H.263 OMVIC Frequently Asked Question List

This page answers frequently asked questions about the H.263 omvic beta software.

1. Why does the application crash?

Well, there are several possible reasons. One thing that we have noticed is that streams sometimes have motion vectors specified in them. Currently, this causes the code to abort. To see if this is what is happening, check the debug output (note: Win32 users need to display the "Mash Console" by right-clicking on the omvic button in the Windows Taskbar to see the error messages).

2. Why does the image look bad at high quality (i.e., q<5)?

As described in the beta description, the H.263 bitstream does not have enough resolution to represent AC terms. Try turning on the Modified Quantization option using the command line flag "-codec h263:modQ" and see if that fixes the problem.

3. Why does video not show when I hit transmit?

This problem could be caused by several things. First, is the camera turned on and did you select the appropriate device? Second, did you specify the correct port and signal - remember the default is the first item in the list. Many capture boards and cameras are unable to automatically determine the appropriate signal (e.g., NTSC or PAL) so you have to select it manually. And, frequently, the device is connected to a different port (e.g., s-video, composite, etc.). Third, some Windows devices do not respond to the Video-for-Windows (V4W) code used in Open Mash. You can test your device by running the wmdev application in the distribution. It will open each device and attempt to configure it to produce various video formats. If you are having trouble, run this program and send us the results so we can try to fix our code.

4. Why do decoded blocks show as pink?

These blocks are coded as motion vectors. The current H.263 decoder does not handle motion vectors, so the blocks are displayed as pink. The omvic H.263 encoder does not produce streams with motion vectors, but streams produced by other H.263 codecs (e.g., uclvic, Polycom, Quicktime, etc.) do produce motion vectors so you are probably seeing a stream produced by another codec. Motion vector encoding and decoding will be added to a future release of the omvic H.263 codec.