Only first frame is exported

[tigrouind]

Code to reproduce the issue

if (FFmpegLoader.Load(@"ffmpeg"))
{
    using (var writer = new VideoWriter(@"somefile.mp4"))
    using (var bitmap = new Bitmap(1920, 1080))
    using (var graphics = Graphics.FromImage(bitmap))
    {
        writer.Open();
        var audio = new float[writer.AudioSamplesPerFrame];

        Random rand = new Random();
        for (int i = 0; i < 1000; i++)
        {
            if (writer.WriteVideo)
            {
                var color = rand.Next(2) == 0 ? Brushes.Yellow : Brushes.Red;
                graphics.FillRectangle(color, 0, 0, 1920, 1080);
                writer.WriteVideoFrame(bitmap);
            }
            else
            {
                writer.WriteAudioFrame(audio);
            }
        }
    }
}

Expected result

The movie alternate between yellow and red frames.

Actual result

Only first frame is shown. Time length of movie seems correct (there is as many frames as expected).

Additionally

Here is a list of things that are not obvious and took me lot of time to figure out :

• it only works in 64-bit mode.
• the README contains a link to FFmpeg.AutoGen dlls which are newer than this project. Here is a link to same version as the one used by the library.
• excepted resolution is 1920 x 1080. If resolution of bitmap is not same as writer, it crashes by throwing an AccessViolationException. Instead, writer should throw a custom exception with an explicit message. It's possible to use a custom resolution by setting writer.Width and writer.Height before calling writer.Open().
• writer except you to call WriteVideoFrame() / WriteAudioFrame() alternatively. You are not supposed to call WriteVideoFrame() consecutively (even if video does not contains audio). Library should detect that and throw an exception (unless it is supported).

[Twometer]

Thanks for the report, can you try

1. using i % 2 == 0 instead of rand.Next() for the alternating images?
2. creating a new Bitmap for each frame instead of reusing it?

That'll help narrow it down, but I'll look into the other issues as well.

[tigrouind]

@Twometer :

1. Fun fact is my initial code example was using i % 2 == 0 but I edited it, fearing that WriteVideoFrame() would always end up on a odd or even value (thus using same color) because calls are interleaved with WriteAudioFrame().
2. I also tried that before but that does not help as well.