get image from video stream in C#

Question

I am trying to get image from a stream (MemoryStream to be more precise). I can not find anything from Microsoft that can solve my problem. I am getting my streams from SQL so if there is some way to get an image from there, it will be OK. I have checked ffmpeg and the problem is that I need to save the video files. The files can reach up to 2GB and if there is a way not writing to the disk it will be helpful. If there is a way to read only the first 10MB or other limited size and read the image from it, that can also be a solution.

Answer 1

Video feed might be as simple as raw uncompressed video frames side by side to more complex multiplexed file format compatible chunk of data, eg .MP4 file. While the former case might be pretty simple, the latter requires you to demultiplex the file, seek within the stream, start decoding, possibly skip a few frames, then grab the frame of interest. The point is that it might be not as simple as it seems.

Video processing APIs in Windows are DirectShow, Media Foundation. With DirectShow it is possible to create a custom data source on top of SQL backed data stream and stream from there fetching DB data on demand, using API interfaces components (stock and third party) to do the rest of the task.

Answer 2

It is possible to capture frames with free VideoConverter for .NET that actually is a wrapper to FFMpeg tool. The idea is using live streaming capabilities (to C# Stream) of VideoConverter for special FFMpeg format "rawvideo" that actually is bitmap stream that can be processed by C# program, something like that:

var videoConv = new FFMpegConverter();
var ffMpegTask = videoConv.ConvertLiveMedia(
    "input.mp4",
    null, // autodetect live stream format
    rawBmpOutputStream,  // this is your special stream that will capture bitmaps
    "rawvideo",
    new ConvertSettings() {
        VideoFrameSize = "320x200",  // lets resize to exact frame size
        CustomOutputArgs = " -pix_fmt bgr24 ", // windows bitmap pixel format
        VideoFrameRate = 5, // lets consume 5 frames per second
        MaxDuration = 5 // lets consume live stream for first 5 seconds
    });

VideoConverter can read live streams from another .NET Stream (if input format can be used with live stream conversion).