[mythtv] avcodec_dual_language flips on one channel (ticket #4976)

[Markus Schulz]

hello,

i have a problem with understanding the avcodec_dual_language switch. On 
one channel (ARD at Astra 19.2E) it flips regular and perhaps randomly?

for each pass from avformatdecoder.cpp:3372 mainloop (CODEC_TYPE_AUDIO 
switch) it looks like:
avcodec_dual_language =0
avcodec_dual_language =0
avcodec_dual_language =1
avcodec_dual_language =0
avcodec_dual_language =1
avcodec_dual_language =0
avcodec_dual_language =0
avcodec_dual_language =0
avcodec_dual_language =1
avcodec_dual_language =0
avcodec_dual_language =0
avcodec_dual_language =0
avcodec_dual_language =1
avcodec_dual_language =0
avcodec_dual_language =0

this results in splitting or not splitting to an additional stream and 
selecting a stream after them (for example the AC3 one) was impossible 
(without my hack, see ticket #4976).

Starting the stream gives the following AFD output:
-----------------------
2008-06-21 12:56:47.304 AFD: Opened codec 0x8ba8590, id(MPEG2VIDEO) 
type(Video)
2008-06-21 12:56:47.304 AFD: codec MP3 has 2 channels
2008-06-21 12:56:47.304 AFD: Opened codec 0x837f010, id(MP3) type(Audio)
NO SPLITTING
2008-06-21 12:56:47.304 AFD: codec MP3 has 2 channels
2008-06-21 12:56:47.304 AFD: Opened codec 0xa33fe00, id(MP3) type(Audio)
SPLITTING
2008-06-21 12:56:47.305 AFD: codec AC3 has 2 channels
No accelerated IMDCT transform found
2008-06-21 12:56:47.305 AFD: Opened codec 0xa2d32c0, id(AC3) type(Audio)
NO SPLITTING
-----------------------
SPLITTING means that AvFormatDecoder::ScanStreams splits the stream 
based on avcodec_dual_language.

Any ideas? A bug in ffmpeg or the stream from this channel was crap? 
What can we do in the latter case?

-- 
Markus Schulz