从ffmpeg stdout管道的单个流中获取多个图像 [英] getting mulitple images from a single stream piped from ffmpeg stdout
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问题描述
我开始一个过程,用ffmpeg从视频文件中检索几帧,
I start a process to retrieve a few frames from a video file with ffmpeg,
ffmpeg -i "<videofile>.mp4" -frames:v 10 -f image2pipe pipe:1
并将图像管道到stdout -
and pipe the images to stdout -
var cmd = Process.Start(p);
var stream = cmd.StandardOutput.BaseStream;
var img = Image.FromStream(stream);
以这种方式获取第一张照片,但是如何获得所有图像?
Getting the first image this way works, but how do I get all of them?
推荐答案
OK这是gobspackingly容易,有点尴尬我在这里问。我会发布答案,以防其他人有所帮助。
OK this was gobspackingly easy, kind of embarrassed I asked here. I'll post the answer in case it will help anyone else.
每次有新图像时,流中的前几个字节将被重复。我猜想前8个会做,瞧瞧。
The first few bytes in the stream will be repeated every time there is a new image. I guessed the first 8 would do and voila.
static IEnumerable<Image> GetThumbnails(Stream stream)
{
byte[] allImages;
using (var ms = new MemoryStream())
{
stream.CopyTo(ms);
allImages = ms.ToArray();
}
var bof = allImages.Take(8).ToArray(); //??
var prevOffset = -1;
foreach (var offset in GetBytePatternPositions(allImages, bof))
{
if (prevOffset > -1)
yield return GetImageAt(allImages, prevOffset, offset);
prevOffset = offset;
}
if (prevOffset > -1)
yield return GetImageAt(allImages, prevOffset, allImages.Length);
}
static Image GetImageAt(byte[] data, int start, int end)
{
using (var ms = new MemoryStream(end - start))
{
ms.Write(data, start, end - start);
return Image.FromStream(ms);
}
}
static IEnumerable<int> GetBytePatternPositions(byte[] data, byte[] pattern)
{
var dataLen = data.Length;
var patternLen = pattern.Length - 1;
int scanData = 0;
int scanPattern = 0;
while (scanData < dataLen)
{
if (pattern[0] == data[scanData])
{
scanPattern = 1;
scanData++;
while (pattern[scanPattern] == data[scanData])
{
if (scanPattern == patternLen)
{
yield return scanData - patternLen;
break;
}
scanPattern++;
scanData++;
}
}
scanData++;
}
}
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