> On 8 Apr 2021, at 10:23, Michael Koch <astroelectro...@t-online.de> wrote: > > Am 08.04.2021 um 09:46 schrieb Rainer M Krug: >> Hi >> >> I have a series of videos of moving particles (multiple particles per frame >> / movie), and would like to add a circle around each particle and add a >> label. At the moment I am using a script in R to plot, for each frame, these >> circles and labels into a png with alpha channel, combine the pngs to a >> movie, and overlay this movie to the original movie (see the thread 'Overlay >> images to frames in video’ for the background). >> >> Now I realised, that the actual plotting of the labels takes up nearly 40% >> of the time of the R script and I would like to make this process faster. >> >> I have found “draw_text” (https://ffmpeg.org/ffmpeg-filters.html#drawtext), >> but I have no idea how I could do this. We can assume that I have a text >> file with the following columns: >> >> FRAME: the frame on which the labels and circle should be plotted >> X: the x-coordinate >> Y: the y=coordinate >> LABEL: label for the point >> >> Also possibly important, there are multiple (many) particles for which >> circles and labels need to be plotted on each frame. >> >> I also found the “sendcmd” >> (https://ffmpeg.org/ffmpeg-filters.html#sendcmd_002c-asendcmd) but I do not >> get my head around how I can combine these two. > > It's possible to do this with FFmpeg if the number of particles is known in > advance
Yes it is > and constant in all frames. No it isn’t. But I should be able to extend the number of particles by plotting with size 0 or outside the frame? > Use several drawtext commands, one for each particle. So I would have for each particle and each frame, a draw text command in the command,txt file which is read using the sendcmd command - is this correct? Final point: how can I specify the frame as the start-end? I only fsaw in the documentation how to specify the time? > But with a changing number of particles I have no idea how to do it. There > are a few examples for sendcmd in chapter 2.86 of my book: > http://www.astro-electronic.de/FFmpeg_Book.pdf > <http://www.astro-electronic.de/FFmpeg_Book.pdf> Thanks for the link - I will loo into it, and it looks definitely useful! Rainer > > Michael > > _______________________________________________ > ffmpeg-user mailing list > ffmpeg-user@ffmpeg.org <mailto:ffmpeg-user@ffmpeg.org> > https://ffmpeg.org/mailman/listinfo/ffmpeg-user > <https://ffmpeg.org/mailman/listinfo/ffmpeg-user> > > To unsubscribe, visit link above, or email > ffmpeg-user-requ...@ffmpeg.org <mailto:ffmpeg-user-requ...@ffmpeg.org> with > subject "unsubscribe". -- Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys. (Germany) Orcid ID: 0000-0002-7490-0066 Department of Evolutionary Biology and Environmental Studies University of Zürich Office Y34-J-74 Winterthurerstrasse 190 8075 Zürich Switzerland Office: +41 (0)44 635 47 64 Cell: +41 (0)78 630 66 57 email: rainer.k...@uzh.ch rai...@krugs.de Skype: RMkrug PGP: 0x0F52F982
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