[FFmpeg-user] Problem: extracted alpha plane from a grayscale PNG is shifted by 1 pixel to the left

[Mikhail V]

I have a strange problem with extracting alpha plane from an grayscale
PNG with alpha channel.
So I have an image with alpha in it and use this command:

ffmpeg -i 1-open-patch.png  -vf alphaextract   -pix_fmt gray  testgray_alpha.png
or
ffmpeg -i 1-open-patch.png  -vf alphaextract   testgray_alpha.png
(wich works same way I think)

Problem:  the output alpha plane is shifted 1 pixel to the left. The
data is ok - but the position is 1 pixel shifted.
The problem appears only with ya8 pixel format. If I use same but RGBa
image the output plane is correctly positioned.

Windows 10 latest build

Console  output:

ffmpeg -i 1-open-patch.png  -vf alphaextract  testgray_alpha.png
ffmpeg version N-93532-g772c73e61f Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 8.2.1 (GCC) 20190212
  configuration: --enable-gpl --enable-version3 --enable-sdl2
--enable-fontconfig --enable-gnutls --enable-iconv --enable-libass
--enable-libdav1d --enable-libbluray --enable-libfreetype
--enable-libmp3lame --enable-libopencore-amrnb
--enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus
--enable-libshine --enable-libsnappy --enable-libsoxr
--enable-libtheora --enable-libtwolame --enable-libvpx
--enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265
--enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib
--enable-gmp --enable-libvidstab --enable-libvorbis
--enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex
--enable-libxvid --enable-libaom --enable-libmfx --enable-amf
--enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc
--enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt
  libavutil  56. 26.100 / 56. 26.100
  libavcodec 58. 48.101 / 58. 48.101
  libavformat58. 26.101 / 58. 26.101
  libavdevice58.  7.100 / 58.  7.100
  libavfilter 7. 48.100 /  7. 48.100
  libswscale  5.  4.100 /  5.  4.100
  libswresample   3.  4.100 /  3.  4.100
  libpostproc55.  4.100 / 55.  4.100
Input #0, png_pipe, from '1-open-patch.png':
  Duration: N/A, bitrate: N/A
Stream #0:0: Video: png, ya8(pc), 800x600 [SAR 2835:2835 DAR 4:3],
25 tbr, 25 tbn, 25 tbc
File 'testgray_alpha.png' already exists. Overwrite ? [y/N] y
Stream mapping:
  Stream #0:0 -> #0:0 (png (native) -> png (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'testgray_alpha.png':
  Metadata:
encoder : Lavf58.26.101
Stream #0:0: Video: png, gray, 800x600 [SAR 2835:2835 DAR 4:3],
q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc
Metadata:
  encoder : Lavc58.48.101 png
frame=1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A speed=0.853x
video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: unknown



Mikhail
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[FFmpeg-user] FFmpeg website (ffmpeg.org)

[Mikhail V]

Hi,

[Offtopic]

I am using the online documentation a lot, especially
this page https://ffmpeg.org/ffmpeg-filters.html

Frankly, I find the site quite hard to read.
(IMO, so please don't take as offense)

I have published a userstyle for Firefox (with Stylish plugin)
that adresses the issues and tends to make it more
reader-friendly, i.e. basically it is a remake of the css of
ffmpeg.org, but only for most significant styles.
Link:
https://userstyles.org/styles/153930/greengray-ffmpeg-org
(or just search for 'ffmpeg' on userstyles.org)

To use it, you must install the Stylish plugin.
I have made a windows/firefox only version because I don't
have linux now at hand.

@maintainers: you might forward this to the site maintainers
so they might borrow the design for the actual website if
there is a wish.


Regards,
Mikhail
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[FFmpeg-user] feature proposal - avoid overwriting the input file

[Mikhail V]

James Girotti wrote:

> On Tue, Oct 10, 2017 at 4:40 PM, Mikhail V  wrote:
>
> > Currently it is possible to delete the input file if I specify same
> > filename in output,
> > for example:
> >
> > ffmpeg -y -i input input
> >
>
> Aren't you specifying that with '-y' you want to "overwrite output file
> without asking"

Sure, I am. But anybody can miss the typo, and its not so easy to
notice in console or text editor, its just two chars
in a pile of chars.

>
>
> > or simply:
> > ffmpeg -i input input
> > (this will promt y/n)
> >
>
> I believe this is the default behavior for any output file that is present
> whether it matches input or not (in my example both foo.mkv and bar.mkv
> file present):

I see your point, yes I can do it with any existing file so there is no
fool-proof for general case.
But you know, if I delete some wrong output file, then still I have some
consolation because I don't lose the input file :)
Losing some random output file is not so bad usually from my
experience because I probably notice somthing gone wrong within short time
 and sources for that file still (hopefully) exist.


> > Was quite funny actually :) Funniest thing that I could not recover the
> > file
> > because it is same name.
> >
>
> That reminds me of when I accidentally did 'rm -rf /*'

Yeh, wrong batch renaming can cause  a lot of interesting
situations.

> >
> > So, it would be nice if ffmpeg compare the output path with all input paths
> > and exit with an error.
> >
>
> Is it possible for you to run your command without '-y' or if you're using
> a script, then to compare your input and output before passing them to
> ffmpeg?

Actually this happened to me without '-y'. That time I have
just reflexively typed 'y' and enter when prompted [Y/N].
And I can understand because this reflex of mine was trained by
doing a lot of trial-and error encodings in the past. In batch scripts
I never use '-y'
options.
Probability of such accident raises when copy-pasting file paths
from a file manager into ready full command line strings.

And what I am wondering, what can be really *against* such
feature.
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[FFmpeg-user] A spelling error in a warning message?

[Mikhail V]

Sometimes I get a warning:

> Warning: data is not aligned! This can lead to a speedloss

"Speedloss" should be "speed loss" I suppose?



Mikhail
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[FFmpeg-user] Pixel average color filter

[Mikhail V]

Dear ffmpeg team,

I need a filter which fills output frame with average color of input.
Currently I need it to do row-wise average.
Pseudo-code:

- take first pixel row
- calculate average color in this row and fill output row with this color
- take next row
- repeat same operation
...
and so for all input frame rows


So the output frame will be filled with the average color of input
frame row-wise.

Is there such filter or something similar so I can get similar results?


Regards,
Mikhail V
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Re: [FFmpeg-user] tools for viewing frames and results

[Mikhail V]

On 10/11/2016 2:24 PM, Mikhail V wrote:

On 10/9/2016 12:24 AM, Xen wrote:
Is there any way in Linux to obtain an accurate frame/time number 
through a GUI that can be used with ffmpeg?


I know Avidemux hardly works at all, VLC will not reliably show frames.

Pitivi is not an option, I haven't tried Kdenlive because it crashed 
the first time I used it.


Haven't attempted OpenShot or Cinerella and "DragonPlayer" is too 
worthless to exist.


What is a good tool to view results after you've created a video? 
Because VLC closes its window and constantly resizes stuff it is not 
very suitable.


GMplayer in Debian doesn't work. (Kubuntu).


I suppose you just want a decent player with frame-by-frame navigation.
I use MPC-HC player (https://mpc-hc.org/ ).
It is much better than VLC for this purpose, you can navigate
frame by frame and show time with milliseconds, and even set custom
keyboard shortcuts. If you want to see exact frame number I don't think
there is such a player.



Sorry, didn't know this Windows only player, just seen it on their site.
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Re: [FFmpeg-user] tools for viewing frames and results

[Mikhail V]

On 10/9/2016 12:24 AM, Xen wrote:
Is there any way in Linux to obtain an accurate frame/time number 
through a GUI that can be used with ffmpeg?


I know Avidemux hardly works at all, VLC will not reliably show frames.

Pitivi is not an option, I haven't tried Kdenlive because it crashed 
the first time I used it.


Haven't attempted OpenShot or Cinerella and "DragonPlayer" is too 
worthless to exist.


What is a good tool to view results after you've created a video? 
Because VLC closes its window and constantly resizes stuff it is not 
very suitable.


GMplayer in Debian doesn't work. (Kubuntu).


I suppose you just want a decent player with frame-by-frame navigation.
I use MPC-HC player (https://mpc-hc.org/ ).
It is much better than VLC for this purpose, you can navigate
frame by frame and show time with milliseconds, and even set custom
keyboard shortcuts. If you want to see exact frame number I don't think
there is such a player.


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

[Mikhail V]

On 8 October 2016 at 00:31, Carl Eugen Hoyos <ceffm...@gmail.com> wrote:
> 2016-10-08 0:01 GMT+02:00 Mikhail V <mikhail...@gmail.com>:
>> 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

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

[Mikhail V]

On 6 October 2016 at 10:07, Carl Eugen Hoyos <ceffm...@gmail.com> wrote:
> 2016-10-05 23:08 GMT+02:00 Mikhail V <mikhail...@gmail.com>:
>> On 5 October 2016 at 19:55, Carl Eugen Hoyos <ceffm...@gmail.com> wrote:
>>> 2016-10-05 15:45 GMT+02:00 Mikhail V <mikhail...@gmail.com>:
>>>
>>>> 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?
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Re: [FFmpeg-user] Selecting/dropping frames without re-encoding

[Mikhail V]

On 5 October 2016 at 19:55, Carl Eugen Hoyos <ceffm...@gmail.com> wrote:
> 2016-10-05 15:45 GMT+02:00 Mikhail V <mikhail...@gmail.com>:
>
>> 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.
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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.
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[FFmpeg-user] Selecting/dropping frames without re-encoding

[Mikhail V]

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