How do I get the play length of an ogg file without downloading the whole file? I know this is possible because both the HTML5  tag and VLC can show the entire play length immediately after loading the URL, without downloading the entire file.
Is there a header or something I can read. Maybe even the bitrate, which I can divide by the file size to get an approximate play length?
This is just not possible without download the data itself. You could specify the related information as part of the S3 metadata of the related key. So could write to introspect the metadata before actually downloading the data.
Getting the length of a ogg track from s3 without downloading the whole file