[FFmpeg-user] Get exact duration of an mpeg1 file
Carl Eugen Hoyos
ceffmpeg at gmail.com
Fri Dec 14 18:28:38 EET 2018
2018-12-14 17:19 GMT+01:00, Robert Krüger <krueger at lesspain.software>:
> On Fri, Dec 14, 2018 at 3:03 AM Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
>> 2018-12-13 17:10 GMT+01:00, Robert Krüger <krueger at lesspain.software>:
>> > 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
>> $ 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.)
> (being exact while ffmpeg is a few frames off, but that's a different
> topic), so there must be a faster way to implement it.
Patch probably welcome.
> Tested with a number
> of different files with identical results in principle.
> What keeps confusing me is that analyzeduration and probesize really seem
> to be the parameters that should address the behaviour
No, you misunderstand "analyzeduration", it does not analyze the
duration of the input but specifies the duration that should be used
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