Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Mikhail V]

On 8 October 2016 at 00:31, Carl Eugen Hoyos  wrote:
> 2016-10-08 0:01 GMT+02:00 Mikhail V :
>> BTW after that manipulations a fair question arizes: why
>> ffmpeg does not support something like:
>>  "... -f image2 -i filelist.txt output"
>
> (This command tries to read a frame / imagefile called filelist.txt)
> It does, it is called -f concat and is just an alternative of your
> python script.
>
> Carl Eugen

Hi again.
Since you say that "-f concat" should work same as -f image2 to create
video from images,
probably you can pour some light on what I am doing wrong then.
Note that ideally I need an MOV file because Sony Vegas cannot open MXF files
 for some reason so MOV container is preferred.
So I have a file "concat.txt" in my case it holds following data:

file 'frame0001'
file 'frame0003'
file 'frame0005'
file 'frame0007'
file 'frame0009'
file 'frame0011'


So it is simply a list of odd frames  generated by my script.
Now to create a MXF I use this command:

$ffmpeg -f concat -r 25 -i concat.txt -vcodec copy out.mxf

Which is probably not correct?  but I don't know exact right command.
The result seems correct BUT ffmpeg spits out errors on each frame
(here is only last part of the output):



[mxf @ 028f2461b200] Application provided invalid, non
monotonically increasing dts to muxer in stream 0: 1 >= 0
Last message repeated 62 times
frame=  813 fps= 46 q=-1.0 size=  365042kB time=00:00:00.08
bitrate=37380251.6kbits/s
[mxf @ 028f2461b200] Application provided invalid, non
monotonically increasing dts to muxer in stream 0: 1 >= 0
Last message repeated 140 times
frame=  954 fps= 52 q=-1.0 size=  428351kB time=00:00:00.08
bitrate=43863093.2kbits/s
[mxf @ 028f2461b200] Application provided invalid, non
monotonically increasing dts to muxer in stream 0: 1 >= 0
Last message repeated 138 times
frame= 1093 fps= 58 q=-1.0 size=  490762kB time=00:00:00.08
bitrate=50253979.6kbits/s
[mxf @ 028f2461b200] Application provided invalid, non
monotonically increasing dts to muxer in stream 0: 1 >= 0
Last message repeated 142 times
frame= 1236 fps= 64 q=-1.0 size=  554969kB time=00:00:00.08
bitrate=56828776.4kbits/s
 [mxf @ 028f2461b200] Application provided invalid, non
monotonically increasing dts to muxer in stream 0: 1 >= 0
Last message repeated 142 times
frame= 1379 fps= 70 q=-1.0 size=  619176kB time=00:00:00.08
bitrate=63403573.2kbits/s
 [mxf @ 028f2461b200] Application provided invalid, non
monotonically increasing dts to muxer in stream 0: 1 >= 0
Last message repeated 120 times
frame= 1500 fps= 74 q=-1.0 Lsize=  673506kB time=00:00:00.08
bitrate=68966967.7kbits/s speed=0.00395x
video:672000kB audio:0kB subtitle:0kB other streams:0kB global
headers:0kB muxing overhead: 0.224039%


As said the resulting file is correct, but what does these errors mean
I am not sure.
Anyway if I use -f image2 to generate a same video no errors appear -
how is that?
What is correct command then for concat if I am doing it wrong?

Now the same command for mov container. MOV is also valid for DNxHD codec and
 actually is preferred in my case since MXF files cannot be opened by
Sony Vegas.

$ffmpeg -f concat -r 25 -i concat.txt -vcodec copy out.mxf

And the output (last part of it, since it also spits out errors on each frame):

[mov @ 014afd95b200] Non-monotonous DTS in output stream 0:0;
previous: 1258, current: 0; changing to 1259. This may result in
incorrect timestamps in the output file.
[mov @ 014afd95b200] Non-monotonous DTS in output stream 0:0;
previous: 1259, current: 512; changing to 1260. This may result in
incorrect timestamps in the output file.
[mov,mp4,m4a,3gp,3g2,mj2 @ 014aff2a0420] moov atom not found
[concat @ 014afd956640] Impossible to open 'out.mov'
concat.txt: Invalid data found when processing input
frame=  750 fps= 43 q=-1.0 Lsize=  336002kB time=00:00:00.13
bitrate=19882772.1kbits/s speed=0.00788x
video:336000kB audio:0kB subtitle:0kB other streams:0kB global
headers:0kB muxing overhead: 0.000698%

In this case it produces a file but it is _incorrect_
See FFPROBE for mov file - fps is nonsense:

$ffprobe out.mov

ffprobe version N-79107-g30d1213 Copyright (c) 2007-2016 the FFmpeg developers
  built with gcc 5.3.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads
--enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r
--enable-gnutls --enable-iconv --enable-libass --enable-libbluray
--enable-libbs2b --enable-libcaca --enable-libdcadec
--enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc
--enable-libmodplug --enable-libmfx --enable-libmp3lame
--enable-libopencore-amrnb --enable-libopencore-amrwb
--enable-libopenjpeg --enable-libopus --enable-librtmp
--enable-libschroedinger --enable-libsnappy --enable-libsoxr
--enable-libspeex --enable-libtheora --enable-libtwolame
--enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis
--enable-libvpx 

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Carl Eugen Hoyos]

2016-10-08 0:01 GMT+02:00 Mikhail V :
> BTW after that manipulations a fair question arizes: why
> ffmpeg does not support something like:
>  "... -f image2 -i filelist.txt output"

(This command tries to read a frame / imagefile called filelist.txt)
It does, it is called -f concat and is just an alternative of your
python script.

Carl Eugen
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Mikhail V]

> You can do:
> $ ffmpeg -i input -vcodec copy -f image2 frame%4d
>
> Now make symbolic links to every second frame but
> with sequential numbers (Don't ask me how).
> $ ffmpeg -f image2 -vcodec dnxhd -i linked_frames%4d -vcodec copy out.mxf
> (25fps is the default for the image2 demuxer, use -framerate to change it)

Great, this worked for me. I don't know symlinks yet however so I have just
deleted every second frame with a python script and  then
ran that command - worked fine, a video file produces correctly.

> Or simply concatenate the frames you like with "cat" and do:
> $ ffmpeg -i concatenated_file -vcodec copy out.mxf

Well with concatenate I am also not very familiar, but I will look
in Moritz' solution. I tried to pass a list with only filenames to concat
filter but that did not work, seems the list must contain time points as
in Moritz' solution to work at all.
BTW after that manipulations a fair question arizes: why
ffmpeg does not support something like:
 "... -f image2 -i filelist.txt output"
It would ease all those strange manipulations and would not
need symlinks or whatever.
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Carl Eugen Hoyos]

2016-10-07 14:06 GMT+02:00 Moritz Barsnick :
> On Fri, Oct 07, 2016 at 13:07:53 +0200, Carl Eugen Hoyos wrote:
>> 2016-10-06 17:34 GMT+02:00 Moritz Barsnick :
>> > $ ffmpeg -r 25 -f concat -i concatscript.txt -c:v copy output.mxf
>>
>> This scales very badly, no?
>
> It's just a proof of concept. :) It scales nicely (linearly? or is

I don't think so or at least I accept it to be magnitudes slower
than using the symlinks.

> seeking more expensive the deeper you seek?), and works
> assuming you have CFR input and output, and you know
> those rates, and ... , and ...
> ;-)
>
> It "scales" better then writing every frame to disk and selecting
> every second one by symlinking. That's 18 intermediate
> files plus 9 symlinks for one hour of video.

> Then I'd rather have ffmpeg seek into the input file 9 times.

But it actually opens the file 9 times;-(

Carl Eugen
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Marton Balint]

On Fri, 7 Oct 2016, Moritz Barsnick wrote:


On Fri, Oct 07, 2016 at 13:07:53 +0200, Carl Eugen Hoyos wrote:

2016-10-06 17:34 GMT+02:00 Moritz Barsnick :
> $ ffmpeg -r 25 -f concat -i concatscript.txt -c:v copy output.mxf

This scales very badly, no?


It's just a proof of concept. :) It scales nicely (linearly? or is
seeking more expensive the deeper you seek?), and works assuming you
have CFR input and output, and you know those rates, and ... , and ...
;-)


Scaling issues are probably caused by the fact that the concat demuxer 
reopens the file for each frame, instead of detecting that the next 
segment is referring to the same file as the previous one. Probably not 
too hard to improve the concat demuxer to detect such cases and avoid 
reopening the source.


Regards,
Marton
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Moritz Barsnick]

On Fri, Oct 07, 2016 at 13:07:53 +0200, Carl Eugen Hoyos wrote:
> 2016-10-06 17:34 GMT+02:00 Moritz Barsnick :
> > $ ffmpeg -r 25 -f concat -i concatscript.txt -c:v copy output.mxf
> 
> This scales very badly, no?

It's just a proof of concept. :) It scales nicely (linearly? or is
seeking more expensive the deeper you seek?), and works assuming you
have CFR input and output, and you know those rates, and ... , and ...
;-)

It "scales" better then writing every frame to disk and selecting every
second one by symlinking. That's 18 intermediate files plus 9
symlinks for one hour of video. Then I'd rather have ffmpeg seek into
the input file 9 times. But both basically suck. I still prefer
that "select" bitstream filter. ;-)

Moritz
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Carl Eugen Hoyos]

2016-10-06 17:34 GMT+02:00 Moritz Barsnick :
> $ ffmpeg -r 25 -f concat -i concatscript.txt -c:v copy output.mxf

This scales very badly, no?

Carl Eugen
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Moritz Barsnick]

On Thu, Oct 06, 2016 at 16:07:02 +0200, Moritz Barsnick wrote:
> I found the suggestion to use the concat demuxer with streamcopy very
> interesting. Assuming it can seek and cut precisely, that could work -
> again in theory. Let's experiment with that. :)

So, where are your results, everyone? ;-) Here are mine.

I created a 50 fps DNxHR MXF file. The testsrc2 filter/source kindly
puts the frame numbers onto each frame:

$ ffmpeg -f lavfi -i testsrc2=s=hd720:r=50 -c:v dnxhd -profile:v dnxhr_hq -t 3 
input.mxf

I created a concat script for these three seconds, to select every
second frame, which means stepping forward by 0.040 (two frames at 50
fps), for a duration of 0.020 (one frame):

$ perl -e 'print "ffconcat version 1.0\n\n"; my $t = 0; while ($t <= 3) { 
printf("file input.mxf\ninpoint %1.3f\nduration 0.020\noutpoint %1.3f\n\n", $t, 
$t + 0.020); $t += 0.040; }' > concatscript.txt

Then I used this concat demuxer script to do the actual extraction:

$ ffmpeg -r 25 -f concat -i concatscript.txt -c:v copy output.mxf

Visual inspection of the result shows me that every second frame was
extracted, at a resulting frame rate of 25 fps.

Verifying with the frashhash demuxer showed me that every second frame
is indeed identical:

$ ffmpeg -i input.mxf -c copy -f framehash input.mxf.hash
$ ffmpeg -i output.mxf -c copy -f framehash output.mxf.hash

Bingo! :-)

Still, a bitstream filter would be nifty. ;-)

Moritz
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Carl Eugen Hoyos]

2016-10-06 16:16 GMT+02:00 Mikhail V :

> I admit I am not fully getting your idea then.

Your original email (and subsequent ones) sounded as if you knew
exactly what has to be done, you were just asking if it is possible
without a little shell magic (I think it is not).

You can do:
$ ffmpeg -i input -vcodec copy -f image2 frame%4d

Now make symbolic links to every second frame but
with sequential numbers (Don't ask me how).
$ ffmpeg -f image2 -vcodec dnxhd -i linked_frames%4d -vcodec copy out.mxf
(25fps is the default for the image2 demuxer, use -framerate to change it)

Or simply concatenate the frames you like with "cat" and do:
$ ffmpeg -i concatenated_file -vcodec copy out.mxf

Carl Eugen
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Carl Eugen Hoyos]

2016-10-06 15:53 GMT+02:00 Marcelo Boufleur :
> I'm not sure that what Mikhail wants really exists. If I understand
> correctly, you want to retain original encoding and drop one frame every
> two frames.
>
> If this would be possible, you would have to work at the DNxHD inner level,
> identify each frame start/end (by headers), bit-stream copy whichever
> frames you would need,

Fortunately, FFmpeg does all this for you: We call it "parsing" and it
is necessary for many (general) use-cases.

> and then re-generate the DNxHD layer and headers to
> reflect all the changes you have made.

No such header exists for dnxhd, just for mxf.

Carl Eugen
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Mikhail V]

On 6 October 2016 at 10:07, Carl Eugen Hoyos  wrote:
> 2016-10-05 23:08 GMT+02:00 Mikhail V :
>> On 5 October 2016 at 19:55, Carl Eugen Hoyos  wrote:
>>> 2016-10-05 15:45 GMT+02:00 Mikhail V :
>>>
 Is it possible that ffmpeg cannot do this without re-encoding?
>>>
>>> You can export single frames and delete half of them using a
>>> shell script.
>
>> Sure I can :) Also I can just directly recode it in 25 fps in any codec.
>> So I suppose the answer is - I can't do it without re-encode.
>
> If you want to drop every second frame without re-encoding at
> all, you can export all frames as single frames and use a shell
> script to drop half of them.

I admit I am not fully getting your idea then. I want the output as
same video file.
If I export as images then it is just a folder with images. Yes they
will be not changed,
but if I want them back in a DNxHD video file, how can I guarantee
that the information
will be not changed due to compression? Do you mean this is possible somehow to
put the images back in video file without touching the image information?
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Moritz Barsnick]

On Thu, Oct 06, 2016 at 10:53:14 -0300, Marcelo Boufleur wrote:
> I'm not sure that what Mikhail wants really exists. If I understand
> correctly, you want to retain original encoding and drop one frame every
> two frames.

I understand the same thing. (Carl Eugen was concentrating on Mikhail's "not
re-encoding" wording, which can of course be achieved by just decoding.
;-)) Keep every second frames without decoding them, but re-assembling
them to a valid MXF.

> If this would be possible, you would have to work at the DNxHD inner level,
> identify each frame start/end (by headers), bit-stream copy whichever
> frames you would need, and then re-generate the DNxHD layer and headers to
> reflect all the changes you have made.

Exactly. Since you don't want to decode (which implies re-encoding),
this would be with "-c:v copy" and would effectively be a bitstream
filter. I'm not aware that any such filter exists (and whether the
ffmpeg devs would even consider accepting integrating such a bsf). It
pure theory, this *could* even be done for more codecs than just DNxHD.

> I may be wrong, but I believe with current FFmpeg implementation you can
> only work either with stream copy (if you don't want to change encoding,
> nor frame rate, which defies his purpose), or use the previous suggestions
> to cut framerate by half, which implies on re-encoding (which again, defies
> his purpose).

I found the suggestion to use the concat demuxer with streamcopy very
interesting. Assuming it can seek and cut precisely, that could work -
again in theory. Let's experiment with that. :)

Moritz
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Marcelo Boufleur]

I'm not sure that what Mikhail wants really exists. If I understand
correctly, you want to retain original encoding and drop one frame every
two frames.

If this would be possible, you would have to work at the DNxHD inner level,
identify each frame start/end (by headers), bit-stream copy whichever
frames you would need, and then re-generate the DNxHD layer and headers to
reflect all the changes you have made.

I may be wrong, but I believe with current FFmpeg implementation you can
only work either with stream copy (if you don't want to change encoding,
nor frame rate, which defies his purpose), or use the previous suggestions
to cut framerate by half, which implies on re-encoding (which again, defies
his purpose).
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Carl Eugen Hoyos]

2016-10-05 23:08 GMT+02:00 Mikhail V :
> On 5 October 2016 at 19:55, Carl Eugen Hoyos  wrote:
>> 2016-10-05 15:45 GMT+02:00 Mikhail V :
>>
>>> Is it possible that ffmpeg cannot do this without re-encoding?
>>
>> You can export single frames and delete half of them using a
>> shell script.

> Sure I can :) Also I can just directly recode it in 25 fps in any codec.
> So I suppose the answer is - I can't do it without re-encode.

If you want to drop every second frame without re-encoding at
all, you can export all frames as single frames and use a shell
script to drop half of them.

Carl Eugen
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Marton Balint]

On Wed, 5 Oct 2016, Mikhail V wrote:


On 5 October 2016 at 19:55, Carl Eugen Hoyos  wrote:

2016-10-05 15:45 GMT+02:00 Mikhail V :


Is it possible that ffmpeg cannot do this without re-encoding?


You can export single frames and delete half of them using a
shell script.

Carl Eugen


Sure I can :) Also I can just directly recode it in 25 fps in any codec.
So I suppose the answer is - I can't do it without re-encode.
I was just wondering why there is no such function for intraframe codecs,
would be very handy in my opinion.


You may try generating an ffconcat file which seeks to every second frame, 
then force the halved frame rate for it, finally mux this with the 
original audio using streamcopy. With a little luck, this should work.


Regards,
Marton
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Mikhail V]

On 5 October 2016 at 19:55, Carl Eugen Hoyos  wrote:
> 2016-10-05 15:45 GMT+02:00 Mikhail V :
>
>> Is it possible that ffmpeg cannot do this without re-encoding?
>
> You can export single frames and delete half of them using a
> shell script.
>
> Carl Eugen

Sure I can :) Also I can just directly recode it in 25 fps in any codec.
So I suppose the answer is - I can't do it without re-encode.
I was just wondering why there is no such function for intraframe codecs,
would be very handy in my opinion.
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Mikhail V]

On 5 October 2016 at 18:06, Erik Dobberkau  wrote:
>> Hello,
>>
>> I have a camera recording which is an MXF file and the codec is DNxHD
>> I suppose it is a single-frame codec so literally it is a container of
>> images which are independently stored in the file.
>> Recordings are taken at 50 fps progressive.
>
>
> Hi Michail,
>
> this is a TV standard, 720p50. Nothing exotic.
>
>
>> Now what I want is to extract only half of the frames, so that it becomes
>> 25 fps
>
>
> Why would you want to do that?
> You're getting standard-incompliant video. In other words: This is wrong.


You are right, but what is standard depend on situation, currently the
only working
mode for me is 25 progressive. I know 50 fps would be better of course,
but it does not depend on me but the prescriptions from the broadcaster.
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Carl Eugen Hoyos]

2016-10-05 15:45 GMT+02:00 Mikhail V :

> Is it possible that ffmpeg cannot do this without re-encoding?

You can export single frames and delete half of them using a
shell script.

Carl Eugen
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Erik Dobberkau]

> Hello,
>
> I have a camera recording which is an MXF file and the codec is DNxHD
> I suppose it is a single-frame codec so literally it is a container of
> images which are independently stored in the file.
> Recordings are taken at 50 fps progressive.


Hi Michail,

this is a TV standard, 720p50. Nothing exotic.


> Now what I want is to extract only half of the frames, so that it becomes
> 25 fps


Why would you want to do that?
You're getting standard-incompliant video. In other words: This is wrong.


> Note that I need to do it _without re-encoding_ for two reasons:
> 1. Conversion must be as fast as possible, files can be really huge
> 2. No changes to original information should occur
>
> Theoretically this is an elementary operation, it should just take
> every second frame from source and write to output
> leaving everything else as is.
> I have tried several options whith "-r ..." and added "-c:v copy"
> These commands I have tried:
>
> ffmpeg -i Capture0006V_720p.mxf -r 25 -c:v copy out1.mxf
> ffmpeg -r 50 -i Capture0006V_720p.mxf -r 25 -c:v copy out1.mxf
> ffmpeg -r 2 -i Capture0006V_720p.mxf -r 1 -c:v copy out1.mxf
>
> But they all produce again 50 fps video, so I suppose stream copy just
> ignores all "-r" options so I don't know what can I do to achieve
> what I want. I have searched a lot, so I've registered here
> hoping for solution.
>
> Is it possible that ffmpeg cannot do this without re-encoding?
> If no, how can one do this?
> Thanks in advance.
>

Stream Copy does that... it copies streams.
Dropping every second frame will destroy motion smoothness thus ruin your
video. But you can do that with another filter.

Erik
___
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-user

To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".