[MPlayer-dev-eng] Ac3 streams detected as LPCM or SPU in TS

[Nico Sabbi]

lordvader at swiftdsl.com.au wrote:

>On Sat, 5 Jun 2004 09:15 pm, James Courtier-Dutton wrote:
><snip>
>
>  
>
>>This is a well known problem, and xine has the same problem.
>>1) The DVB card cannot output the PAT or PMT
>>One has to use the DVB API to gather that information.
>>As a result the file saved from that DVB card will not have a PAT or
>>PMT. Really the program saving the file should add PAT and PMT for every
>>10s of the stream before it saves it, but I don't think any linux
>>programs do this currently.
>>    
>>
>
>Something I would like to know, is the lack of PMT/PAT a hardware issue
>(unfixable), or a driver issue (fixable)?
>
>  
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>>2) We are left with TS streams without any PAT or PMT.
>>3) The AC3 is placed in private_stream_1
>>4) The AC3 in private_stream_1 is not in sync with the PES pack.
>>i.e. The beginning of an AC3 pack does not necessarily apprear at the
>>start of a PES pack.
>>
>>Solution:
>>When one starts playing the stream with a private_stream_1, that
>>particular PID should be marked as unidentified.
>>TS pack should be buffered up until 2*AC3 packet length.
>>Once buffered, content detection should be done on the buffered packet.
>>This content detection should probably search the buffer for the AC3
>>header (0x0b, 0x77) and then maybe do a AC3 CRC check on the next 1536
>>bytes. Once identified, all future TS packs can be sent to the AC3 decoder.
>>    
>>
>
>I'll like to have a play around with this approach. I'm not totally
>familair with the way mplayer (or xine) work, but what is sent to the
>audio fifo? Is it the complete packet (ie, the 1536 bytes buffered from
>the dvb packets), or is the 184 bytes received from the dvb input?
>
>  
>

software only: in channels.conf you don't have a way to indicate what 
pid contains the PMT;
I can easily solve it adding always pid 0 (that gives the PMT) in the 
filters and you can add +<pmt_pid>
in one of video/audio fields (as scan indicates extra streams)

>>Problems with this method: -
>>What if the user changed channels while recording. The content of the
>>PID might change from AC3 to subtitles!
>>
>>Cheers
>>James
>>    
>>
>
>Also, I'm not sure if its relevant now, but the file channel9hdtv_ac3.ts
>is successfully uploaded in the incoming ftp directory.
>
>  
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I downloaded that file. This week-end I will try to solve the problem.
    Nico