Re: [FFmpeg-user] Output a sequence of images with known timings

[adam smith via ffmpeg-user]

> On 19 Nov 2020, at 10:42, Moritz Barsnick  wrote:
> 
> Do take a look at the documentation of the select filter. It even has
> an example on how to extract certain frames, e.g. by number:
> 
> https://ffmpeg.org/ffmpeg-filters.html#select_002c-aselect 
> 
> 
>Select one frame every 100:
>select='not(mod(n\,100))’


I have been playing with this filter to select frames but it to keep the frame 
rate of the source and hold the selected image.

For example If I was creating an mp4, it would have the first image held for 
ten seconds, then the image from 10 seconds held for ten seconds, then the 
image from 20 seconds etc. which is very useful for a video output to be fair ;)

When jpeg is selected, if the source was 25fps, I get a jpeg 250 of each 
selected frame.

When I used the tile filter in the following command it was able to show me all 
of the images I want combined into a single tile…
ffmpeg -y -i /data/temporary/localised_20201119-219-cniqnj/2minclock.m4v -vf 
select='not(mod(n\,1000))',scale=160:120,tile -frames:v 1 -pix_fmt yuvj420p 
-c:v mjpeg /data/temporary/transcode_20201119-219-kbzyx4/2minclockte
st_%03d.jpeg




Update:
I have tested with a large range of intervals and so far this looks to be 
working fine…
ffmpeg -y -i /data/temporary/localised_20201119-219-cniqnj/2minclock.m4v -vf 
select='isnan(prev_selected_t)+gte(t-prev_selected_t\,10)',fps=1/10 -s 283x159 
-pix_fmt yuvj420p -c:v mjpeg /data/temporary/transcode_20201119-2
19-kbzyx4/2minclocktest_%03d.jpeg


adding the fps filter after the select and setting it to the same value has so 
far given me the results I wanted.
Eg
Image 1 from very start
Image 2 from 10 second
Image 3 from 20 second
Etc.

Thanks very much for your help Moritz
Adam
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Re: [FFmpeg-user] Output a sequence of images with known timings

[adam smith via ffmpeg-user]

> On 19 Nov 2020, at 10:42, Moritz Barsnick  wrote:
> 
> Do take a look at the documentation of the select filter. It even has
> an example on how to extract certain frames, e.g. by number:
> 
> https://ffmpeg.org/ffmpeg-filters.html#select_002c-aselect 
> 
> 
>Select one frame every 100:
>select='not(mod(n\,100))'
> 
> Cheers,
> Moritz


Thanks Moritz, that’s really helpful I will take a look.

Much appreciated.

Adam
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Re: [FFmpeg-user] Output a sequence of images with known timings

[Moritz Barsnick]

On Wed, Nov 18, 2020 at 17:45:53 +, adam smith via ffmpeg-user wrote:

> My issue is that the first image time varies depending on the output fps.
> Eg fps=1/1 will output the first image from the 1st second of source; and so 
> on.
> Fps=1/5 will output the first image from the 3rd second of the source.
> Fps=1/11 will output the first image from the 6th second of the source.
> It keeps getting further away from the start while remaining approx halfway 
> to the point I expected.

That seems to be the expected behavior from the fps filter's averaging.

> Any ideas how I force the first image to either be the first frame of the 
> source, or the same value as the frequency?

Do take a look at the documentation of the select filter. It even has
an example on how to extract certain frames, e.g. by number:

https://ffmpeg.org/ffmpeg-filters.html#select_002c-aselect

Select one frame every 100:
select='not(mod(n\,100))'

Cheers,
Moritz
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[FFmpeg-user] Output a sequence of images with known timings

[adam smith via ffmpeg-user]

Hi,

I am trying to extract an image at set intervals from a video source. Later I 
will select one of images and will use the interval time and image number to 
determine the time in the video it came from.

If anybody has a better idea how to do this, feel free to stop me and push me 
in the right direction.

My issue is that the first image time varies depending on the output fps.
Eg fps=1/1 will output the first image from the 1st second of source; and so on.
Fps=1/5 will output the first image from the 3rd second of the source.
Fps=1/11 will output the first image from the 6th second of the source.
It keeps getting further away from the start while remaining approx halfway to 
the point I expected.

Any ideas how I force the first image to either be the first frame of the 
source, or the same value as the frequency?

Maybe I would be better off getting it to seek to each spot; but that would get 
pretty long pretty quick.

Full Command: ffmpeg -y -i 
/data/temporary/localised_20201118-961-d41yxx/2minclock.m4v  -filter_complex 
\"[0:0]fifo[vout];[vout]fps=fps=1/11[vout1]\" -map \"[vout1]\" -s 283x159 
-frames:v 60 -pix_fmt yuvj420p -c:v mjpeg  
/data/temporary/transcode_20201118-961-1qrmsyq/2minclocktest_%03d.jpeg"}

Console output:
/usr/src/app # ffmpeg -y -i 
/data/temporary/localised_20201118-961-d41yxx/2minclock.m4v  -filter_complex 
"[0:0]fifo[vout];[vout]fps=fps=1/11[vout1]" -map "[vout1]" -s 283x159 -frames:v 
60 -pix_fmt yuvj420p -c:v mjpeg /data/temporary/tra
nscode_20201118-961-1qrmsyq/2minclocktest_%03d.jpeg
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9.3.0 (Alpine 9.3.0)
  configuration: --disable-debug --disable-doc --disable-ffplay --enable-shared 
--enable-avresample --enable-libopencore-amrnb --enable-libopencore-amrwb 
--enable-gpl --enable-libass --enable-fontconfig --enable-libfreetype 
--enable-libvidstab --enable-libmp3lame --enable-libopus --enable-libtheora 
--enable-libvorbis --enable-libvpx --enable-libwebp --enable-libxcb 
--enable-libx265 --enable-libxvid --enable-libx264 --enable-nonfree 
--enable-openssl --enable-libfdk_aac --enable-postproc --enable-small 
--enable-version3 --enable-libbluray --enable-libzmq --extra-libs=-ldl 
--prefix=/opt/ffmpeg --enable-libopenjpeg --enable-libkvazaar --enable-libaom 
--extra-libs=-lpthread --enable-libsrt --extra-cflags=-I/opt/ffmpeg/include 
--extra-ldflags=-L/opt/ffmpeg/lib
  libavutil  56. 51.100 / 56. 51.100
  libavcodec 58. 91.100 / 58. 91.100
  libavformat58. 45.100 / 58. 45.100
  libavdevice58. 10.100 / 58. 10.100
  libavfilter 7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale  5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc55.  7.100 / 55.  7.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 
'/data/temporary/localised_20201118-961-d41yxx/2minclock.m4v':
  Metadata:
major_brand : M4V 
minor_version   : 1
compatible_brands: M4V M4A isommp42
creation_time   : 2020-11-18T12:36:47.00Z
encoder : Keynote 10.3.5 (7029.5.5)
  Duration: 00:02:01.20, start: 0.00, bitrate: 1420 kb/s
Stream #0:0(und): Video: h264 (avc1 / 0x31637661), yuv420p(tv, bt709), 
1920x1080 [SAR 1:1 DAR 16:9], 1415 kb/s, 50 fps, 50 tbr, 50 tbn, 100 tbc 
(default)
Metadata:
  creation_time   : 2020-11-18T12:36:47.00Z
  handler_name: Core Media Video
Stream mapping:
  Stream #0:0 (h264) -> fifo
  fps -> Stream #0:0 (mjpeg)
Press [q] to stop, [?] for help
[swscaler @ 0x55efa99b2d80] deprecated pixel format used, make sure you did set 
range correctly
Output #0, image2, to 
'/data/temporary/transcode_20201118-961-1qrmsyq/2minclocktest_%03d.jpeg':
  Metadata:
major_brand : M4V 
minor_version   : 1
compatible_brands: M4V M4A isommp42
encoder : Lavf58.45.100
Stream #0:0: Video: mjpeg, yuvj420p(pc), 283x159 [SAR 848:849 DAR 16:9], 
q=2-31, 200 kb/s, 0.09 fps, 0.09 tbn, 0.09 tbc (default)
Metadata:
  encoder : Lavc58.91.100 mjpeg
Side data:
  cpb: bitrate max/min/avg: 0/0/20 buffer size: 0 vbv_delay: N/A
frame=   11 fps=2.1 q=1.6 Lsize=N/A time=00:02:01.00 bitrate=N/A speed=22.9x
video:80kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing 
overhead: unknown

Thanks very much for any advice.
Adam
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