Autor Thema: Options for external (S-Video) input capture  (Gelesen 8036 mal)

sssmmmddd

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Options for external (S-Video) input capture
« am: Dezember 01, 2010, 05:30:37 Nachmittag »
Hi all,

I have tried to use the Sundtek MediaTV Pro to do a desktop capture, where I used a König CMP - TELVIEW2 (PC-TV) VGA to TV (composite, S-Video etc) converter.

Basically, I set the desktop to 800x600, and have it cloned on VGA; then I plug the VGA into the König; finally I use S-Video cable as output from the König, and into the Sundtek (via that small cable plug that looks like mini USB, that has S-Video input connector).

Then I open VLC; go to Media/Open Capture Device; enter /dev/video0 for the 'Video device name', and click 'Play'; first I get analog TV static/noise.

Then I do:
$ mediaclient -i
Using device: /dev/video0
ID     | Input
--------------
0000   | Television
0001   | Composite
0002   | S-Video

$ mediaclient -I 0002
Using device: /dev/video0
Setting input: 0002 ... (S-Video) ... done

and then I can see the captured VGA desktop in VLC.

Now, the resolution that is recognized by VLC from the Sundtek stream is 720x576. The original 800x600 looks scaled down to fit in these 720x576, along with a black frame/border. One can 'zoom' from the König device, and thereby use up some of that black frame/border, but I would guess, originally the 800x600 is made into 680x480, and then centered in 720x576.

However, I originally hoped, that this kind of a system would give me 800x600 video - with a quality of an uncompressed desktop screenshot, plus whatever compression the Sundtek has to perform on the signal; and this was important to me, because I don't like fonts heavilly blurred, or with compression artefacts.

As it the scaling down causes fonts to blur - my first question is: is there any way to, possibly, set the capturing resolution of the Sundtek to something else than 720x576 - or is this a limitation of S-Video signal? (in that case, I would hope to set capture resolution to 800x600 in Sundtek, and use the König to 'stretch' the video back again to the original 800x600).

My second question is - what would be the recommended way, for me to capture this S-video stream from Sundtek, directly from the command line (without using VLC)? And hopefully uncompressed (i.e. without additional video compression, than the one coming from the hardware itself)..

Thanks for any suggestions in advance! 

Sundtek

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Re:Options for external (S-Video) input capture
« Antwort #1 am: Dezember 01, 2010, 05:42:31 Nachmittag »
The hardware does not support any compression.

720x576 is PAL-BG quality, the black frame must be created by your converter device.

As I see your converter device only supports:
640x480
800x600
1024x768
etc.

The problem is that this device does not seem to support true 720x576


We highly recommend that you compress the video, since raw video requires 20 mbyte/sec

for example you can use mencoder:
Zitat
mencoder -tv norm=PAL-BG:adevice=/dev/dsp0:amode=1:audiorate=48000:input=1 (0 tv, 1 composite, 2 svideo) -af format=s16le -ovc lavc -lavcopts vcodec=mjpeg -oac pcm -o test.avi tv://

Another customer reported that he had to add a framerate parameter :fps=25

the cpu usage with a 1.3 ghz notebook was 15% on one core for encoding.

hope this helps
Failure is a good thing! I'll fix it

sssmmmddd

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Re:Options for external (S-Video) input capture
« Antwort #2 am: Dezember 01, 2010, 05:56:42 Nachmittag »
Hi Support,

Zitat
hope this helps

It does, a lot - had no idea 720x576 is standard PAL-BG quality :)

Thanks a lot for the prompt answer!

PS: Thanks for the cmdline suggestion too!