Question

I am trying to get a poster frame from a video file, using ffmpeg.

I have been following this tutorial and come up with the following code(which is taken/adapted from the link I gave):

public bool GetVideoThumbnail(string path, string saveThumbnailTo, int seconds)
        {
            string parameters = string.Format("-i {0} {1} -vcodec mjpeg -ss {2} -vframes 1 -an -f rawvideo", path, saveThumbnailTo, seconds);

            if (File.Exists(saveThumbnailTo))
            {
                return true;
            }
            else
            {
                using (Process process = Process.Start(pathToConvertor, parameters))
                {
                    process.WaitForExit();
                }
                return File.Exists(saveThumbnailTo);
            }
        }

At the moment this code is successfully creating a file in the correct destination (saveThumbnailTo) only the picture is completely black. I have tried changing the seconds value in the code to ensure that I am not just getting a blank picture from the start of the video. The path refers to where my video is stored, by the way.

I am currently calling the above code like so:

GetVideoThumbnail(videoPath, folderPath + "/poster.jpg", 100)

..and then passing it out to my view to display the picture. I just wonder whether “.jpg” is the extension I should be giving to this file as I am not entirely sure?

Edit: When I run the same command from the command line I get the following errors:

Incompatible pixel format ‘yuv420p’ for codec ‘mjpeg’, auto-selecting
format ‘yuvj420p’

which appears in yellow, and

[image2 @ 02S96AE0] Could not get frame filename number 2 from pattern
‘poster.jpg’ an_interleaved_write_frame(): Invalid argument

which appears in red.

Could anyone help me with getting this working properly as I am completely unfamiliar with the ffmpeg command line and not sure what I am doing wrong. I have tried removing the vcodec parameter and get the same error message.

Answer 1

Try this:

public bool GetVideoThumbnail(string path, string saveThumbnailTo, int seconds)
{
    string parameters = string.Format("-ss {0} -i {1} -f image2 -vframes 1 -y {2}", seconds, path, saveThumbnailTo);

    var processInfo = new ProcessStartInfo();
    processInfo.FileName = pathToConvertor;
    processInfo.Arguments = parameters;
    processInfo.CreateNoWindow = true;
    processInfo.UseShellExecute = false;

    File.Delete(saveThumbnailTo);

    using(var process = new Process())
    {
        process.StartInfo = processInfo;
        process.Start();
        process.WaitForExit();
    }

    return File.Exists(saveThumbnailTo);
}

Short explanation:

• f image2 : output is image
• vframes 1 : take one frame from the input
• y : overwrite output file
• “processInfo.CreateNoWindow = true” : do not show the ffmpeg window

Try several times with different values for the “seconds” parameter.
Also, make sure the “pathToConvertor” is correct.

This worked for me, with recent build of ffmpeg.exe on a Windows machine.

Let me know how it goes.