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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I have tried to decode a LPCM DVD like compliant audio
stream with VLC Media player inside an Mpeg2 program stream. And VLC Media
Player nicely recognized the audio stream and played it as well as the accompanied
Mpeg2 Video stream in the Mpeg2 program stream. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I used LiveMedia testMPEG1or2ProgramToTransportStream.cpp
testing application to create a transport stream wrapping the Mpeg2 DVD like program
stream. Using an Mpeg2 Stream Analyser from Elecard I was able to find that
LiveMedia created the properly Mpeg2 Transport stream around the program
stream.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I have tried to playback the created Mpeg2 Transport Stream
with VLC and though the video played nicely the audio wasn’t decoded. I
Opened the Message Dialog Box of VLC and found that the LPCM Audio Codec wasn’t
instantied this time.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I downloaded VLC source code and began investigating the problem.
I checked through the file “ts.c” trying to find what going on. I quickly
found the code where the private type 0x06 of the packetized elementary stream is
checked to find what data is carried. My understanding of the code is that LPCM
audio is detected inside a private stream when the Mpeg-2 descriptor is matched
with “BSSD” (Line 2961 of ts.c).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Now looking at the Website:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><a href="http://www.smpte-ra.org/mpegreg/mpegreg.html">http://www.smpte-ra.org/mpegreg/mpegreg.html</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><a href="http://www.smpte-ra.org/mpegreg/bssd.html">http://www.smpte-ra.org/mpegreg/bssd.html</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I found that BSSD is associated to the mapping of audio data
as specified in SMPTE Standard SMPTE 302M-1998 for Television which is “Mapping
of AES3 Data into MPEG-2 Transport Stream”. This is a LPCM audio
stream formatted according to AES3.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I have found that LiveMedia doesn’t add the descriptor
when wrapping the transport stream. Then for sure the audio will never be
recognized.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Now will adding the BSSD descriptor solve the problem? Well
I did not try it but I expect it will properly decode the audio stream. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>However when doing that I will create an improperly association
between the audio data and the BSSD descriptor and thus have an illegal Mpeg2
Transport Stream that won’t be recognized by other decoder. Why ? Because
the BSSD description create an association with an audio AES3 formatted LPCM P-ES
stream. Not a DVD-Video audio LPCM formatted P-ES. They do not share the same
formatting. The LPCM audio codec “lpcm.c” used by VLC is clearly a
formatted DVD-Video audio LPCM codec. Not an AES3 LPCM formatted audio codec.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I suspect that the descriptor to be used to create the
properly association is: “DVDF”. Please check:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><a href="http://www.smpte-ra.org/mpegreg/dvdf.html">http://www.smpte-ra.org/mpegreg/dvdf.html</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Unfortunately I do not have any stream sample of a DVDF
Mpeg-2 transports stream to double check my finding. But I believe this is an
issue that will prevent the decoding of a complient DVDF Mpeg-2 transport
stream.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Anyone having a DVDF compliant stream could confirm my
finding please ?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Guy Bonneau<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
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