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• Determine timestamp in mpg video of KLV streams

  22 février 2024, par Joshua Levoy

  I'm currently working with MISP compliant klv data containing mpg videos. I'm able to find the streams containing this data with ffmpeg using the following command

  


  `ffmpeg -v 0 -ss 0 -i "Day Flight.mpg" -map 0:1 -f framecrc  -`


  


  By varying the -ss argument I am able to select for different klv streams by excluding parts of the video, which leads me to believe that ffmpeg is capable of determining how far into the video these klv streams are. I'd very much be interested in finding these timestams of the KLV streams, such that I can create a process by which a misp compliant mpg video can be clipped into smaller segments, for which its relevant MISP-compliant klv data will be preserved.

  


  Is there a way to get ffmpeg to show me the timestamps where these KLV streams begin, and if not, does anyone know of any better approach to determining the position within the video of these klv streams ?

  


  you can obtain the mpg video file containing mpg data that I am using here https://samples.ffmpeg.org/MPEG2/mpegts-klv/Day%20Flight.mpg

  


  Currently I have run the line laid out above and receive the following output :

  


     #software: Lavf58.29.100 #tb 0: 1/90000 #media_type 0: data #codec_id 0: klv 0,          0,          0,        0,      163, 0xc7572adf, S=1,        1, 0x00bd00bd 0,          0,          0,        0,      163, 0xeddd2774, S=1,        1, 0x00bd00bd 0,          0,          0,        0,      163, 0x5c8d29b0, S=1,        1, 0x00bd00bd 0,          0,          0,        0,      163, 0xb7c428f5, S=1,        1, 0x00bd00bd 0,          0,          0,        0,      163, 0x3c3d28a5, S=1,        1, 0x00bd00bd 0,          0,          0,        0,      162, 0x5cdd2898, S=1,        1, 0x00bd00bd

  


  which is useful for determining there are KLV packets within the video but provides me very little in the way of the timestamp where they are relevant. I have other methods of extracting and decoding these KLV values at these locations, but what I'm interested in specifically, is knowing as close as possible the exact timestamps that the KLV streams are referring to within the 3 minute and 20 second video.

  


• How can I determine video rotation/orientation in PHP/FFMPEG/PhoneGap ?

  15 août 2024, par SomethingOn

  Once I upload videos to my server I'm creating a screencap using FFMPEG. Problem is, if the user takes a video in portrait mode the screencap is rotated 90º. The ridiculous things is that PhoneGap and FFMEG-php and FFMPEG don't seem to offer a mechanism for reading the video rotation/orientation value.

  



  I found another library called mediainfo that will provide the info, but not in an easy to read/digest manner and I'm trying to avoid having to use another library.

  



  Am I wrong about PhoneGap/FFMPEG ? Is there a direct way to determine video orienation ?

  



  ---

  



  Here's my solution as a PHP function :

  



  function get_video_orientation($video_path) {
    $cmd = FFMPEG_PATH . "ffprobe " . $video_path . " -show_streams 2>/dev/null";
    $result = shell_exec($cmd);

    $orientation = 0;
    if(strpos($result, 'TAG:rotate') !== FALSE) {
        $result = explode("\n", $result);
        foreach($result as $line) {
            if(strpos($line, 'TAG:rotate') !== FALSE) {
                $stream_info = explode("=", $line);
                $orientation = $stream_info[1];
            }
        }
    }

    return $orientation;
}


  


• Determine which decoders/demuxers/parsers ffmpeg needs to successfully consume file

  10 octobre 2024, par rschristian

  I'm trying to custom compile a build of ffmpeg.wasm as the prebuilt, "support everything" is a tad hefty at 35mb. This base build (as well as standard ffmpeg, running on my desktop) works perfectly fine for the provided file, however, so I do have something I can work against.

  


  My issue is that I'm a bit stuck on figuring out what precisely I need to support the provided file, the correct combination of decoders, demuxers, parsers, etc., and the encoders, muxers I'll need to use to convert it to my desired output.

  


  I'm sure I can brute force this with time, but is there a way of having ffmpeg report precisely which combination it's using when running against a file ? I've tried -report but it doesn't seem to contain this information, really it contains no more useful codex information than the standard output log as far as I can tell.

  


  For example, I can see the current file I'm testing with (foo.m4s) is h264 video and aac audio, so I tried the following flags based on what I've been able to find online and by looking through the list of muxers :

  


  --enable-decoder=aac,h264
--enable-demuxer=aac,h264
--enable-parser=aac,h264


  


  However, this results in the following error :

  


  foo.m4s: Invalid data found when processing input


  


  So it seems like it's not quite the correct list.

  


  Is there any good way to debug this ? Some way of having ffmpeg itself report exactly what I'll need set to handle this conversion using my own compilation ? As the goal is a minimum build, adding the kitchen sink and slowly reducing over time will obviously be super time consuming, so I'd like to avoid it if at all possible.

  


  ---

  


  Edit : Trial and error got me down to this, though I don't quite understand it (and the question still stands as I could reasonably need to handle other files in the future) :

  


  --enable-demuxer=aac,mov
--enable-parser=aac


  


  mov for some reason ended up being the fix ? The first line of ffmpeg's output was Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'foo.m4s', and so I simply grabbed those one-by-one and sure enough mov worked, despite the video having h264. Would love if someone could explain this too.