CODEWITHSUNDEEP
videoffmpeg
Will Ashworth
Will Ashworth

Reputation: 1088

Detect if "faststart" has been applied to video

When running "qt-faststart" on an MP4, you're essentially taking the meta data from the back and placing it at the front of the file. In my case, so Flash can properly start playing the video before it's fully done loading.

I have a large number of videos that I'm running through a shell script to encode overnight. When I upload, however, I won't necessarily know in my final folder of videos (on the server) have "qt-faststart" run on it.

My goal is to find the straggler videos and run qt-faststart on them manually, but I'll need a way to compile a list. Is there any way to check for this meta data information with PHP or something? Wondering how I can tell if a video has already had qt-faststart run on it or not.

Upvotes: 13

Views: 12640

Answers (3)

Nathan Smith
Nathan Smith

Reputation: 1813

Here is a small c# helper function.

This is a very basic solution and may not work with all video files but does work for my simple case where videos were encoded with a recent version of ffmpeg.

private bool IsVideoFastStartEnabled(string fullFilePath)
{
    /////////////////////////////////////////////////////////////////////////////////
    // Fast start is enabled if "moov" is before "mdat" in first 4096 bytes fo file
    // https://trac.ffmpeg.org/wiki/HowToCheckIfFaststartIsEnabledForPlayback
    /////////////////////////////////////////////////////////////////////////////////
            
    byte[] buffer = new byte[4096];
    using (FileStream fs = new FileStream(fullFilePath, FileMode.Open, FileAccess.Read))
    {
        fs.Read(buffer, 0, buffer.Length);
        fs.Close();
    }
    var byteSpan = buffer.AsSpan();
            
    var moovPattern = new byte[] { 0x6d, 0x6f, 0x6f, 0x76, 0x00 }.AsSpan();
    var moovIndex = byteSpan.IndexOf(moovPattern);

    var mdatPattern = new byte[] { 0x6d, 0x64, 0x61, 0x74, 0x00 }.AsSpan();
    var mdatIndex = byteSpan.IndexOf(mdatPattern);

    if (moovIndex > 0 && (mdatIndex == -1 || moovIndex < mdatIndex))
    {
        // Fast start is enabled
        return true;
    }
    return false;
}

Upvotes: 0

user1133275
user1133275

Reputation: 2735

mediainfo -f file.mp4 | grep IsStreamable

or

ffprobe  -v debug file.mp4  2>&1 | grep seeks

and

0 seeks

means "faststart" has been applied.

Upvotes: 18

Nathan Whitehead
Nathan Whitehead

Reputation: 2012

It shouldn't do any harm to run qt-faststart more than once, it will be a no-op the second time. So the easiest solution is to always run qt-faststart.

For more precise control, I would use the Python translation of qt-faststart: https://github.com/danielgtaylor/qtfaststart

It has functions that examine the atoms in an MP4 file, it shouldn't be too hard to use them to determine whether they need to be reordered.

Upvotes: 8

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