[mythtv] DVB Changes / Patch Applied
markjanderson at mail.com
Tue Jan 25 05:41:17 EST 2005
> -----Original Message-----
> From: mythtv-dev-bounces at mythtv.org
[mailto:mythtv-dev-bounces at mythtv.org]
> On Behalf Of Tim Davies
> Sent: Tuesday, January 25, 2005 12:39 AM
> To: Development of mythtv
> Subject: Re: [mythtv] DVB Changes / Patch Applied
> As far as I can see, this patch (oz-ac3.diff) does at least four
> > 1) wantac3 setting in the setup
> > 2) make the PS autopid use <1>
> > 3) make AvFormatDecoder::autoSelectAudioTrack use <1>
> > 4) deal with codec changes (?)
> > <1> & <2> looks conceptually good to me although I'd implement it
> > slightly differently, partly because I'm planning on removing the
> > preferredFooStream hack completely and move that logic into
> > dvbrecorder. I'd also call it "ac3wanted" or something to make it
> > together with "ac3passthrough". I also have an idea for the
> > dvbrecorder which, if it works, will make it possible to record
> > multiple audio streams with PS recording too and then we won't need
> > <2> any more. I think this would also eliminate parts of the
> > patch. Once Taylor gets things going with the followup patch I'll
> > and sort this part out...
> > I haven't looked that much at the rest of the patches (ffmpeg and
> > avformatdecoder is pretty much new territory to me) but you've seen
> > what Isaac said. I think it would help if you could identify more
> > clearly exactly what the problems are and how to fix them. And trim
> > down and split it up in distinct parts. Maybe some more comments?
> > like to help but I don't understand the patch yet and my time is a
> > limited. :(
> I guess 1,2,3 are all to do with getting the preferred track into the
> recording and then chosen for playback. It is quite common here to
> both an MPEG2 and AC3 audio track in a service. The ideal solution
> me) is for both the PS and TS to record both audio tracks, and then
> is auto selected on playback but can be overridden by the user. I'm
> some would disagree though :-p.
> Part 4 is the important bit. It reinits the audio if it detects a
> change, as well as (what it did previously) detect the change in
> rate and/or the number of channels.
> There were a couple of extra bits as well, like not aborting when a
> decoder wasn't found. I'm not sure whether Mark did this just while
> testing, but I know from experience that the frontend would crash if
> did abort. If you have multiple tracks, you'd really want to see if
> can decode the another one before giving up entirely.
> Does anyone else out there have multiple audio tracks? I would have
> thought this kind of thing would be a necessity...
> I'm also a bit reluctant to do too much; this is Mark's baby - I'm
> pushing it along...
I'm glad to see the DVB patch into CVS, great work to all involved and
thank you. I will take Tim's version of the patches to CVS and apply
them tomorrow, get everything up and running and then start thinking
about how to get the AC3 into CVS. Since it is a lot of different fixes,
maybe lot of different patches is the way to go. A number of the changes
are discrete fixes in their own right and so can be applied
independently of the whole. From memory they include:
1. Fix for a crash in avformatdecoder when an unknown audio codec is
2. Auto selection of AC3 tracks when they are available, including the
option to disable AC3 all together (in case you have no AC3 decoder).
3. Fix for transform.c to correctly transform the AC3 audio (include the
full private stream header and fix problem with AC3 header detection).
4. Hack for mpeg.c to re-use the one audio track. This needs the PS
multi track recording enhancement.
5. Change to mpeg.c to notify avaformatdecoder of a change to the audio
tracks via a callback function (the call back was already there just
wasn't getting called in the right spot)
6. Enhance avformatdecoder to re-initalise the audio when a change in
codec is encountered.
??Did I miss anything??
With all of the above applied AC3 audio will work, at least here in OZ
and probably in Europe.
The biggest problem at the moment is sorting out the mpeg.c hack to only
record a single audio track. Having the PS recording record all audio
tracks is the right answer here, I am happy to code it if someone can
point me in the right direction.
BTW I noticed channel 7 are going to play the IMAX movies in HD and
Surround Sound over the coming weeks, should be an interesting test for
myth DVB and AC3 (if they use it?)
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