Hi,
I was trying to use ffmpeg for screen capture and come to this problem.
I was using x264 for encoding with many different options, but the
result was unsatisfactory. Problem is with red colored labels, which are
really important in screen videos that should be captured. Here is
series of sample PNG pictures
http://tucniak.sk/ffmpeg/GrabedPictures.zip
It is just simple desktop with running Thunderbird with one email
selected as "Important" so it is red colored text in dark background.
Simple encoding via command line
ffmpeg -r 5 -i ./GrabedPictures/Pic%d.png -r 5 -vcodec libx264
TestX264.avi
made this result
http://tucniak.sk/ffmpeg/TestX264.avi
Everything is pretty sharp, except the red text in Thunderbird. Then I
used "lossless" option
ffmpeg -r 5 -i ./GrabedPictures/Pic%d.png -vcodec libx264 -x264opts
qp=0 TestLosslessX264.avi
Everything is almost the same, except the file size (almost twice), but
the red text still remains fuzzy
We have developed a simple grabber using ffmpeg library, where we used
hardcoded YUV444 colorspace and with that we made this video with
similar screen.
http://tucniak.sk/ffmpeg/OwnGrabX264_YUV444.avi
and the problem still remains.
I don't know how much "LOSSLESS" is the qp=0 option but it seems that
it is not enough to produce the same output as input. Can anybody give
some hint for options that could be used to make it REAL LOSSLESS.
For testing purpose I tried also "ffv1" and "huff" codec. I am not
posting the result videos because of the size, but you can do it
yourself by downloading GrabedPictures.zip and comands
ffmpeg -r 5 -i ./GrabedPictures/Pic%d.png -r 5 -vcodec huffyuv
OutHuff.avi
ffmpeg -r 5 -i ./GrabedPictures/Pic%d.png -r 5 -vcodec ffv1 -sameq
TestFfv1.avi
But these are not a good solution.
-Huff produced 270MB video from 50MB of PNG, and maybe I am doing
somethig wrong but direct playing PNGs as frames would be more
efficient.
-Ffv1 produced 22MB video which is some kind better but it is still too
much in comparison with 0,3MB for standard X264 and 0,6MB for "lossless"
X264.
What is more interesting when I was trying to play huff or ffv1 video
with mplayer or ffplay the red text was still fuzzy. So I thought that
even these codecs are not real lossless. Then by accident I played these
videos with vlc player and with this the red text was sharp. So the
problem was not encoding but decoding. It seems that ffmpeg has not
correct decoding of "lossless" video codecs.
Then I tried to play my "lossless" videos (TestLosslessX264.avi,
OwnGrabX264_YUV444.avi) with vlc hoping that the problem is just in
decoding. But again I was not successful. The first one shows only first
frame in vlc, and the second one only black screen.
Any hints or tips how to make "lossless" video with sharp red labels
are welcome
Best regards
Juraj Kolesar
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