【发布时间】：2017-01-22 23:51:21
【问题描述】：
我正在构建一个从视频中截取屏幕截图的程序。 它从视频中提取帧（使用 ffmpeg），然后将它们合并到一个文件中。
一切正常，除了有时我得到（几乎）黑色图像，主要是在视频的开头和结尾。
我能想到的一个可能的解决方案是检测提取的帧是否是暗的。如果天很黑，请从稍有不同的时间提取另一帧。
如何检测提取的帧是否为深色/黑色？还是有其他方法可以解决这个问题？
private void getScreenshots_Click(object sender, EventArgs e)
{
int index = 0;
foreach (string value in this.filesList.Items)
{
string file = selectedFiles[index] + "\\" + value;
// ------------------------------------------------
// MediaInfo
// ------------------------------------------------
// https://github.com/Nicholi/MediaInfoDotNet
//
// get file width, height, and frame count
//
// get aspect ratio of the video
// and calculate height of thumbnail
// using width and aspect ratio
//
MediaInfo MI = new MediaInfo();
MI.Open(file);
var width = MI.Get(StreamKind.Video, 0, "Width");
var height = MI.Get(StreamKind.Video, 0, "Height");
decimal d = Decimal.Parse(MI.Get(StreamKind.Video, 0, "Duration"));
decimal frameCount = Decimal.Parse(MI.Get(StreamKind.Video, 0, "FrameCount"));
MI.Close();
decimal ratio = Decimal.Divide(Decimal.Parse(width), Decimal.Parse(height));
int newHeight = Decimal.ToInt32(Decimal.Divide(newWidth, ratio));
decimal startTime = Decimal.Divide(d, totalImages);
//totalImages - number of thumbnails the final image will have
for (int x = 0; x < totalImages; x++)
{
// increase the time where the thumbnail is taken on each iteration
decimal newTime = Decimal.Multiply(startTime, x);
string time = TimeSpan.FromMilliseconds(double.Parse(newTime.ToString())).ToString(@"hh\:mm\:ss");
string outputFile = this.tmpPath + "img-" + index + x + ".jpg";
// create individual thumbnails with ffmpeg
proc = new Process();
proc.StartInfo.FileName = "ffmpeg.exe";
proc.StartInfo.Arguments = "-y -seek_timestamp 1 -ss " + time + " -i \"" + file + "\" -frames:v 1 -qscale:v 3 \"" + outputFile + "\"";
proc.Start();
proc.WaitForExit();
}
// set width and height of final image
int w = (this.cols * newWidth) + (this.spacing * this.cols + this.spacing);
int h = (this.rows * newHeight) + (this.spacing * this.rows + this.spacing);
int left, top, i = 0;
// combine individual thumbnails into one image
using (Bitmap bmp = new Bitmap(w, h))
{
using (Graphics g = Graphics.FromImage(bmp))
{
g.Clear(this.backgroundColor);
// this.rows - number of rows
for (int y = 0; y < this.rows; y++)
{
// put images on a column
// this.cols - number of columns
// when x = number of columns go to next row
for (int x = 0; x < this.cols; x++)
{
Image imgFromFile = Image.FromFile(this.tmpPath + "img-" + index + i + ".jpg");
MemoryStream imgFromStream = new MemoryStream();
imgFromFile.Save(imgFromStream, imgFromFile.RawFormat);
imgFromFile.Dispose();
left = (x * newWidth) + ((x + 1) * this.spacing);
top = (this.spacing * (y + 1)) + (newHeight * y);
g.DrawImage(Image.FromStream(imgFromStream), left, top, newWidth, newHeight);
i++;
}
}
}
// save the final image
bmp.Save(selectedFiles[index] + "\\" + value + ".jpg");
}
index++;
}
}
【问题讨论】：
标签： c# image-processing ffmpeg