dvb-t ac3 recording

[daza67]

In Australia some of our dvb-t channels utilise ac3 audio even for standard definition channels. Live viewing of ac3 channels works okay using the microsoft dvr-ms muxer however recording or timeshifting results in no audio.

I have tried the other mux options such as intervideo (3.0.79.81) and cyberlink (5.0.0.1307) these both result in no audio for live tv. The cyberlink mux records an mpg file without audio. The intervideo mux refuses to record anything.

I figure the dvr-ms muxer is probably the best bet as it appears capable producing of ac3 dvr-ms files with webscheduler. I have read on other forums that the cyberlink muxer is not ac3 capable, i'm unsure about the intervideo muxer.

Any ideas ? I can supply a full .ts file for testing if required.

Daza

[daza67]

Here are some more files that may help with debuging.

[fooman1]

Hi mate,

I also have the same problem, except I can't seem to get audio to work on AC3 channels even in Live TV. I've tried AC3filter, Nvidia's Audio decoder, Nero Digital, and another one or two to no avail.

[daza67]

Hi mate,

I also have the same problem, except I can't seem to get audio to work on AC3 channels even in Live TV. I've tried AC3filter, Nvidia's Audio decoder, Nero Digital, and another one or two to no avail.

I can get AC3 audio working on live tv using the nvidia audio decoder set for spdif out. This only works for me when using the microsoft dvr-ms muxer. As mentioned above recording or timeshifting results in no audio at all.

Make sure you have live preview enabled so you are not timeshifting by default. Make sure spdif out and ac3 passthough is also enabled on your soundcard. Does ac3 work on dvd playback with the same audio and video decoders selected ?

[fooman1]

Take a look at DVB Webscheduler for recording the HD channels - http://wiki.dvbowners.com/index.php/WebScheduler - Not the best if you want an all-in-one solution but at least it'll work in the meantime.

I've got my HTPC outputting through the analogue jacks to my stereo which has the 5.1 speakers connected to it, so unfortunately AC3 passthrough is useless to me. DVD playback is fine, as are the HD channels on any of the other HTPC programs (MCE2005, MediaPortal, DNTV Live!) using the same decoders.

[fooman1]

To be honest I have a sneaking suspicion that it may be the MPEG-2 demux that is causing the problem. Taking a look at the lastgraph.grf file in GraphEdit and even modifying the config.xml file to let me use other audio codecs, it seems that everything is connected fine but with no change in the playback of AC3 audio. These codecs all work fine in other applications.

Is there a way to force GB-PVR to use a custom grf file? That way, it would be possible to test different MPEG-2 demuxes. Alternatively, is there a way to force GB-PVR to use a different demux?

[daza67]

This is interesting, if I turn live preview mode off and start viewing on a mpeg audio tv channel then change to an ac3 tv channel it works.

I agree it's something to do with the mpeg-2 demultiplexer configuration or the ac3 audio connection to the stream buffer sink.

Daza

[fooman1]

You're certainly onto something, as I just tried that and the audio worked for me. I'm not 100% it's 5.1 as I didn't test for long and I don't think the source was 5.1. However, the main thing is that something worked. Unfortunately, I discovered that when in timeshift mode, the nVidia PureVideo video decoder is not used, rather the Mpeg2Dec filter is.

I did a few tests with other software and GraphEdit for comparison's sake. Using MCE 2005 (where TV is always buffered) the graph was similar to that used by GB-PVR in timeshift mode, except the MCE graph included a "Decoder/Tagger Filter" stage on each of the DVR Outs from the video file prior to going to the video/audio decoders, something which GB-PVR does not use. Also, MCE correctly uses the decoders I have set, whereas GB-PVR, as mentioned above, seems not to let me change from Mpeg2Dec for video decoding in timeshift mode.

For live TV viewing, I compared with MediaPortal which works fine on the HDTV channels. There were three main differences on the MediaPortal live TV graph. First, the MPEG2 Transport output from the BDA device goes to the input of a "Sample Grabber" rather than straight to the MPEG-2 Demultiplexer. The output of this "Sample Grabber" block goes to the MPEG-2 Stream input of the MPEG-2 Demultiplexer.

Second, the MPEG-2 Demultiplexer is different to the one used by GB-PVR. The GP-PVR MPEG-2 Demultiplexer block includes five output pins: 1, 5, PSI, audio and video. The MPEG-2 Demultiplexer used by MediaPortal has many more output pins: 1 (to IB Input of BDA MPEG2 Transport Information Filter), 2 (to Input of Stream-Analyzer), 3, 4, 5, AC3 (to In on MPEG/AC3/DTS/LPCM Audio Decoder), audio, audioMpg1, EPG (to EPG on Stream-Analyzer), MHW1 (to InputD2 on Stream-Analyzer), MHW2 (to InputD3 on Stream-Analyzer) and video (to Video Input on NVIDIA Video Decoder).

The last major difference is the inclusion of a Stream-Analyzer block, which takes inputs mentioned previously from the MPEG-2 Demux but has no outputs.

This is why I think the Live TV viewing problem lies with the MPEG-2 Demux. If it were possible to force GB-PVR to use a specific graph file, we would be able to test this properly.

[fooman1]

Hi daza67,

It appears there is a solution for getting audio on HDTV channels, at least while watching in live TV. Open your config.xml file in your GB-PVR directory and find the BDAQuickPidSwitch entry. It will be set to true. Change it to false, save the file, reload GB-PVR and try your HDTV channel. Not sure if this will be AC3 5.1 audio or whether it is only 2 channel.

However, now if I go to record manually (or timeshift), if I am on a HDTV channel, there will be no sound. I need to turn it to a normal channel without AC3 first and then change it back so that I can get sound on the HDTV channels and recordings. This is basically the same as before, I guess. I assume that an automatic recording will not have sound.

I'm not sure what the BDAQuickPidSwitch is for and whether it is important to be on true. Also, I now notice stuttering on the HD channels in Live TV mode. CPU usage is less than 50% (dual core processor). Not sure yet whether this is simply related to the video codec. Changing from PureVideo to the Cyberlink DTV decoder seems to have fixed the stuttering issue for some reason.

[sub]

If it were possible to force GB-PVR to use a specific graph file, we would be able to test this properly.

No, there is no way to get GB-PVR to use a custom .grf file. This would require a huge amount of work, and not worth it in my book. Its not as simple as it sounds.

For live TV viewing, I compared with MediaPortal which works fine on the HDTV channels. There were three main differences on the MediaPortal live TV graph. First, the MPEG2 Transport output from the BDA device goes to the input of a "Sample Grabber" rather than straight to the MPEG-2 Demultiplexer. The output of this "Sample Grabber" block goes to the MPEG-2 Stream input of the MPEG-2 Demultiplexer.

Second, the MPEG-2 Demultiplexer is different to the one used by GB-PVR. The GP-PVR MPEG-2 Demultiplexer block includes five output pins: 1, 5, PSI, audio and video. The MPEG-2 Demultiplexer used by MediaPortal has many more output pins: 1 (to IB Input of BDA MPEG2 Transport Information Filter), 2 (to Input of Stream-Analyzer), 3, 4, 5, AC3 (to In on MPEG/AC3/DTS/LPCM Audio Decoder), audio, audioMpg1, EPG (to EPG on Stream-Analyzer), MHW1 (to InputD2 on Stream-Analyzer), MHW2 (to InputD3 on Stream-Analyzer) and video (to Video Input on NVIDIA Video Decoder).

The last major difference is the inclusion of a Stream-Analyzer block, which takes inputs mentioned previously from the MPEG-2 Demux but has no outputs.

These differences dont matter. GB-PVR already uses the right filters, hooks things up the right way, and creates all the correct demux pin names.

The only part that is likely related to the lack of AC3 is when GB-PVR creates the 'audio' pin on the demux filter it tells it the specific media type to use for the pin, it may be doing this wrong. You can right click on the 'audio' pin to view the pin properties, which will show the media type.

A tuning request normally looks like this in your logs:

BDARecorder:::StartRecording(Twinhan DVB-S (DVB-TV 878 Digital Tuner Driver), 1, , T:12456,V,22500,56~P:1035~V:512~A:650~L:eng~PMT:257~TXT:578~N:>TV One)

Where it says "L:eng" it can also have an optional "(AC3)" appended. This is used to tell GB-PVR that it should create an AC3 pin rather than a MPEG1 Layer 2 pin.

I dont have access to any AC3 broadcasts myself, so this has never been tested.

I have made one change for the next release that may help AC3 recordings using the Cyberlink Mux.