[mythtv] [mythtv-commits] Ticket #2556: Bogus video streams in output PMT

[Neil Murphy]

David Matthews wrote:
> Stuart Auchterlonie wrote:
>> On Tue, Oct 10, 2006 at 02:39:08PM +1000, Andrew Dennison wrote:
>>
>>> On 10/10/06, Daniel Kristjansson <danielk at cuymedia.net> wrote:
>>>
>>>> On Mon, 2006-10-09 at 14:21 +0000, MythTV wrote:
>>>>
>>>>> #2556: Bogus video streams in output PMT
>>>>> The invalid streams (0x4ae & 0x40d) are only found
>>>>> in the output PMT, not in the recording itself.
>>>> Perhaps something in the DVBRadio & MHEG dummy video support?
>> Digging into this a bit more, from [10458] we added
>>
>> {{{
>> if ((dvbci.component_tag >= 0) && (stream_type == STREAM_TYPE_PRIVATE_DATA))
>> {
>>     /* Audio and video are sometimes encoded in private streams labelled with a component tag. */
>>     if (dvbci.language[0])
>>         stream_type = STREAM_TYPE_AUDIO_MPEG2;
>>     else
>>         stream_type = STREAM_TYPE_VIDEO_MPEG2;
>> }
>> }}}
>>
>> This will effectivly classify any data stream as a Video stream
>> if it is in a private data stream and is not an audio stream.
>>
>> >From research I did when looking into DSMCC, I found that in the
>> private streams there were consistent component tags to tell me
>> what they really were. I can't remember the specific values at
>> the moment but will look it up when I get home. The above check
>> really should be written as.
>>
>> {{{
>> if ((dvbci.component_tag == AUDIO_TAG) && (stream_type == STREAM_TYPE_PRIVATE_DATA))
>>     stream_type = STREAM_TYPE_AUDIO_MPEG2;
>>
>> if ((dvbci.component_tag == VIDEO_TAG) && (stream_type == STREAM_TYPE_PRIVATE_DATA))
>>     stream_type = STREAM_TYPE_VIDEO_MPEG2;
>> }}}
>>
>> as per other checks. I'll look into this when I get home.
>>
> 
> It's certainly possible that this is what's causing the problem but the
> above won't work.  The reason for this code is to enable an MHEG
> application to select a different audio or video stream from that given
> in the PMT.  For example, sometimes there are different commentaries
> available on a sports match.  In a few cases, I think BBC Parliament is
> an example, there is no stream labelled as "video" in the PMT so without
> this there would be no video.
> 
> The MHEG application selects a stream by its component tag and calls
> SetAudioByComponentTag or SetVideoByComponentTag to do this.  The reason
> for using component tags is that PIDs could change as a result of
> remultiplexing so it isn't a good idea to have a PID in an MHEG app.  As
> far as I know there is no standard numbering for the tags.  They are
> just arbitrary values.  The streams, though, are marked as private data
> in the PMT.  The complicated part is to present the information to
> avformatdecoder so that SetAudioByComponentTag and
> SetVideoByComponentTag will work.  The only way I could see to do this
> was to try to predict which could be audio and which video within
> mpegts.c and then include them in the available streams.  It would
> certainly be better to drive this from the other end and only treat a
> stream as, say, audio, once SetAudioByComponentTag was called.  I just
> couldn't see how to do that.
> 
> If this is the source of the problem it could be that the problem is the
> selection of the default video and audio streams is wrong.
> 

It certainly seems to be. I've just tried the following hack and I now
have channel-4 working again!

fnm at saruman:/usr/src/mythtv_svn/mythtv> svn diff
Index: libs/libmythtv/avformatdecoder.cpp
===================================================================
--- libs/libmythtv/avformatdecoder.cpp  (revision 11515)
+++ libs/libmythtv/avformatdecoder.cpp  (working copy)
@@ -1351,9 +1351,9 @@
                 enc->decode_cc_dvd  = decode_cc_dvd;

                 // Set the default stream to the stream
-                // with the lowest component tag.
+                // with the highest component tag.
                 if (selectedVideoIndex < 0 ||
-                    ic->streams[i]->component_tag <
+                    ic->streams[i]->component_tag >
                     ic->streams[selectedVideoIndex]->component_tag)
                 {
                     selectedVideoIndex = i;

Neil.

> >

> David.
> 
> _______________________________________________
> mythtv-dev mailing list
> mythtv-dev at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-dev