trim mp4 file in asp

Question

I need to write an ASP handler that will return a trimmed mp4 video file. I will specify filename, starting time and ending time.

Right now I only have handler that returns whole video file. The question is how to cut it in pieces.

public void ProcessRequest(HttpContext context)
{
    fileName = context.Request.QueryString["filename"];
    start = float.Parse(context.Request.QueryString["start"]);
    end = float.Parse(context.Request.QueryString["end"]);

    context.Response.ContentType = "video/mp4";
    context.Response.WriteFile("~/videofile.mp4");
}

I have read some topics on MP4 files, headers etc, but it's not that easy. If I found a way to calculate bytes for individual frames. But how to do it with variable bitrate?

Answer 1

If you can run a system command to run a command line utility like ffmpeg to cut the file for you. That is the simplest way.

 ffmpeg -i input-file -ss <start time> -t <duration>  -acodec copy -vcodec copy out.mp4 

It is otherwise too much trouble to trim the mp4 programatically. Let ffmpeg do it for you.

Answer 2

I managed to copy some part of the file using simple calculations based on metadata acquired with MediaInfo.

I copy whole header and then part of video and audio streams. But this only works if I start at the beginning of the video. When I want it to start after 2secs, the file is totally corrupted.

Also, header metadata says it's still original duration, even if it's only 4 secs.

Seeking is also quite inaccurate. Video is approx 10% longer that it should be.

Maybe there is some way to find seekpoints in stream?