50fps to 25fps

[minchjp]

How do I convert a captured HDTV (720x576) file with a framerate of 50fps to 25fps, without re-encoding? I have a m2v file and an audio file.

[bugster]

Provide some more details on the source file. A Gspot screenshot would probably help.

BTW, How do you capture HDTV at 50fps?

[minchjp]

The file is a 576p HDTV rip, which i recorded of my DVB-T card. The dimentions are 720x576, it is a PAL mpg2.

Note: This is not an analogue capture.

GSpot doesn't work with mpg2 files.

Thankyou for the help.

[bugster]

If it really is 50 frames per second progressive, then the only thing I can think of would be to use avisynth to select every 2nd frame, then use this to framserve to an encoder. I doubt you could find a way without re-encoding, but I could be wrong!

[bugster]

.

GSpot doesn't work with mpg2 files.

The latest version does according this

[bosss7]

If it's 576p then the footage already IS 25fps. 50fps footage is usually reffered to as interlaced. 25 frames of odd fields and 25 frames of even fields = 50fps.

50fps would be completely useless as the human eye can only see something like 24-30fps. Hence motion picture stuff is filmed at 24fps. 50fps progressive would be a waste of signal.

[gastorgrab]

If it really is 50 frames per second progressive, then the only thing I can think of would be to use avisynth to select every 2nd frame, then use this to framserve to an encoder. I doubt you could find a way without re-encoding, but I could be wrong!

Something like this i'm guessing;

SelectEvery (4, 1, 2)# Assuming TFF
Weave ()

Would there be a problem with Up and Down shifting?

[minchjp]

I have a screanshot from DVD2AVI, does anyone know why it says NTSC??

[bugster]

If it really is 50 frames per second progressive, then the only thing I can think of would be to use avisynth to select every 2nd frame, then use this to framserve to an encoder. I doubt you could find a way without re-encoding, but I could be wrong!

Something like this i'm guessing;

SelectEvery (4, 1, 2)# Assuming TFF
Weave ()

Would there be a problem with Up and Down shifting?

I am no avisynth expert, but I don't think that would do waht I was think of. I don't see the need for weave() if the source is really 50fps progressive as the OP seems to think it is.

Simply SelectEven() or SelectOdd() would be sufficient. You might want to use AssumeFrameBased() at the start of the script just to be safe.

I have to agree tho, 50fps progressive does seem unlikley

[minchjp]

PVAStrumento said the following about the captured file:

***
*** PVAStrumento 2.1.0.13
*** running at 02-06-2005 22:24
***
Pre-Scanning input. Takes some time.
Stream info for
D:\Digital TV Recordings\7 HD Digital(05-02-05 21-30-07).mpg

Found 1 video stream.
Found 1 MPEG audio stream.

VIDEO #1
Resolution 720 x 576 (full D1)
Aspect ratio is 16:9
Frame rate 50.00 fps
Nominal bitrate 9000000 bps
First PTS: 00:00:00.020

MPEG AUDIO #1
MPEG1, Layer 2
stereo, sampled at 48.0 kHz.
Bitrate 256 kbps
Each frame contains 24.0 ms audio (768 bytes)
First PTS: 00:00:17.211

[bugster]

Thats some strange properties. What is the card you used to capture it with, what was the source transmission. Which country/satellite channel/broadcast Tv station.

Can you open it in virtualdub_mod and see what that says for file properties.

[lordsmurf]

That file looks whacked. I bet the header is corrupt.

[gastorgrab]

I am no avisynth expert, but I don't think that would do waht I was think of. I don't see the need for weave() if the source is really 50fps progressive as the OP seems to think it is.

Yeah, i don't get much experience with PAL stuff here in NTSC land.

[minchjp]

Thats some strange properties. What is the card you used to capture it with, what was the source transmission. Which country/satellite channel/broadcast Tv station.

Can you open it in virtualdub_mod and see what that says for file properties.

OK.
Card: VisionPlus HDTV - TwinHanDTV software to record.
Scource Transmition: Channel 7 Perth HDTV (576p) - 720x576
Country: Australia (All FTA Digital TV in australia is DVB-T)

If it helps the show is Desperate Housewifes

Here are the VirtualDub information:


If the frame rate is 25fps, and the header tells the software that it is 50fps, then theoreticly, the play time should be halved, but it is not. All information suggests it is 50fps.

BTW, thanks for the help everyone

[bugster]

If the frame rate is 25fps, and the header tells the software that it is 50fps, then theoreticly, the play time should be halved, but it is not. All information suggests it is 50fps.

You would have thought so wouldn't you!

If it truly is 50frames per second, then as I suggested above, avisynth can select every second frame and the frameserve to an encoder. A little easier is virtuadub mod which IIRC has a built in 'decimate' filter which I think does the same kind of thing (not sure about that tho).

[zilog_jones]

Desparate Housewives is filmed, which means it's 25fps in PAL. If you look at the video frame-by-frame you should find that every two frames are indentical.

And bosss7, you don't know what you're talking about. Nealry all footage taken from video cameras is 50/60 fields-per-second interlaced or 50/60p