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Improve image quality of screencast

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Volker Bradley
Improve image quality of screencast
on Dec 11, 2010 at 4:24:55 pm

My screencasts are not as distinct as others that I see on youtube. Can you give me some suggestions?
Here are the three commands that I have tried to make screencasts:
1. ffmpeg -f alsa -ac 2 -ab 56k -i pulse -acodec pcm_s16le -f x11grab -r 30 -s 1680x1050 -i :0.0 -aspect 16:9 -vcodec libx264 -vpre lossless_ultrafast -threads 0 test.mkv
I uploaded this file directly to youtube. The result is:





2. ffmpeg -f alsa -ac 2 -ab 56k -i pulse -acodec pcm_s16le -f x11grab -y -r 60 -s 1680x1050 -aspect 16:9 -i :0.0 -async 0 -sameq screencapture.avi
I used DeVeDe to change the size to 1920x1080 and aspect ratio to 16:9
The result is




3. ffmpeg -f alsa -i pulse -f x11grab -r 30 -s 1680x1050 -i :0.0 -acodec pcm_s16le -vcodec huffyuv -sameq screencast.avi
Then compressed it to Divx/MPEG-4 with DeVeDe and converted the video to 1920x1080 and aspect ratio to 16:9
The result is





What is the proper ffmpeg command that I should use to make a crystal clear screencast?
Thanks.



My system is the following:
Serval Professional Laptop from System76
Operating System : Ubuntu 10.10 64 Bit
Processor : Core i7-920XM Processor Extreme Edition ( 45nm, 8MB L3 Cache, 2.0GHz )
Memory : 8 GB – DDR3 1066 MHZ 2 DIMMs
Hard Drive : 160 GB Intel X25-M Solid State Drive

Monitor attached with DVI:
Dell E207WFP 1680x1050 Refresh rate 59.88Hz
NVIDIA Driver Version 260.19.06

X Server Version Number 11.0
X Server Vendor Version 1.9.0 (10900000)
NV-CONTROL Version 1.24
Screens 1


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Michael Rampe
Re: Improve image quality of screencast
on Dec 21, 2010 at 1:07:05 am

[Volker Bradley] "My screencasts are not as distinct as others that I see on youtube. Can you give me some suggestions?"

It seems that all of you examples are being scaled in different ways, either by yourself, or by youtube.

To get the best results for screen capture material, keep the pixels intact without scaling.

Youtube HD is the same as 'normal' HD and comes in two sizes.
1920x1080 (1080p)
1280x720 (720p)

Seeing that your monitor has a max resolution of 1680x1050, I would aim for close to the 1280x720 size for CAPTURE and then CROP to 1280x720 for delivery. This will ensure that no scaling is done on the pixels and provide a crisp output.

For 1080p you might want to get a new monitor which supports a higher res. One of my monitors will do 1920x1200 which can have 120 pixels cropped from the top and/or bottom to provide a full HD unscaled output.

Michael


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Volker Bradley
Re: Improve image quality of screencast
on Dec 21, 2010 at 3:58:57 pm

Hi Michael,
Thank you for explaining this to me. I just did not understand the complexities of scaling.
Volker


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