Strange DGIndex behavior on 528x480 transport stream

[ekarbakar]

@neuron2
I took the liberty of uploading a 13mb .ts file to your ftp server '\pjones\050816224329'. Oddly, this file plays and sounds fine in VLC, but DGIndex won't produce an AC3 or WAV output. If I record 25 minutes or more of this same program, DGIndex locks up after setting the PID's (0x190, 0x191), requiring manual termination. I'm using the same capture program for a variety of other formats without problem. When you have some free time :-) ... would appreciate your insights.
PJ

[Guest]

I don't get any video or audio on the file you uploaded. HDTVtoMPEG2 also barfs on this stream that you uploaded. Are you saying that there is an application that can play *the stream you have uploaded*?

[ekarbakar]

Yes, VLC Media Player (www.videolan.org) plays video and audio perfectly. I tried HDTV2MPEG2 just now and it acts like it is converting, but produces a file with no video or audio. I checked the channel and the 5c bit is 0, so its not encrypted.

[Guest]

I suspected this day would eventually arrive. I just solved this same issue for one of STMicroelectronics' customers that was using one of our older video drivers. (Our more recent drivers handle it properly.)

At some point some clever person figured out that you can make a legal MPEG2 stream without any I frames at all (!), and thereby save bandwidth. The idea is to periodically send slices without forward referenced macroblocks in P pictures, instead of periodically sending I frames. When starting on a stream, over about two seconds the blocking artifacts (due to lack of I frame reference) clear from top to bottom of the picture as these special slices arrive. It almost looks like a wipe transition when a stream starts or the channel is changed. One service provider even used that as a branding concept, and shows the macroblocking on its promotional material!

So, your stream has no I frames, which causes severe problems for DGMPGDec. I was able to hack DGIndex to preview your stream (it's the History channel), but without I frames, I obviously couldn't generate a D2V file, because I could never start a "GOP line" (actually an I frame line), and if I could, it would be too long.

The problem is fixable and I will support no-I-frame streams in a future release. Thanks for raising this interesting case.

If you are thinking that this technique could be used to reduce the size of encodes without sacrificing any quality, you'd be correct. The MPEG2 encoder needs to support it. Calling Hank. :)