Sound over HDMI does't work

I have Intensity Pro PCIe card and can capture video and audio from settopbox if it is playing DVB-T broadcast. But I got no audio when it is playing some file from USB flash.

I suspect that settopbox is sending compresed audio over HDMI and Intensity pro card does't support it. Can someone confirm it?

Most likely yes, your box may be outputting AC3 a consumer format for encoding surround sound. Consumer TVs and hifis will be able to decode this kind of signal but it is by no means a professional standard. You may want to try another file and see if can work, one you know has PCM encoded audio. There may be a setting somewhere for playback also.

The intensity card will not capture AC3 audio.

Thank you. I tried playing file with PCM audio but it didn't worked either. So there is no way to get it work with AC3? Like install some additional codecs. My current workaround is set input to HDMI+analog audio through SCART.

AC3 is a convenient consumer format, unlikely to be supported in any professional product. I am not sure why PCM does not work. A settob box is far from a professional product and may or may not adhere to standards for pro video hardware. If you have it working through the analogue connections then maybe that will be the best solution.