> > from input devices. This would mean replicating "motion"'s 
> algorithms 
> > in a filter, or using existing filters.
> >
> > I once tried, and had come to the conclusion - from reading 
> the docs - 
> > that the decimate filter might be close to the right thing. 
> While the 
> > docs mention "regular intervals", which wouldn't be 
> appropriate, they 
> > also speak of "threshold for duplicate detection" and "detection of 
> > [small] movements". I have never gotten the decimate filter to work 
> > for anything I needed it for though, which went beyond 
> motion detection.
> >
> > For anyone willing to help out, here are the main chaacteristics of 
> > "motion"'s features, some of which may not be feasible 
> within ffmpeg:
> > - Detection of motion by observing the number of changed pixels from
> >   one frame to the next, and passing this detected frame on to the
> >   output. (This could be a percentage or a mean square deviation
> >   instead, but "motion" doesn't support that.)
> > - Retaining a configurable amount of images before and after the
> >   detected event.
> > - Optionally visually marking the section of the video 
> where the change
> >   was detected. (This could be in frame metadata instead, 
> but "motion"
> >   doesn't support that.)
> >
> > At least the first point would be nice to have, but I'd rather not 
> > implement such a filter which reinvents the wheel.
> >
> > In other words: I too would appreciate a hint as how to use 
> ffmpeg's 
> > filters to achieve this.
> 
> See singnalstats filter.


Thanks for the advice!

Using signalstats YDIF, I'm able to derive what I need. However, I'm unable
to get the data out of ffmpeg for parsing/eventing.

The drawtext filter has access to all the set_meta values
(https://ffmpeg.org/pipermail/ffmpeg-cvslog/2014-June/078245.html) -
injecting the relevant data via graphical overlay works as expected, but I
can't find a way to push into stdout or ascii file.

Unsuccessfully, i've been looking for another filter capable of accessing
ffmpeg's internal meta tags to accomplish this. The closest i've found is
showinfo, but i can't specify which meta tags to use.

I've also tried the scene filter, but it modifies the video - i need only
reporting.

Note: I'm using ffmpeg - not ffprobe as this is a live encode.. ffmpeg
doesn't support -show_entries/frame_tags. Is there any way to effectively
reproduce this with ffmpeg?


Does anyone have ideas on this?
Thanks in advance!