2018-12-20 14:22 GMT+01:00, Robert Krüger <[email protected]>: > On Tue, Dec 18, 2018 at 11:40 PM Carl Eugen Hoyos <[email protected]> > wrote: > >> 2018-12-18 21:49 GMT+01:00, Robert Krüger <[email protected]>: >> > On Fri, Dec 14, 2018 at 5:28 PM Carl Eugen Hoyos <[email protected]> >> wrote: >> > >> >> 2018-12-14 17:19 GMT+01:00, Robert Krüger <[email protected]>: >> >> > On Fri, Dec 14, 2018 at 3:03 AM Carl Eugen Hoyos <[email protected]> >> >> wrote: >> >> > >> >> >> 2018-12-13 17:10 GMT+01:00, Robert Krüger <[email protected] >> >: >> >> >> >> >> >> > is there a way to get the exact duration of a raw mpeg1 file using >> >> >> > the >> >> >> > ffmpeg command line? For testing I created a 30 minute test file >> >> >> > using >> >> >> > ffmpeg (using -c:v mpeg1video -f mpeg1video), then verified the >> >> duration >> >> >> > using VLC and mediainfo and it is indeed exactly 30 minutes long >> but >> >> >> > ffmpeg -i shows the file's duration as 00:00:04.98 after >> >> >> > displaying >> >> this >> >> >> > warning: >> >> >> > >> >> >> > [mpegvideo @ 0x7fe212806000] Estimating duration from bitrate, >> >> >> > this >> >> >> > may be inaccurate >> >> >> > >> >> >> > Are there command line parameters to make it compute the exact >> >> >> > size or is this a design or implementation limitation? >> >> >> >> >> >> Just the mpeg specification;-) >> >> >> >> >> > Yes, sure, having to count packets/frames is unavoidable for some >> >> formats. >> >> > My question is rather whether ffmpeg's (or rather libavformat's) >> >> > duration >> >> > computation code can be made to do this internally without these >> >> > workarounds. >> >> > >> >> >> $ ffmpeg -i input -c copy -f null - >> >> > >> >> > Thanks for the command line. >> >> > >> >> > Just a comparison: This approach gives me the duration information >> for a >> >> > 180 minute file in 1.8 seconds while mediainfo does it in 0.25 >> >> > seconds >> >> >> >> (Does your input have timestamp discontinuities? You could try to >> >> concatenate a few parts - or cut away something - from the input file.) >> >> >> > >> > Very unlikely since I generated the sample using an ffmpeg command line >> > using testsrc. >> >> But you should test with a file with timestamp discontinuities to >> test your claim that it can be done faster than with FFmpeg. > > I begin to understand. You are saying that it is possible that Mediainfo is > more or less "cheating" to obtain its results.
I meant that it is possible to calculate a duration in an mpeg stream by looking at the first and the last timestamp, MPlayer does it iirc. Carl Eugen _______________________________________________ ffmpeg-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
