NTSC and PAL AVI format error ?

[TimHaymes]

Hi Robin,
There is a an apparent problem with the SC 4.1 AVI 25fps recording. The settings and recorded frame rate indicate 25 FPS, but this is not set correctly in the AVI header (?). When the file is read by Tangra (for occultation analysis) I get a warning it is 30 FPS (NTSC). This causes a problem later on in the analyse flow. BUT the time between frames in the AVI is 0.04sec and agrees with the on-frame GPS time.

I have spoken to another observer (on a different forum) who gets the same problem. He found a work-arround using Virtual Dub

Can this problem be solved in SC, if indeed the problem is there ?

Many thanks.

Tim
(Abingdon)
WAT910HX + Pinnacle Dazzle HD grabber to W10 via USB3. SC 4.1.13218

[admin]

Hi Tim,

right now, SharpCap always puts 30fps into the AVI header. There are a couple of reasons behind using this value

1) In general, the 'frame rate' is not a well defined thing in SharpCap. Webcams have a frame rate, but most other cameras don't - you set the exposure and maybe USB speed/resolution settings and then you *get* some frame rate come out, but you aren't directly in control of it.

2) Often, SharpCap is used for longer exposure imaging, so a 'real' frame rate would lead to an AVI that played back very slowly (1fps or less?). Setting 30 gives a reasonable playback speed.

I guess my first suggestion here would be to use SER files instead of AVI (or even ADV files). Both of those have per frame timestamps stored in the file that are accurate as far as they can be (ie SharpCap records the time it gets the image data - obviously the actual capture was at some point before that time). My usual feeling is that AVI is really only suitable as a casual capture format for (mostly) non-astro imaging.

cheers,

Robin

[procyon12]

Hi Tim, all,

Please never use SC with AVI for occultation work (unless you have an analogue 30 fps camera or grabber). We sometimes see such reports on SODIS. It is always a lot of effort to get results from them, if it is at all possible.

Cheers

Christian

[TimHaymes]

Hi Christian / All,
Thanks for your comment, I accept your advice.

For PAL WAT910HX, I have been informed by Jan Manek (CZ) that video file header (30 FPS) can be changed in Virtual Dub2 and re-saved as 25 FPS without affecting the actual frame rate which is correct. I have tested this and found it works as a fix.

Cheers, Tim

[procyon12]

Yes, I know this fix too ... However, it is better not to use AVI.

Christian