MathewSachin/Captura · error · Exception

Cannot connect Video pipe to FFmpeg

Error message

Cannot connect Video pipe to FFmpeg

What it means

Thrown by FFmpegWriter.WriteFrame (src/Captura.FFmpeg/Video/FFmpegVideoWriter.cs:216) when _ffmpegIn.WaitForConnection(5000) returns false on the first frame. FFmpeg must open the `captura-<guid>` video pipe within 5s; if it never does, the timeout fires. This is the first interaction with ffmpeg after StartFFmpeg, so a failure here usually means ffmpeg failed to start or rejected its arguments.

Source

Thrown at src/Captura.FFmpeg/Video/FFmpegVideoWriter.cs:216

        Task _lastFrameTask;

        /// <summary>
        /// Writes an Image frame.
        /// </summary>
        public void WriteFrame(IBitmapFrame Frame)
        {
            if (_ffmpegProcess.HasExited)
            {
                Frame.Dispose();
                throw new FFmpegException(_ffmpegProcess.ExitCode);
            }
            
            if (_firstFrame)
            {
                if (!_ffmpegIn.WaitForConnection(5000))
                {
                    throw new Exception("Cannot connect Video pipe to FFmpeg");
                }

                _firstFrame = false;
            }

            if (_lastFrameTask == null)
            {
                _lastFrameTask = Task.CompletedTask;
            }

            if (!(Frame is RepeatFrame))
            {
                using (Frame)
                {
                    if (Frame.Unwrap() is INV12Frame nv12Frame)
                    {
                        nv12Frame.CopyNV12To(_videoBuffer);
                    }

View on GitHub (pinned to 3fdf41529b)

Solutions

1. Check _ffmpegProcess.HasExited right after StartFFmpeg in the constructor; if dead, read the log immediately.
2. Confirm FFmpegExePath resolves to a real executable (not the fallback bare name).
3. Log argsBuilder.GetArgs() and reproduce the command manually.
4. Raise the 5000 ms connect timeout on slow machines.

Example fix

// before
if (!_ffmpegIn.WaitForConnection(5000))
    throw new Exception("Cannot connect Video pipe to FFmpeg");
// after
if (!_ffmpegIn.WaitForConnection(5000))
    throw new Exception(_ffmpegProcess.HasExited
        ? $"FFmpeg exited (code {_ffmpegProcess.ExitCode}) before opening the video pipe; args: {args}"
        : "Video pipe connect timed out after 5s");

// right after StartFFmpeg in the ctor, fail fast with the real reason
_ffmpegProcess = FFmpegService.StartFFmpeg(argsBuilder.GetArgs(), Args.FileName, out _);
if (_ffmpegProcess.HasExited) // ffmpeg rejected args and died immediately
    throw new FFmpegException(_ffmpegProcess.ExitCode);

try { /* first WriteFrame */ }
catch (Exception e) when (e.Message.Contains("Video pipe")) { var reason = _ffmpegProcess.HasExited ? $"exit {_ffmpegProcess.ExitCode}" : "timeout"; /* report reason */ }

When it happens

Trigger: The first WriteFrame call when ffmpeg did not connect to the video named pipe within 5000 ms. Typically ffmpeg exited immediately after start (bad args, missing binary resolution via FFmpegExePath) or is still alive but stalled.

Common situations: FFmpegExePath resolved to a bare `ffmpeg.exe` name that isn't on PATH; the rawvideo/nv12 args are malformed; ffmpeg process started but the named-pipe path format is wrong for this OS; system too loaded to start ffmpeg in 5s.

Related errors

• Cannot connect Audio pipe to FFmpeg
• FFmpeg could not be found. Please download using the in-buil
• An Error Occurred with FFmpeg, Exit Code: {ExitCode}.\nSee F
• FFmpeg could not be found. Please download using the in-buil
• An Error Occurred with FFmpeg, Exit Code: {ExitCode}.\nSee F

AI-assisted analysis of MathewSachin/Captura@3fdf41529b (2026-08-13). Data as JSON: /api/errors/5c06f26444e9e730. Report an issue: GitHub.