Re: [FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

I'm not really sure why, but I got it to work with the following cmd... 
Thanks for your patience!


./shm | ffmpeg -f rawvideo -pixel_format bgr32 -video_size 1274x541 -framerate 
30 -i - out.mp4

On Sat, 3 Sep 2016, Joshua Grauman wrote:

Sorry for another question, but I'm having a hard time figuring out why this 
doesn't work. I've written a program to output raw image data (32-bit rgba), 
frame after frame. I'm trying a test to encode it to mp4, but this command 
says:


./shm | ffmpeg -f image2 -r 30 -s 1274x541 -pix_fmt rgb32 -vcodec rawvideo -i 
- out.mp4


Could find no file with path 'pipe:' and index in the range 0-4
pipe:: No such file or directory

What am I doing wrong?

Thanks!

Josh


On Fri, 2 Sep 2016, Joshua Grauman wrote:


 I've been looking for a way to screencast an app with alpha, but I haven't
 found one yet (but if someone knows of one, I'd love it). So I'm working
 on modifying my app to generate png's at 30 frames per second.

 Josh

>   2016-09-02 7:29 GMT+02:00 Joshua Grauman :
> >   I have another different, but related question. What format would you
> >   suggest for storing my screencast in? The resulting video is going to 
> >   be

> >   1080p30 and it needs to have an alpha channel
> 
>   Which screencast technology allows to record an alpha channel?

>   mpng should be best for screencasts, some people like utvideo.
> 
>   Carl Eugen

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Re: [FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

Sorry for another question, but I'm having a hard time figuring out why 
this doesn't work. I've written a program to output raw image data 
(32-bit rgba), frame after frame. I'm trying a test to encode it to mp4, 
but this command says:


./shm | ffmpeg -f image2 -r 30 -s 1274x541 -pix_fmt rgb32 -vcodec rawvideo -i - 
out.mp4

Could find no file with path 'pipe:' and index in the range 0-4
pipe:: No such file or directory

What am I doing wrong?

Thanks!

Josh


On Fri, 2 Sep 2016, Joshua Grauman wrote:

I've been looking for a way to screencast an app with alpha, but I haven't 
found one yet (but if someone knows of one, I'd love it). So I'm working on 
modifying my app to generate png's at 30 frames per second.


Josh


 2016-09-02 7:29 GMT+02:00 Joshua Grauman :
>  I have another different, but related question. What format would you
>  suggest for storing my screencast in? The resulting video is going to be
>  1080p30 and it needs to have an alpha channel

 Which screencast technology allows to record an alpha channel?
 mpng should be best for screencasts, some people like utvideo.

 Carl Eugen
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Re: [FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

I've been looking for a way to screencast an app with alpha, but I haven't 
found one yet (but if someone knows of one, I'd love it). So I'm working 
on modifying my app to generate png's at 30 frames per second.


Josh


2016-09-02 7:29 GMT+02:00 Joshua Grauman :

I have another different, but related question. What format would you
suggest for storing my screencast in? The resulting video is going to be
1080p30 and it needs to have an alpha channel


Which screencast technology allows to record an alpha channel?
mpng should be best for screencasts, some people like utvideo.

Carl Eugen
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Re: [FFmpeg-user] encoding video from png diffs

[Carles Vila]

>
>
>
> I have another different, but related question. What format would you
> suggest for storing my screencast in? The resulting video is going to be
> 1080p30 and it needs to have an alpha channel (the input png's will use the
> alpha channel). The screencast is going to be overlaid at a later time
> (with ffmpeg) onto another 1080p30 avchd video from my canon camera.
>

In order to overlay one video on top of another you don't need anything
related to an alpha channel.
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Re: [FFmpeg-user] encoding video from png diffs

[Carl Eugen Hoyos]

2016-09-02 7:29 GMT+02:00 Joshua Grauman :
> I have another different, but related question. What format would you
> suggest for storing my screencast in? The resulting video is going to be
> 1080p30 and it needs to have an alpha channel

Which screencast technology allows to record an alpha channel?
mpng should be best for screencasts, some people like utvideo.

Carl Eugen
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Re: [FFmpeg-user] encoding video from png diffs

[Carl Eugen Hoyos]

2016-09-02 10:21 GMT+02:00 Moritz Barsnick :

> $ ffmpeg -h encoder=ffvhuff

ffv1 should always work better than ffvhuff.

Carl Eugen
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Re: [FFmpeg-user] encoding video from png diffs

[Carl Eugen Hoyos]

2016-09-02 0:17 GMT+02:00 Cley Faye :

> $ your_script | ffmpeg -f png_pipe -i - out.mp4

It should not be necessary (would be a bug if so) to
specify the "_pipe" formats:
$ ffmpeg -i - out.mp4

Carl Eugen
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Re: [FFmpeg-user] encoding video from png diffs

[Moritz Barsnick]

On Thu, Sep 01, 2016 at 22:29:01 -0700, Joshua Grauman wrote:
> > from my program that I'm screencasting, which I haven't found screencast 
> > software that can do. Unfortunately, I'm not sure that I'm going to be able 
> > to get vcdiff to run fast enough to create the diffs at 30 frames/sec :(.
> I have another different, but related question. What format would you 
> suggest for storing my screencast in? The resulting video is going to be 
> 1080p30 and it needs to have an alpha channel (the input png's will use 
> the alpha channel). The screencast is going to be overlaid at a later time 
> (with ffmpeg) onto another 1080p30 avchd video from my canon camera.

All along, I was going to suggest: Why not use an existing codec? These
can have various advantages, such as they have already been analyzed
and optimized for performance, they can go into containers, they may
have safety measures such as I-frames (picture recovery mid-stream),
and so on. There are dozens of lossless codecs, and as many comparisons
out there. Some of them do support alpha, probably with ffmpeg as well.
You can check with:
$ ffmpeg -h encoder=ffvhuff
for the "Supported pixel formats:" output.

You will probably even find articles about saving screencasts
losslessly, and which codec to choose. But you can also experiment for
yourself.

> > Plus, this allows me to save the alpha channel from my program that
> > I'm screencasting, which I haven't found screencast software that
> > can do.

I don't understand your specific requirements, but ffmpeg can also
screencast:
https://trac.ffmpeg.org/wiki/Capture/Desktop
(If your alpha channel reflects the opacity of your windows, I presume
ffmpeg can't do that. But what do I know.)

Cheers,
Moritz
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Re: [FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

Hello everyone,

I have another different, but related question. What format would you 
suggest for storing my screencast in? The resulting video is going to be 
1080p30 and it needs to have an alpha channel (the input png's will use 
the alpha channel). The screencast is going to be overlaid at a later time 
(with ffmpeg) onto another 1080p30 avchd video from my canon camera.


Josh

The compression level is great. I thought of this because I am doing a 
screencast, so most screens are identical or very similar. So if I have an 
initial .tga file with size ~3 megabytes, most of the diffs will be less than 
1k in size (some will be more like 15k, and some quite a bit more, but those 
should just be single frames). Plus, this allows me to save the alpha channel 
from my program that I'm screencasting, which I haven't found screencast 
software that can do. Unfortunately, I'm not sure that I'm going to be able 
to get vcdiff to run fast enough to create the diffs at 30 frames/sec :(.


Josh


 On Thu, Sep 01, 2016 at 10:31:15 -0700, Joshua Grauman wrote:
>  So I know ffmpeg can encode video from a list of pngs. (img1.png, 
>  img2.png, img3.png, etc). But what if I have one png, and then a list of 
>  diffs (using vcdiff) like (img1.png, img2.diff, img3.diff, etc.).


 So you basically created a lossless codec of your own. ;-) How good is
 the compression level for your use cases?

>  I could of course generate all the pngs, but it would take up a lot
>  of space and I'm wondering if anyone knows of any creative way to do
>  this? Thanks!

 ffmpeg can handle image pipes. So what you would do is to pipe the
 first PNG to ffmpeg. Then create the seconds frame from img1.png and
 img2.diff, and pipe that to ffmpeg. Reuse that second frame to create
 the third one from img3.diff, and pipe that to ffmpeg. You can then
 always "reuse" or drop the previous result, and always have no more
 than two frames to keep for the moment.

 It would be something like
 $ create_png.sh | ffmpeg -f png_pipe -i - ...
 (Untested. create_png.sh could be a complex command line instead of a
 script.)

 I don't see any documentation right now, so just check
 $ ffmpeg -h demuxer=png_pipe
 I don't think you need most of the options, except the framerate
 perhaps.

 Disclaimer: I haven't actually tested this. ;-)

 Cheers,
 Moritz
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Re: [FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

The compression level is great. I thought of this because I am doing a 
screencast, so most screens are identical or very similar. So if I have an 
initial .tga file with size ~3 megabytes, most of the diffs will be less 
than 1k in size (some will be more like 15k, and some quite a bit more, 
but those should just be single frames). Plus, this allows me to save the 
alpha channel from my program that I'm screencasting, which I haven't 
found screencast software that can do. Unfortunately, I'm not sure that 
I'm going to be able to get vcdiff to run fast enough to create the diffs 
at 30 frames/sec :(.


Josh


On Thu, Sep 01, 2016 at 10:31:15 -0700, Joshua Grauman wrote:
So I know ffmpeg can encode video from a list of pngs. (img1.png, 
img2.png, img3.png, etc). But what if I have one png, and then a list of 
diffs (using vcdiff) like (img1.png, img2.diff, img3.diff, etc.).


So you basically created a lossless codec of your own. ;-) How good is
the compression level for your use cases?


I could of course generate all the pngs, but it would take up a lot
of space and I'm wondering if anyone knows of any creative way to do
this? Thanks!


ffmpeg can handle image pipes. So what you would do is to pipe the
first PNG to ffmpeg. Then create the seconds frame from img1.png and
img2.diff, and pipe that to ffmpeg. Reuse that second frame to create
the third one from img3.diff, and pipe that to ffmpeg. You can then
always "reuse" or drop the previous result, and always have no more
than two frames to keep for the moment.

It would be something like
$ create_png.sh | ffmpeg -f png_pipe -i - ...
(Untested. create_png.sh could be a complex command line instead of a
script.)

I don't see any documentation right now, so just check
$ ffmpeg -h demuxer=png_pipe
I don't think you need most of the options, except the framerate
perhaps.

Disclaimer: I haven't actually tested this. ;-)

Cheers,
Moritz
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Re: [FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

That's exactly what I need! Hadn't heard of the png_pipe option. I was 
thinking I might have to write a kernel module to create a bunch of /proc 
files or something! Thanks!


Josh

On Fri, 2 Sep 2016, Cley Faye wrote:


2016-09-01 19:31 GMT+02:00 Joshua Grauman :


I could of course generate all the pngs, but it would take up a lot of
space and I'm wondering if anyone knows of any creative way to do this?
Thanks!



​You could just do that. There is no need to write them anywhere though;
you can pipe png sequences into ffmpeg directly (I create animations this
way).

I'm not familiar with vcdiff, but as long as you have a tool that produce a
png on a standard output, you could loop over your diffs, piping the output
info ffmpeg. Maybe you'll need a temporary variable storing the resulting
png for the next step, but that will be held in RAM so no worries. Be
careful if you do that though; binary data and shell script variables are
not too friendly. I'd do that in python or another language.

Once you have your script that output the sequence of png on it's standard
output, you can pipe them to ffmpeg using '-' as the input name. Something
like this:
$ your_script | ffmpeg -f png_pipe -i - out.mp4
Don't forget to specify framerate etc.

(of course, if ffmpeg does support such format by itself, ignore this
message; I'm not familiar with *all* the stuff ffmpeg supports either).
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Re: [FFmpeg-user] encoding video from png diffs

[Moritz Barsnick]

On Thu, Sep 01, 2016 at 10:31:15 -0700, Joshua Grauman wrote:
> So I know ffmpeg can encode video from a list of pngs. (img1.png, 
> img2.png, img3.png, etc). But what if I have one png, and then a list of 
> diffs (using vcdiff) like (img1.png, img2.diff, img3.diff, etc.).

So you basically created a lossless codec of your own. ;-) How good is
the compression level for your use cases?

> I could of course generate all the pngs, but it would take up a lot
> of space and I'm wondering if anyone knows of any creative way to do
> this? Thanks!

ffmpeg can handle image pipes. So what you would do is to pipe the
first PNG to ffmpeg. Then create the seconds frame from img1.png and
img2.diff, and pipe that to ffmpeg. Reuse that second frame to create
the third one from img3.diff, and pipe that to ffmpeg. You can then
always "reuse" or drop the previous result, and always have no more
than two frames to keep for the moment.

It would be something like
$ create_png.sh | ffmpeg -f png_pipe -i - ...
(Untested. create_png.sh could be a complex command line instead of a
script.)

I don't see any documentation right now, so just check
$ ffmpeg -h demuxer=png_pipe
I don't think you need most of the options, except the framerate
perhaps.

Disclaimer: I haven't actually tested this. ;-)

Cheers,
Moritz
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Re: [FFmpeg-user] encoding video from png diffs

[Cley Faye]

2016-09-01 19:31 GMT+02:00 Joshua Grauman :

> I could of course generate all the pngs, but it would take up a lot of
> space and I'm wondering if anyone knows of any creative way to do this?
> Thanks!


​You could just do that. There is no need to write them anywhere though;
you can pipe png sequences into ffmpeg directly (I create animations this
way).

I'm not familiar with vcdiff, but as long as you have a tool that produce a
png on a standard output, you could loop over your diffs, piping the output
info ffmpeg. Maybe you'll need a temporary variable storing the resulting
png for the next step, but that will be held in RAM so no worries. Be
careful if you do that though; binary data and shell script variables are
not too friendly. I'd do that in python or another language.

Once you have your script that output the sequence of png on it's standard
output, you can pipe them to ffmpeg using '-' as the input name. Something
like this:
$ your_script | ffmpeg -f png_pipe -i - out.mp4
Don't forget to specify framerate etc.

(of course, if ffmpeg does support such format by itself, ignore this
message; I'm not familiar with *all* the stuff ffmpeg supports either).
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Re: [FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

Sorry, I just realized I forgot to mention I'm on Linux...

Josh


Hello all,

So I know ffmpeg can encode video from a list of pngs. (img1.png, img2.png, 
img3.png, etc). But what if I have one png, and then a list of diffs (using 
vcdiff) like (img1.png, img2.diff, img3.diff, etc.). Each diff would be based 
upon the last. I could of course generate all the pngs, but it would take up 
a lot of space and I'm wondering if anyone knows of any creative way to do 
this? Thanks!


Josh
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[FFmpeg-user] encoding video from png diffs

[Joshua Grauman]

Hello all,

So I know ffmpeg can encode video from a list of pngs. (img1.png, 
img2.png, img3.png, etc). But what if I have one png, and then a list of 
diffs (using vcdiff) like (img1.png, img2.diff, img3.diff, etc.). Each 
diff would be based upon the last. I could of course generate all the 
pngs, but it would take up a lot of space and I'm wondering if anyone 
knows of any creative way to do this? Thanks!


Josh
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