www.threekit.com/blog/gltf-everything-you-need-to-know comparision of several formats
With Telescopes however, it is possible. www.quora.com/Can-we-distinguish-individual-stars-in-other-galaxies-or-would-it-be-equivalent-to-say-we-know-there-are-other-forests-of-stars-galaxies-but-we-cant-tell-the-individual-trees-stars-What-is-the-farthest-individual/answer/Jerzy-Micha%C5%82-Pawlak contains an amazing answer that mentions two special cases of the furthest ones:
- gravitational lensing observation
- a star that is far but visible because its light is reflected by a nearby nebulae
But what we can definitely see are globular clusters of galaxies. E.g. the article en.wikipedia.org/wiki/Messier_87 basically gauges the size of galaxies by the number of globular clusters that they contain.
Sample usage by Andy Matuschak (possible coiner): notes.andymatuschak.org/About_these_notes
Previously on EdX: www.edx.org/learn/quantum-physics-mechanics/delft-university-of-technology-topology-in-condensed-matter-tying-quantum-knots "DelftX: Topology in Condensed Matter: Tying Quantum Knots".
But then they regained their sanity and put the source code on GitHub: github.com/topocm/topocm_content and is CC BY-SA.
Wiki without notability requirements by 
Ciro Santilli 35 Updated 2024-12-23 +Created 1970-01-01
Ciro Santilli 35 Updated 2024-12-23 +Created 1970-01-01Proponent of evergreen notes.
He's also curious about quantum computing: quantum.country/ like Ciro Santilli. Some crazy overlaps we get.
Filter graphs are a thing of great beauty. What an amazingly obscure domain-specific language, but which can produce striking results with very little!!!
A quick example from stackoverflow.com/questions/59551013/how-to-generate-stereo-sine-wave-using-ffmpeg-with-different-frequencies-for-eac/77730492#77730492 illustrates some of the fundamentals:
ffplay -autoexit -nodisp -f lavfi -i '
sine=frequency=500[a];
sine=frequency=1000[b];
[a][b]amerge, atrim=end=2
' +--------+
[sine=frequency=500]--->[a]-->| |
| amerge |-->[atrim]-->[output]
[sine=frequency=1000]-->[b]-->| |
+--------+So we see the following syntax patterns:
sine,amergeandatrimare filterssine=frequency=500: the first=says "araguments follow"frequency=500sets thefrequencyargument of thesinefilter- for multiple arguments the syntax is to separate arguments with colons e.g.
sine=frequency=500:duration=2
;: separates statements[a],[b]: sets the name of an edge,: creates unnamed edge between filters that have one input and one output
A list of all filters can be obtained ith:and parameters for a single filter can be obtained with:Related question: stackoverflow.com/questions/69251087/in-ffmpeg-command-line-how-to-show-all-filter-settings-and-their-parameters-bef
ffmpeg -filtersffmpeg --help filter=sineTODO dump graph to ASCII art? trac.ffmpeg.org/wiki/FilteringGuide#Visualizingfilters mentions a
-dumpgraph option, but haven't managed to use it yet.Bibliography:
- ffmpeg.org/ffmpeg-filters.html official documentation
- trac.ffmpeg.org/wiki/FilteringGuide some handy tips from the FFMpeg Wiki
Awesome tool to view quick stuff quickly without generating files. Unfortunately it doesn't support all options that the ffmpeg CLI supports, e.g. ffplay multiple input files. One day, one day.
Simple sines and variants:
- unix.stackexchange.com/questions/82112/stereo-tone-generator-for-linux/536860#536860
- stackoverflow.com/questions/5109038/linux-sine-wave-audio-generator/57610684#57610684
- superuser.com/questions/724391/how-to-generate-a-sine-wave-with-ffmpeg
- stackoverflow.com/questions/59551013/how-to-generate-stereo-sine-wave-using-ffmpeg-with-different-frequencies-for-eac/77730492#77730492
2 second 1000 Hz:
ffmpeg -f lavfi -i "sine=f=1000:d=2" out.wavVideo with a solid color:
- 2 second white video:Also add some audio:
ffplay -autoexit -f lavfi -i 'color=white:640x480:d=3,format=rgb24,trim=end=2'TODO how to ffplay the video + audio directly?ffmpeg -lavfi "color=white:640x480:d=3,format=rgb24,trim=end=2[v];sine=f=1000:d=2[a]" -map '[a]' -map '[v]' out.mkv-mapdoes not seem to work unfortunately. - 2 second white followed by 2 second black video:
ffplay -autoexit -f lavfi -i 'color=white:640x480:d=3,format=rgb24,trim=end=2[a];color=black:640x480:d=3,format=rgb24,trim=end=2[b];[a][b]concat=n=2:v=1:a=0' - bibliography:
Display count in seconds on the video:
- black text on white background. Start from 0 and count up to 2:
ffplay -autoexit -f lavfi -i " color=white:480x480:d=3, format=rgb24, drawtext= fontcolor=black: fontsize=600: text='%{eif\:t\:d}': x=(w-text_w)/2: y=(h-text_h)/2 " - bibliography:
Check which you you have:Tested on Ubuntu 23.10 I see:which means I have GNOME Display Manager.
systemctl status display-manager.service● gdm.service - GNOME Display Manager
Loaded: loaded (/lib/systemd/system/gdm.service; static)
Active: active (running) since Sun 2023-12-24 10:34:50 GMT; 23min ago
Process: 1827 ExecStartPre=/usr/share/gdm/generate-config (code=exited, status=0/SUCCESS)
Main PID: 1850 (gdm3)
Tasks: 4 (limit: 71817)
Memory: 6.8M
CPU: 119ms
CGroup: /system.slice/gdm.service
└─1850 /usr/sbin/gdm3 General-purpose computing on graphics processing units by Ciro Santilli 35 Updated 2024-12-23 +Created 1970-01-01
Ciro Santilli 35 Updated 2024-12-23 +Created 1970-01-01 Unlisted articles are being shown, click here to show only listed articles.