Running External Programs in windows

New to Julia
1

hello,
I’m trying to capture an image from a webcam using Windows 10.
I have FFmpeg install and I can capture an image using the cmd command:
ffmpeg -f dshow -video_size 1920x1080 -i "video=HD Pro Webcam C920" -frames:v 1 org_img.jpg.
What I fail doing is running this command using the run command in julia script.
I tried calling it as follow:

        mycmd = @cmd """ffmpeg -f dshow -video_size 1920x1080 -i "video=HD Pro Webcam C920" -frames:v 1 org_img.jpg"""
        run(`cmd /c $mycmd`)

but I get the following error

'ffmpeg' is not recognized as an internal or external command,
operable program or batch file.
ERROR: failed process: Process(`cmd /c ffmpeg -f dshow -video_size 1920x1080 -i 'video=HD Pro Webcam C920' -frames:v 1 org_img.jpg`, ProcessExited(1)) [1]

Stacktrace:
 [1] pipeline_error
   @ .\process.jl:525 [inlined]
 [2] run(::Cmd; wait::Bool)
   @ Base .\process.jl:440
 [3] run(::Cmd)
   @ Base .\process.jl:438
 [4] top-level scope
   @ REPL[13]:1

so I tried:

        run(mycmd)

and got the following error

ERROR: IOError: could not spawn `ffmpeg -f dshow -video_size 1920x1080 -i 'video=HD Pro Webcam C920' -frames:v 1 org_img.jpg`: no such file or directory (ENOENT)
Stacktrace:
 [1] _spawn_primitive(file::String, cmd::Cmd, stdio::Vector{Any})
   @ Base .\process.jl:99
 [2] #637
   @ .\process.jl:112 [inlined]
 [3] setup_stdios(f::Base.var"#637#638"{Cmd}, stdios::Vector{Any})
   @ Base .\process.jl:196
 [4] _spawn
   @ .\process.jl:111 [inlined]
 [5] run(::Cmd; wait::Bool)
   @ Base .\process.jl:439
 [6] run(::Cmd)
   @ Base .\process.jl:438
 [7] top-level scope
   @ REPL[17]:1

I found that VideoIO.jl can capture images from a Webcam, so I tried that to, and faild :frowning:

import VideoIO
cam = VideoIO.opencamera()

and got the following error

ERROR: MethodError: no method matching unsafe_convert(::Type{Ptr{Ptr{VideoIO.libffmpeg.AVDictionary}}}, ::VideoIO.AVDict)
Closest candidates are:
  unsafe_convert(::Type{Ptr{T}}, ::Base.ReshapedArray{T, N, P, MI} where {N, P<:AbstractArray, MI<:Tuple{Vararg{Base.MultiplicativeInverses.SignedMultiplicativeInverse{Int64}, N} where N}}) where T at reshapedarray.jl:281
  unsafe_convert(::Type{Ptr{T}}, ::LinearAlgebra.Transpose{var"#s832", var"#s831"} where {var"#s832", var"#s831"<:(AbstractVecOrMat{T} where T)}) where T at C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\LinearAlgebra\src\adjtrans.jl:222
  unsafe_convert(::Type{Ptr{T}}, ::OffsetArrays.OffsetArray{T, N, AA} where {N, AA<:AbstractArray{T, N}}) where T at C:\Users\KOBIED\.julia\packages\OffsetArrays\I5Pfg\src\OffsetArrays.jl:454
  ...
Stacktrace:
 [1] avformat_open_input(ps::VideoIO.NestedCStruct{VideoIO.libffmpeg.AVFormatContext}, url::String, fmt::Ptr{VideoIO.libffmpeg.AVInputFormat}, options::VideoIO.AVDict)
   @ VideoIO.libffmpeg C:\Users\KOBIED\.julia\packages\VideoIO\EsW3Z\lib\libffmpeg.jl:8571
 [2] open_avinput(avin::VideoIO.AVInput{String}, source::String, input_format::Ptr{VideoIO.libffmpeg.AVInputFormat}, options::VideoIO.AVDict)
   @ VideoIO C:\Users\KOBIED\.julia\packages\VideoIO\EsW3Z\src\avio.jl:195
 [3] VideoIO.AVInput(source::String, input_format::Ptr{VideoIO.libffmpeg.AVInputFormat}, options::VideoIO.AVDict; avio_ctx_buffer_size::Int64)
   @ VideoIO C:\Users\KOBIED\.julia\packages\VideoIO\EsW3Z\src\avio.jl:218
 [4] VideoIO.AVInput(source::String, input_format::Ptr{VideoIO.libffmpeg.AVInputFormat}, options::VideoIO.AVDict)
   @ VideoIO C:\Users\KOBIED\.julia\packages\VideoIO\EsW3Z\src\avio.jl:207
 [5] opencamera(::String, ::Ptr{VideoIO.libffmpeg.AVInputFormat}, ::VideoIO.AVDict; kwargs::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ VideoIO C:\Users\KOBIED\.julia\packages\VideoIO\EsW3Z\src\avio.jl:1016
 [6] opencamera(::String, ::Ptr{VideoIO.libffmpeg.AVInputFormat}, ::VideoIO.AVDict) (repeats 2 times)
   @ VideoIO C:\Users\KOBIED\.julia\packages\VideoIO\EsW3Z\src\avio.jl:1016
 [7] top-level scope
   @ REPL[20]:1

The VideoIO.jl documentation and examples are quite poor so I have no idea how to continue.
Please Help !!!

2

It’s probably missing the path to the ffmpeg executable. Try to provide the complete path to ffmpeg, e.g. in my case this works except that it doesn’t find the webcam :wink: :

julia> mycmd = @cmd """D:/Data/Downloads/ffmpeg-4.2.1-win64-static/bin/ffmpeg -f dshow -video_size 1920x1080 -i "video=HD Pro Webcam C920" -frames:v 1 org_img.jpg"""
`D:/Data/Downloads/ffmpeg-4.2.1-win64-static/bin/ffmpeg -f dshow -video_size 1920x1080 -i 'video=HD Pro Webcam C920'
 -frames:v 1 org_img.jpg`

julia> run(`cmd /c $mycmd`)
ffmpeg version 4.2.1 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 9.1.1 (GCC) 20190807
...
3

thanks for the quick reply, that worked :tada: :tada:
I also found the FFMPEG.jl package, which did exactly as you suggested.

using MMFPEG
mycmd = @cmd """-f dshow -video_size 1920x1080 -i "video=HD Pro Webcam C920" -frames:v 1 org_img.jpeg"""
ffmpeg_exe(mycmd)

thanks again :slight_smile:

1 Like
4

Daniel, please do not be so quick to give up on VideoIO
In the early days VideoIO was a bear to use, I have done a lot of testing with it on Windows and found that it ‘just works’ now. Being honest I have not tried it for several months though , and not in 1.7

5

Johnh hello, on the contrary, I would be more then happy to be able to use the VidioIO.jl package.
Unfortunately I don’t understand way it’s not working. Using the run() command directly is a poor solution but it work for me.
If someone can help me with the VideoIO.jl package I’ll be more then happy to use it.
p.s. I’m working with julia v1.6

6

Update
Base.convert(::Type{Ref{Ptr{AVDictionary}}}, d::AVDict) = d.ref_ptr_dict
to
Base.cconvert(::Type{Ptr{Ptr{AVDictionary}}}, d::AVDict) = d.ref_ptr_dict

in avdictionary.jl which can be found at .julia/packages/videoio/somethingrandom/ src/avddictionary.jl , should start working hopefully