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Old February 13th, 2010, 11:53 AM   #1
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Join Date: Mar 2005
Posts: 13
changing the frame rate of mov file?

we're capturing large images with an industrial camera used a lot for astronomical or
medical imaging. the images are 2048x1536. they capture directly to an avi file. the
software sets the file's frame rate at 10fps because that is the stream rate from the
camera. we are, however, not capturing the entire stream. we are capturing triggered
images, as in timelapse. we are also editing in a 24p environment and want our files to
match that with a frame rate of 24fps. we are editing on final cut.

i've tried using avifrate to change the files' frame rate and it works fine in windows.
the files are not correctly read at the new rate on the mac by qt player or final cut,
though. they both see the original 10fps rate. it doesn't appear to be an os level issue as
mpeg streamclip sees the new 24fps rate on the mac.

i tried making a ref movie and opening it in dumpster to view and edit the mov file
header info but have no idea, at this point, what to change. the relevant info seems
to be:

mvhd/timeScale 600
mvhd/duration 408000

edts/elst/Track Dur 408000
edts/elst/Media Rate 1.0

mdia/mdhd/timeScale 600
mdia/mdhd/duration 408000

mdia/minf/stbl/stts/sampCnt 6800
mdia/minf/stbl/stts/sampDur 60

the test file here has 6800 frames in it. it should run about 00:04:43:00. it currently
displays in qt player as 10fps with a duration of, something like, 00:11:20:00. i have
not found a combination of changes i could make to the info here that yields
24fps with the correct media length, data rate, and running time.

i'm posting here because i found a similar post here, although, it did not address
my issue closely enough to get me past this problem. seems like when i change one
thing, two or three change, and in differing ways. if i make a series of changes, it
might not do anything at all. very confusing.

can anyone here offer a formula as to how qt derives such info? i will have a lot of
this to do and it will save huge amounts of time to be able to make the necessary
changes in this manner instead of rerendering the files. many will be 400+gb.

George Lockwood is offline   Reply With Quote
Old February 17th, 2010, 02:24 PM   #2
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Join Date: Mar 2005
Posts: 13
ok. so, here's the solution. came from jan e. schotsman, maker of jes
deinterlacer. great utility. everyone should have it if you're on a mac.

make a qt ref movie from the avi.
open the ref movie in dumpster.
there are four fields to edit for duration here.
there is one other for 'sampDur'.

under 'trak--->mdia--->minf--->stbl--->stts' you'll find:


sampCnt is the number of frames in the file.
sampDur is fps. mine says 60, which corresponds to 10fps.

per jan's fix, i changed that to 25, which corresponds to 24fps.
you'll notice that 24fps is 10fps x 2.4 and that 25 = 60 / 2.4.

now, we use a formula:

sampCnt x sampDur

to derive a number for duration.

the file i'm looking at now has a samCnt of 17374.

17374 x 60 = 1042440
17374 x 25 = 434350

with these number, we now look for four fields containing the
original value of 1042440. they are:

'trak--->edts--->elst--->Track Dur'

each of these fields should contain the value 1042440.
change that to 434350.

make sure to click in another field after you make your last
change so the value will be retained. then save.

that's it. change five text fields and the file now opens
as a 24fps file with the correct durations. in my case, making
these five text entries (takes a minute or two), saved a three
to four hour transcode. and, i have to do this dozens of times
over saving, probably, hundreds of wasted hours.

thanks to jan!

these are simple files. in my case, picture only. i can imagine
there might be additional issues with files containing audio or
additional tracks.
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