[mythtv] [Experimental PATCH] BIG DVB PATCH V3.2 Released

Tue Dec 21 07:14:24 UTC 2004

On Tue, 21 Dec 2004 05:12 pm, you wrote:
> Mark Anderson wrote:
> > Big DVB 3.2
>
> It rocks.. doesn't it... :)

It's getting pretty good, once I get ac3 working then it might time start
thinking about getting the program guide integrated.

> >On my system it was not going into the do_ac3_passthru block becuase
> >autoSelectTrack was selecting non ac3 tracks for audio. I would also get
> >errors in the UI referring to incorrect number of audio channels when it
> >tries to configure the alsa device. This I believe was caused by the code
> >trying to configure the ALSA:spdif device with 5,7 or even 8 audio
> > channels, i.e it was not selecting the ac3 track. This is what my patch
> > for autoSelectAudioTrack solved for me. I am not sure if the patch was
> > the right thing to do but it certainly allowed do_ac3_passthru to become
> > enabled correclty, and for it to be disabled when no ac3 stream existed.
> > Not sure if the mpeg.c patch would have fixed this?
>
> Not sure, mpeg.c is just a hack that "preserves" the startcode at 0x1bd
> for a private stream, and set codec_id to CODEC_ID_AC3 when it sees a
> startcode of 0x1bd. (would be nicer if I can actually get the 0x80 part
> to work). Juha is also looking into this issue.. It could be a DVB only
> problem as Taylor says he got AC3 sounds from his HDTV (and so do many
> other pple)....

I applied the mpeg.c patch and it definitely imporved things, it now reliably
finds the AC3 stream when it is available, I get logs like this with AC3

2004-12-21 17:55:36.586 SIParser: AC3 Descriptor
2004-12-21 17:55:36.586 DVB#1 AutoPID selecting PID 514, Video
2004-12-21 17:55:36.587 DVB#1 AutoPID selecting PID 672, AC3
2004-12-21 17:55:36.587 DVB#1 AutoPID Complete - PAT/PMT Loaded for service
2004-12-21 17:55:36.587 DVB#1 Service is FTA
2004-12-21 17:55:36.588 DVB#1 Successfully tuned to channel 1592.
2004-12-21 17:55:36.590 DVB#1 Data read from DMX - This is for debugging with
transform.c
AC3 Audio:  BRate: 256 kb/s  Freq: 44100 Hz  Framesize 1024
Videostream: ASPECT: 16:9  Size = 1440x1088  FRate: 25 fps  BRate: 12.80
Mbit/s
2004-12-21 17:55:38.665 SIParser: SI Standard Detected: DVB

and like this with no AC3, note that there is no AC3 pid so it falls back to
pcm audio.

2004-12-21 17:56:05.436 DVB#1 AutoPID selecting PID 770, PCM
2004-12-21 17:56:05.436 DVB#1 AutoPID selecting PID 772, Teletext
2004-12-21 17:56:05.436 DVB#1 AutoPID selecting PID 769, Video
2004-12-21 17:56:05.436 DVB#1 AutoPID Complete - PAT/PMT Loaded for service
2004-12-21 17:56:05.436 DVB#1 Service is FTA
2004-12-21 17:56:05.437 DVB#1 Successfully tuned to channel 1330.
2004-12-21 17:56:05.439 DVB#1 Data read from DMX - This is for debugging with
transform.c
Audiostream: Layer: 2Videostream: ASPECT: 16:9  Size = 720x576  FRate: 25 fps
BRate: 15.00 Mbit/s
2004-12-21 17:56:07.133 SIParser: SI Standard Detected: DVB
2004-12-21 17:56:07.133 SIParser: SDT: sid=1328 type=1 name=7 Digital
2004-12-21 17:56:07.133 SIParser: SDT: sid=1332 type=1 name=7 HD Digital
2004-12-21 17:56:07.141 SIParser: SDT: sid=1329 type=1 name=7 Digital 1
2004-12-21 17:56:07.141 SIParser: SDT: sid=1330 type=1 name=7 Digital 2
2004-12-21 17:56:07.141 SIParser: SDT: sid=1331 type=1 name=7 Digital 3
2004-12-21 17:56:07.141 SIParser: SDT: sid=1334 type=1 name=7 Guide

However, there is still no audio when I select a channel sending AC3, I only
get audio when no AC3 is being sent. The front end is complaining about
"2004-12-21 18:00:20.230 No codec for stream index 2" so I will now have to
start tracning that code. I think it is getting much closer though.

> If you still have problems with ac3 passthru, check out what
> EncodeAC3Frame is actually doing.. Does it encode the data in another
> AC3 frame? What are the parameters that's passed in.. Is this the
> function that actually sends something to the external decoder?  I'm
> just speculating here.
>
> I assume you had already confirmed AC3 passthru to be working by using
> other softwares like mplayer, etc?

Works fine with dobly-city through mplayer

> >If I trace through the code in transform.c it doesn't seems to be reliably
> >finding the AC3 frame. I only occasionaly see the "AC3 Audio..." line in
> > the backend trace, and often it only apears when I stop watching TV,
> > which is a bit late! Occasionally a frame passes through all the tests
> > and gets written to the sound card which is when I hear brief noises come
> > from the decoder.
>
> Hmmm. different behaviour here.. When I switch to a HDTV channel,
> mythbackends always says it's AC3. if I switch to SDTV channel, backend
> says it's either Layer 1 or Layer 2, yadda yadda.
>
> What card, kernel and version of ALSA r u using? Me using Twinhan DVB-T
> and 2.6.9, with ALSA 1.0.7.

Dual Avermedia 771, alsa 1.0.7, FC3 with 2.6.5-1 kernel

> I can't watch HDTV properly, there are artefacts and jitters in it..
> Processor too slow (I am using Intel 2.6Ghz)? Or is it a bug (introduced
> by my mpeg.c hack perhaps?). my CPU usage is 30% when watching HDTV with
> bob, and 20% with xmvc and bob.

I'm not gonna bother until I get a display that can do HD, although I do get
similar symptons, maybe we need an option to disable the HD stations for poor
people like me without plasmas :-)

> Would have used xvmc and bob, but OSD flickers horribly... So I'm now
> back to SDTV. Do you know how do I switch the audio from mpeg to ac3 in
> SDTV?

The changes I made to autoSelectTrack will make it choose ac3 if it is
available, and PCM when it it not.

> Hope you can get ac3 working soon.. Share in this list what you did...

So do I, except once I get this going I have to get my dads box running with
software ac3 decode, but that's another story...

Mark

> Regards.

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