CreateProcess fails when dshow is used in commandline

user_6950434 0
Viewed 280

Trying to launch ffmpeg using CreateProcess.

Issues:

1) Can't use dshow in the commandline.

2) RTMP streaming with the STDIN piped don't show the stream.

Questions:

1) What are the ceveats in the commandline pertaining to CreateProcess api?

2) What's is the way round ? How can the issue be fixed?

This code works:

BOOL bSuccess = CreateProcess(NULL,
    L"ffmpeg.exe -y -loop 1 -i kites.jpg  out.mp4",         
    NULL,   
    NULL,
    TRUE, 
    CREATE_NEW_CONSOLE, 
    NULL, 
    NULL,
    &siStartInfo,
    &piProcInfo);

CreateProcess fails when dshow is used. However it works as command line in console.

BOOL bSuccess = CreateProcess(NULL,
    L"ffmpeg.exe -y -loop 1 -i kites.jpg  -f dshow  -i audio=\"Stereo Mix(Realtek High Definition Audio)\"  out.mp4",
    NULL,
    NULL,
    TRUE,
    CREATE_NEW_CONSOLE,
    NULL,
    NULL,
    &siStartInfo,
    &piProcInfo);

Edited: ( with absolute path, still no luck)

std::wstring cmdArgslistSetChannel = L"ffmpeg.exe -y -loop 1 -i c:\test\kites.jpg  -f dshow  -i audio=\"Stereo Mix(Realtek High Definition Audio)\"  out.mp4";
bSuccess = CreateProcess(NULL, 
        &cmdArgslistSetChannel[0],
        NULL,          
        NULL,          
        TRUE,          
        CREATE_NEW_CONSOLE,            
        NULL,          
        NULL,          
        &siStartInfo, 
        &piProcInfo);
ffmpeg winapi c++
2 Answers

You are almost there. You can specify the absolute path like so. Make sure the no whitespaces are present in the folder name, else ffmpeg command may fail again. If the ffmpeg is situated in another folder, you should specify the path too.

std::wstring cmdArgslistSetChannel = L"c:\test\ffmpeg.exe -y -loop 1 -i \"c:\\test\\kites.jpg\"  -f dshow  -i audio=\"Stereo Mix(Realtek High Definition Audio)\"  out.mp4";
user_67550830

First,

The immediate issue is simply that you need to escape backslashes.

Change:

c:\test\kites.jpg

To

c:\\test\\kites.jpg

'\t' is a tab and '\' is a backslash

Second,

from Comment:

From CreateProcessW: "The Unicode version of this function, CreateProcessW, can modify the contents of [the lpCommandLine] string. Therefore, this parameter cannot be a pointer to read-only memory (such as a const variable or a literal string). If this parameter is a constant string, the function may cause an access violation."

Therefore you need to hold the contents in a buffer like this:

std::wstring args{L"c:\test\ffmpeg.exe -y -loop 1 -i \"c:\\test\\kites.jpg\"  -f dshow  -i audio=\"Stereo Mix(Realtek High Definition Audio)\"  out.mp4"};

Third,

if you know full path to the executable (which it seems), you can benefit from putting that into the first parameter of CreateProcess instead. This will give you a little more control and diagnostics (in the future as well) as it is a more direct way of creating the process.

user_22615380
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