How to use a Pipe between two processes in Process.Start

Question

I have to run this command line using VB.NET:

"H:\videotest\test.vpy" - -y | "H:\Release\data\bin64\ffmpeg.exe" -hwaccel auto -y -i - -map 0:v:0 -c:v libx265 -crf 20.0 -preset 5 -x265-params level=0:profile=undefined:pmode:no-pme:pme:no-high-tier:ref=3:bframes=4:open-gop:keyint=250:min-keyint=25:b-adapt=2:bframe-bias=0:rc-lookahead=20:no-scenecut:b-pyramid:me=hex:subme=2:merange=57:temporal-mvp:weightp:no-weightb:max-merge=2:no-weightb:no-rect:no-amp:vbv-bufsize=0:vbv-maxrate=0:vbv-init=0.9:no-strict-cbr:qcomp=0.6:qstep=4:aq-mode=1:aq-strength=1.0:cutree:no-early-skip:min-cu-size=8:ctu=64:no-fast-cfb:ipratio=1.4:pbratio=1.3:cbqpoffs=0:crqpoffs=0:rd=3:psy-rd=0.3:psy-rdoq=1:no-b-intra:no-fast-intra:rdoq-level=1:no-tskip:no-tskip-fast:cu-lossless:tu-intra-depth=1:tu-inter-depth=1:strong-intra-smoothing:no-constrained-intra:nr-intra=0:nr-inter=0:qblur=0.5:cplxblur=20:signhide:sar=16 "H:\videotest\outputawdwd.mkv"

vspipe.exe runs the test.vpy script and applies filters to or resizes video input, then the output is piped to ffmpeg for the encoding.

If I use a normal Process declaration with vspipe it gives the following error:

Unknown argument: |

From the command line the script works well. I suspect that means that I have to manually pipe between vspipe and ffmpeg.

Is it possible to manually pipe output from one process to another? Must I do it manually?

Here is my function to start process:

executablepath = "H:\Project\VapourSynth\core64\vspipe.exe"

params = "H:\videotest\test.vpy" - -y | "H:\Release\data\bin64\ffmpeg.exe" -hwaccel auto -y -i - -map 0:v:0 -c:v libx265 -crf 20.0 -preset 5 -x265-params level=0:profile=undefined:pmode:no-pme:pme:no-high-tier:ref=3:bframes=4:open-gop:keyint=250:min-keyint=25:b-adapt=2:bframe-bias=0:rc-lookahead=20:no-scenecut:b-pyramid:me=hex:subme=2:merange=57:temporal-mvp:weightp:no-weightb:max-merge=2:no-weightb:no-rect:no-amp:vbv-bufsize=0:vbv-maxrate=0:vbv-init=0.9:no-strict-cbr:qcomp=0.6:qstep=4:aq-mode=1:aq-strength=1.0:cutree:no-early-skip:min-cu-size=8:ctu=64:no-fast-cfb:ipratio=1.4:pbratio=1.3:cbqpoffs=0:crqpoffs=0:rd=3:psy-rd=0.3:psy-rdoq=1:no-b-intra:no-fast-intra:rdoq-level=1:no-tskip:no-tskip-fast:cu-lossless:tu-intra-depth=1:tu-inter-depth=1:strong-intra-smoothing:no-constrained-intra:nr-intra=0:nr-inter=0:qblur=0.5:cplxblur=20:signhide:sar=16 "H:\videotest\outputawdwd.mkv"

Private Sub CreateJobProcess(ByVal Name, ByVal executablepath, ByVal params)

    Try

        If Not jobs_processes.ContainsKey(Name) Then

            Dim Proc As New Process

            Proc.StartInfo.UseShellExecute = False
            Proc.StartInfo.CreateNoWindow = True
            Proc.StartInfo.RedirectStandardError = True
            Proc.StartInfo.FileName = "" & executablepath & ""
            Proc.StartInfo.Arguments = params

            'start process
            Proc.Start()

            'add new process to dictionary
            jobs_processes.Add(Name, Proc)

            'TEMP
            My.Settings.giobbe -= 1

            'start background workers for statistics
            If Not ConversionStats.IsBusy Then
                ConversionStats.WorkerSupportsCancellation = True
                ConversionStats.RunWorkerAsync()
            End If

            If Not UpdateListJob.IsBusy Then
                UpdateListJob.WorkerSupportsCancellation = True
                UpdateListJob.RunWorkerAsync()
            End If

        End If

    Catch ex As Exception
        Me.Invoke(New MethodInvoker(Sub() Logbox.AppendText(Environment.NewLine & ">Program exception:" & Environment.NewLine & ex.Message & Environment.NewLine)))
        MsgBox(ex.Message)
    End Try
End Sub

Update:

This is the block I have changed, this function get job name and parameters for the job that needs to be created, then it saves the process in a dictionary.

              Dim Proc As New Process

                Proc.StartInfo.UseShellExecute = False
                Proc.StartInfo.CreateNoWindow = True
                Proc.StartInfo.RedirectStandardError = True
                Proc.StartInfo.FileName = "cmd"
                Proc.StartInfo.Arguments = params

                'start process
                Proc.Start()

                'add new process to dictionary
                jobs_processes.Add(Name, Proc)

                'TEMP
                My.Settings.giobbe -= 1

                'start background workers for statistics
                If Not ConversionStats.IsBusy Then
                    ConversionStats.WorkerSupportsCancellation = True
                    ConversionStats.RunWorkerAsync()
                End If

                If Not UpdateListJob.IsBusy Then
                    UpdateListJob.WorkerSupportsCancellation = True
                    UpdateListJob.RunWorkerAsync()
                End If

then i have a backgroundworker ( ConversionStats ) that get stderr from every process in the dictionary and print them into textboxes:

           'take current selected process and set streamreader
            Dim tmpproc As Process = jobs_processes(CurrentJob)
            Dim ffmpeg_stats As StreamReader
            Dim stdoutput As String = ""

            'something that verify if the job is started 

            If statejob = 1 Then    'if job is working

                'take stderr from ffmpeg
                ffmpeg_stats = tmpproc.StandardError
                stdoutput = ffmpeg_stats.ReadLine()

                If stdoutput IsNot Nothing Then 'if ffmpeg stderr is not nothing 

                    'IF FFMPEG IS RETURNING STATS
                    If stdoutput.Contains("frame=") Or stdoutput.Contains("size=") Then

so this is my code... but now with cmd getting standarderror with streamreader result in taking a string "Invalid Handle." this is an error from cmd stderr or there is a problem with the streamreader?

UPDATE 2

I have even tried to start a clean cmd process declaring only parameters but the result is just the console with main infos.

Microsoft Windows [Versione 6.3.9600] (c) 2013 Microsoft Corporation. Tutti i diritti riservati.

H:\Project\bin\Release>

this is the code to clarify:

                Dim Proc As New Process

                Proc.StartInfo.FileName = "cmd"
                Proc.StartInfo.Arguments = params

                'start process
                Proc.Start()

SO AGAIN THERE IS SOMEONE WHO CAN GUIDE ME HOW TO PIPE/REDIRECT STDOUTPUT FROM ONE PROCESS (vspipe.exe) TO THE STDIN OF ANOTHER PROCESS (ffmpeg.exe)?

Answer 1

Since you know your command string works on the command line, the easiest thing to do would be to let cmd.exe run the code for you. As Plutonix suggested in his comment, in this answer, Mark provides an example of how to do this in C# code.

Process test = new Process();
test.StartInfo.FileName = "cmd";
test.StartInfo.Arguments = @"/C ""echo testing | grep test""";
test.Start();

Adapting this to your purposes, and translating to VB.net might look something like this (using the same variables you declared in your code):

Dim Proc As New Process()
Proc.StartInfo.FileName = "cmd"
Proc.StartInfo.Arguments = "/C """ & executablepath & " " & params & """
Proc.Start()

How does this differ from what you were doing previously? You used Process.Start to run vspipe.exe, and then passed it your params. This new code above uses Process.Start to instead run cmd.exe, opening a command prompt window essentially, and inputting your complete command line string.

Receiving stdout and stderr requires two steps. First you have to set the 'redirect' properties for each to True, then after starting the process, manually retrieve the desired output.

Dim Proc As New Process()
Proc.StartInfo.FileName = "cmd"
Proc.StartInfo.Arguments = executablepath & " " & params

'Capture stdio & stderr:
Proc.StartInfo.RedirectStandardOutput = True
Proc.StartInfo.RedirectStandardError = True

Proc.Start()

'Read stdio & stderr:
Dim StdIO As String = Proc.StandardOutput.ReadToEnd()
Dim StdErr As String = Proc.StandardError.ReadToEnd()

• RedirectStandardOutput Property
• RedirectStandardError Property

RE: UPDATE 2:

The problem in this specific case is that the Arguments string is a mess of double quotes, which must be escaped. In vb.net this is done with double double-quotes (""), which can appear as "triple double-quotes" (""") if they are at the beginning or end of a string, or even longer multiples of double quotes if there are many that need to be escaped.

Although I do not have the specific software necessary on my system to test, the following should work:

Dim Proc As New Process
Proc.StartInfo.CreateNoWindow = True
Proc.StartInfo.UseShellExecute = False
Proc.StartInfo.FileName = "cmd"
Proc.StartInfo.Arguments = "/C ""H:\Project\VapourSynth\core64\vspipe.exe ""H:\videotest\test.vpy"" - -y | ""H:\Release\data\bin64\ffmpeg.exe"" -hwaccel auto -y -i - -map 0:v:0 -c:v libx265 -crf 20.0 -preset 5 -x265-params level=0:profile=undefined:pmode:no-pme:pme:no-high-tier:ref=3:bframes=4:open-gop:keyint=250:min-keyint=25:b-adapt=2:bframe-bias=0:rc-lookahead=20:no-scenecut:b-pyramid:me=hex:subme=2:merange=57:temporal-mvp:weightp:no-weightb:max-merge=2:no-weightb:no-rect:no-amp:vbv-bufsize=0:vbv-maxrate=0:vbv-init=0.9:no-strict-cbr:qcomp=0.6:qstep=4:aq-mode=1:aq-strength=1.0:cutree:no-early-skip:min-cu-size=8:ctu=64:no-fast-cfb:ipratio=1.4:pbratio=1.3:cbqpoffs=0:crqpoffs=0:rd=3:psy-rd=0.3:psy-rdoq=1:no-b-intra:no-fast-intra:rdoq-level=1:no-tskip:no-tskip-fast:cu-lossless:tu-intra-depth=1:tu-inter-depth=1:strong-intra-smoothing:no-constrained-intra:nr-intra=0:nr-inter=0:qblur=0.5:cplxblur=20:signhide:sar=16 ""H:\videotest\outputawdwd.mkv"""
Proc.StartInfo.RedirectStandardOutput = True
Proc.StartInfo.RedirectStandardError = True

Proc.Start()
Dim so As String = Proc.StandardOutput.ReadToEnd
Dim se As String = Proc.StandardError.ReadToEnd
Proc.WaitForExit()