[mythtv-users] Why does channel 4 transmit a silent audio track as well as the normal audio?

Nick knowledgejunkie at gmail.com
Wed Aug 31 02:01:18 UTC 2005


On 8/30/05, George Styles <ripnetuk at gmail.com> wrote:
> Hi,
> 
> Im grabbing DVB-T transport streams using recent myth cvs. I am then
> encoding them with mencoder to xvid.
> 
> All channels work perfectly (that ive tried) except UK Channel 4. This
> seems to be broadcast with 4 streams within the TS as follows:
> 
> 
> File c4.nuv is an MPEG-2 Transport Stream
> 
> Found PID 0x0000, Program Association Table Stream
> Found PID 0x0010, Other Stream
> Found PID 0x0232, stream id 0xC0 = MPEG Audio Stream 0
> Found PID 0x0230, stream id 0xEA = Video Stream 10
> Found PID 0x0231, stream id 0xC0 = MPEG Audio Stream 0
> Found PID 0x0233, stream id 0xBD = Private Stream 1
> 
> Summary:
> 
> MPEG Transport Packets = 1624357
> PID 0x0000, Program Association Table packets = 811, total bytes = 149224
> PID 0x0010, Other packets = 811, total bytes = 149224
> PID 0x0230, Video stream 10 packets = 1466255, total bytes = 269454132
> PID 0x0231, MPEG Audio stream 0 packets = 112473, total bytes = 20638808
> PID 0x0232, MPEG Audio stream 0 packets = 38228, total bytes = 6880992
> PID 0x0233, Private Stream 1 packets = 5779, total bytes = 1001675
> 
> The PID 231 contains the actual audio for the show, but the PID 232
> seems to contain only silence. Anyone know why C4 broadcast silence?
> is it a different codec? ac3 perhaps?
> 
> Anyway, as sods law would have it, mencoder encodes the second, broken
> audio track, and I end up with a silent movie :(
> 
> Anyone know how to remove a pid from a ts? or maybe just re-label it
> as non-audio so mencoder doesnt pick it up?

George,

I see this on other UK DVB-T channels (BBC1 for instance), usually
silent 64kbps tracks when I've noticed them. I use my Win2K box to do
all my video editing, so remove the track there before creating a DVD
or transcoding to XVID. It's sometimes random which audio track takes
precedence if I forget to remove the silent track before writing to
DVD. I'm not sure if they are 'audio described' tracks (not audio at
all) but transmitted in the stream and decoded by the box.

Nick


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