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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