[MPlayer-users] Digitizing VHS tapes with mencoder

[Steve Fosdick]

On Tue, 6 Apr 2010 13:55:38 +0200
Josef Wolf <jw at raven.inka.de> wrote:

...
> So for the grab, I tried this command line:
> 
>  mencoder tv:// -tv
>  driver=v4l2:input=1:width=768:height=576:outfmt=yuy2:norm=pal:buffersize=100:forceaudio:alsa:adevice=hw.0,0,0:amode=1:immediatemode=0
> \ -oac copy -ovc copy -of avi -ofps 25 -o video.avi
> 
> But this complains really often about duplicated frames and dropped
> frames. I am somewhat concerned about those error messages. Will this
> have a big impact on recording quality?

The last time I tried something like this was back in 2000 but the
conclusion I came to at the time was that the PC could not write the
uncompressed video to disk fast enough to keep up with the live capture.

On the machine I had at the time it was also not possible to encode to
MPEG in real time.  The choices I could see were:

1. Some form of decimation, i.e. reduce the number of pixels in each
frame or reduce the colour depth.
2. Capture to MJPEG, i.e. where each frame is encoded as a JPEG image
but no inter-frame coding is done.

IIRC I went for the second one.

I reckon the factor by which CPUs have got faster these last ten years
is much greater than the factor by which disk I/O has got faster so it
may be worth trying to see if it is possible to encode direct to your
final format in real time.

> BTW: I've seen various resolution recommendations for PAL varying from
>      384x288 to 768x576. What is the correct setting?

In the output from a PAL VHS machine there should be 625 scan lines,
only 576 of which would normally be visible.  As the output is analogue
there isn't an number of pixels to be applied to the horizontal axis
but as the aspect ratio is 4:3 you could go for the same level of
detail in both directions and set the horizontal to 768.

For the original VHS the video bandwidth is only 3Mhz so the 768
horizontal resolution may be overkill - the Wikipedia article suggests
480 pixels may be sufficient.

Steve.