DEV Community: ૮༼⚆︿⚆༽つ

List of helpful FFMPEG command for checking capabilities

૮༼⚆︿⚆༽つ — Thu, 11 Mar 2021 08:07:11 +0000

A lot of FFMPEG options are not in the documentations and only available to the specific build, hardware acceleration, or codecs. So I need a list of commands on how to show and search all available settings and options.

1. List all possible options of `-filter_complex` and `-vf` filter graph

ffmpeg -hide_banner -filters

Filters:
 A = Audio input/output
 V = Video input/output
 N = Dynamic number and/or type of input/output
 | = Source or sink filter

 T.. = Timeline support
 .S. = Slice threading
 ..C = Command support
 ---
 ... filter_name            N->N       Description.

1.2 Check filter details

ffmpeg -hide_banner -h filter=$fname

Filter lowpass
  Description.
    Inputs:
       … (…)
    Outputs:
       … (…)
lowpass AVOptions:
  options         <type>     ..F....... Description (default or range value)

2. List all hardware acceleration

ffmpeg -hide_banner -hwaccels

Hardware acceleration methods:
vdpau
cuda
vaapi
qsv
drm

3. List all encoders and/or decoders

ffmpeg -hide_banner -encoders
ffmpeg -hide_banner -decoders

Encoders/Decoders:
 V..... = Video
 A..... = Audio
 S..... = Subtitle
 .F.... = Frame-level multithreading
 ..S... = Slice-level multithreading
 ...X.. = Codec is experimental
 ....B. = Supports draw_horiz_band
 .....D = Supports direct rendering method 1
 ------
 ...... cname_hwaccel                 Description

3.0 List all codecs

ffmpeg -hide_banner -codecs

Codecs:
 D..... = Decoding supported
 .E.... = Encoding supported
 ..V... = Video codec
 ..A... = Audio codec
 ..S... = Subtitle codec
 ...I.. = Intra frame-only codec
 ....L. = Lossy compression
 .....S = Lossless compression
 ------
 ...... cname_hwaccel                 Description

3.1 Check encoders details

(can list multiple encoders depend on hardware acceleration you have)

ffmpeg -hide_banner -h encoder=$cname_hwaccel

Encoder libname [Description]:
    General capabilities: delay threads 
    Threading capabilities: auto
    Supported pixel formats: … … …
libname AVOptions:
  -option            <type>     .......... Description (default or range value)

 codec_name configuration using a :-separated list of key=value parameters


Encoder cname_hwaccel [Description]:
    General capabilities: delay hardware 
    Threading capabilities: none
    Supported hardware devices: …
    Supported pixel formats: … …
cname_hwaccel AVOptions:
  -option             <type>        E......... Description (default or range value)

3.2 Check decoder details

ffmpeg -hide_banner -h decoder=$cname

Decoder cname [Description]:
    General capabilities: dr1 delay threads 
    Threading capabilities: frame and slice
    Supported hardware devices: … … … 
cname Decoder AVOptions:
  -option         <type>    .D........ Description (default or range value)

Rust is not panacea

૮༼⚆︿⚆༽つ — Wed, 24 Feb 2021 09:25:38 +0000

Just my personal list on when writing software in Rust become a problem.

Rust grievances
https://gist.github.com/brendanzab/d41c3ae485d66c07178749eaeeb9e5f7
why esbuild written in Go
https://news.ycombinator.com/item?id=22336284
problem writing wayland compositor in Rust
http://way-cooler.org/blog/2020/01/09/way-cooler-post-mortem.html
switching to Rust can breaks things
https://drewdevault.com/2021/02/09/Rust-move-fast-and-break-things.html
Zig vs Rust
https://scattered-thoughts.net/writing/assorted-thoughts-on-zig-and-rust/
unnecessary syscalls produced by Rust compiler
https://drewdevault.com/2020/01/08/Re-Slow.html
Rust is faster than Javascript but mostly untrue when targeting web browser
https://zaplib.com/docs/blog_post_mortem.html
// Detect dark theme var iframe = document.getElementById('tweet-1520809822530142208-862'); if (document.body.className.includes('dark-theme')) { iframe.src = "https://platform.twitter.com/embed/Tweet.html?id=1520809822530142208&theme=dark" }
When Zig is safer and faster than Rust
https://zackoverflow.dev/writing/unsafe-rust-vs-zig/

Nix Multi-User Installation Without Default Channel

૮༼⚆︿⚆༽つ — Wed, 03 Feb 2021 14:53:10 +0000

Why do this?

Let's just say I want to restrict all users from polluting /nix/store but still allow them to use Nix toolchains.

Installation

fish

sh (curl -L https://nixos.org/nix/install | psub) --daemon

zsh

sh =(curl -L https://nixos.org/nix/install) --daemon

bash

sh <(curl -L https://nixos.org/nix/install) --daemon

Replace channel

When you list the channel in a normal way you will get an empty list.

nix-channel --list

However, when you run it as a superuser then you will see nixpkgs channel.

This channel is available to all users. Let's make this channel only accessible to you!

1. Remove default channel

sudo nix-channel --remove nixpkgs

2. Re-add channel

nix-channel --add https://nixos.org/channels/nixpkgs-unstable

3. Add yourself to the group

sudo groupadd -r nixbld
sudo useradd -c "Nix build user $USER" \
  -d /var/empty -g nixbld -G nixbld \
  -M -N -r -s "$(which nologin)" \
  nixbld_$USER

For fish user: remove " and $ so that it would be (which nologin)

4. Update nix channel and toolchains

To update channel

nix-channel --update

if you get a permission error and sysemctl status nix-daemon has FAIL messages, try rebooting your system

Optionally, upgrade all Nix toolchains

nix-env -iA nixpkgs.nix nixpkgs.cacert
systemctl daemon-reload
systemctl restart nix-daemon

5. Fixing NIX_PATH

Comment for #2033

nathanshelly commented on Dec 13, 2020

If I understand things correctly I believe your issues could be solved by adding the following line (which this issue is proposing should be included by default) to your $HOME/.zshrc (or other startup file depending on your preferences):

export NIX_PATH=$NIX_PATH:$HOME/.nix-defexpr/channels

I'm still learning Nix myself so I don't have context on why that is not the default already. Let me know if that doesn't work and we can try to keep debugging things 😄

View on GitHub

echo "export NIX_PATH=$NIX_PATH:$HOME/.nix-defexpr/channels" >> ~/.profile

(in my case, I add it to my .xprofile)

if you don't do this, nix-shell will complain:

Default Nix installations don't include user channels in NIX_PATH, causing inconsistent tool behavior #2033

grahamc posted on Apr 01, 2018

Should Nix installations include $HOME/.nix-defexpr/channels in the NIX_PATH? Should it appear before or after root channels?

nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs:nixos-config=/etc/nixos/configuration.nix:/nix/var/nix/profiles/per-user/root/channels

$ nix-channel --list             
nixpkgsunstable https://nixos.org/channels/nixpkgs-unstable

$ nix-env -iA nixpkgsunstable.git
installing 'git-minimal-2.16.2'

$ nix-shell -p nixpkgsunstable.git
error: undefined variable 'nixpkgsunstable' at (string):1:94
(use '--show-trace' to show detailed location information)

$ nix-shell '<nixpkgsunstable>' -p git
error: file 'nixpkgsunstable' was not found in the Nix search path (add it using $NIX_PATH or -I), at (string):1:94
(use '--show-trace' to show detailed location information)

$ nix-build '<nixpkgsunstable>' -A git
error: file 'nixpkgsunstable' was not found in the Nix search path (add it using $NIX_PATH or -I)

vs:

$ export NIX_PATH=$NIX_PATH:$HOME/.nix-defexpr/channels

$ nix-env -iA nixpkgsunstable.git    
replacing old 'git-minimal-2.16.2'
installing 'git-minimal-2.16.2'

$ nix-shell -p nixpkgsunstable.git    
error: undefined variable 'nixpkgsunstable' at (string):1:94
(use '--show-trace' to show detailed location information)

$ nix-shell '<nixpkgsunstable>' -p git

[nix-shell:~]$ exit

$ nix-build '<nixpkgsunstable>' -A git
/nix/store/jaani1kx4a4kvz11d0myfkjjiiklfl7w-git-2.16.2

With this configuration, and the explicitly specified nixpkgs, is it possible for users to override nixpkgs without redefining the NIX_PATH? Does it matter?

View on GitHub

TIPS: use nix-direnv for this

References

Current states of IoT development

૮༼⚆︿⚆༽つ — Tue, 15 Sep 2020 12:59:21 +0000

In the current state, you can build Web Apps in 5 days alone but you can't build a simple IoT solution in 1 week.

The current state doing web development is easy not only because there is many content/tutorial for that but also many great tooling that exists in the ecosystem (thanks to many Open Source project). Let's list what we have now in the Web Dev ecosystem.

Now in Front-End or Mobile development we have:

some framework that decent and have mature enough based on Component Design Pattern
hot module/reload. Change a small portion of code and the result will be shown in less than seconds regardless of how big/complex your codebase.
Static, dynamic, or duck typing language. Choose what suits you well
development can be framework and language agnostic thanks to WebComponent & WebAssembly
thousand library and hundred UI Components ready to use in many frameworks
rich debugging tools, you can even do time travel debugging, event there is built in the debugger in any popular browser now
rise of micro front-end architecture

and Back End development we have:

some backend framework has hot reload alike. (it's called Hot Code Swap)
many backend frameworks/libs became database agnostic
thanks to microservice pattern and docker, backend code can be written in any language
many tools for documenting, building, and inspecting API and data. (Swagger, GraphiQL, etc)
Design Pattern agnostic. (some depends on the language that you use)
advanced logging system

while in Embedded development (especially µC) we have:

language agnostic but depend on specific devices. (microphyton, nodejs johnyfive, STM32F4DISC, etc)
device agnostic but depend on language and abstraction layer. (EC++, Arduino)
nearly write once run anywhere can only be achieved using Arduino
low productivity because no live/hot reload thing. (exception if using Zephyr OS)
mostly concurrent programming can only be achieved if using RTOS by sacrificing significant memory

However, IoT development is not only about hardware. It's a combination of those three that makes IoT solution valuable. So, how to glue them together and avoid silos mistake?