demux.tex

linux TV 源码

\devsec{DVB Demux Device}

The DVB demux device controls the filters of the DVB hardware/software.
It can be accessed through \texttt{/dev/adapter0/demux0}.
Data types and and ioctl definitions can be accessed by including
\texttt{linux/dvb/dmx.h} in your application.

\devsubsec{Demux Data Types}


\devsubsubsec{dmx\_output\_t}
\label{dmxoutput}

\begin{verbatim}
typedef enum
{
        DMX_OUT_DECODER,
        DMX_OUT_TAP,
        DMX_OUT_TS_TAP
} dmx_output_t;
\end{verbatim}

\noindent\texttt{DMX\_OUT\_TAP} delivers the stream output to the demux device
on which the ioctl is called.

\noindent\texttt{DMX\_OUT\_TS\_TAP} routes output to the logical DVR device
\texttt{/dev/dvb/adapter0/dvr0}, which delivers a TS multiplexed from
all filters for which \texttt{DMX\_OUT\_TS\_TAP} was specified.


\devsubsubsec{dmx\_input\_t}
\label{dmxinput}

\begin{verbatim}
typedef enum
{
        DMX_IN_FRONTEND,
        DMX_IN_DVR
} dmx_input_t;
\end{verbatim}


\devsubsubsec{dmx\_pes\_type\_t}
\label{dmxpestype}

\begin{verbatim}
typedef enum
{
        DMX_PES_AUDIO,
        DMX_PES_VIDEO,
        DMX_PES_TELETEXT,
        DMX_PES_SUBTITLE,
        DMX_PES_PCR,
        DMX_PES_OTHER
} dmx_pes_type_t;
\end{verbatim}


\devsubsubsec{dmx\_event\_t}
\label{dmxeventt}

\begin{verbatim}
typedef enum
{
        DMX_SCRAMBLING_EV,
        DMX_FRONTEND_EV
} dmx_event_t;
\end{verbatim}


\devsubsubsec{dmx\_scrambling\_status\_t}
\label{dmxscramblingstatus}

\begin{verbatim}
typedef enum
{
        DMX_SCRAMBLING_OFF,
        DMX_SCRAMBLING_ON
} dmx_scrambling_status_t;
\end{verbatim}


\devsubsubsec{struct dmx\_filter}
\label{dmxfilter}

\begin{verbatim}
typedef struct dmx_filter
{
        uint8_t         filter[DMX_FILTER_SIZE];
        uint8_t         mask[DMX_FILTER_SIZE];
} dmx_filter_t;
\end{verbatim}


\devsubsubsec{struct dmx\_sct\_filter\_params}
\label{dmxsctfilterparams}

\begin{verbatim}
struct dmx_sct_filter_params
{
        uint16_t            pid;
        dmx_filter_t        filter;
        uint32_t            timeout;
        uint32_t            flags;
#define DMX_CHECK_CRC       1
#define DMX_ONESHOT         2
#define DMX_IMMEDIATE_START 4
};
\end{verbatim}


\devsubsubsec{struct dmx\_pes\_filter\_params}
\label{dmxpesfilterparams}

\begin{verbatim}
struct dmx_pes_filter_params
{
        uint16_t            pid;
        dmx_input_t         input;
        dmx_output_t        output;
        dmx_pes_type_t      pes_type;
        uint32_t            flags;
};
\end{verbatim}


\devsubsubsec{struct dmx\_event}
\label{dmxevent}

\begin{verbatim}
struct dmx_event
{
        dmx_event_t          event;
        time_t               timeStamp;
        union
        {
                dmx_scrambling_status_t scrambling;
        } u;
};
\end{verbatim}

\devsubsubsec{struct dmx\_stc}
\label{dmxstc}

\begin{verbatim}
struct dmx_stc {
        unsigned int num;       /* input : which STC? 0..N */
        unsigned int base;      /* output: divisor for stc to get 90 kHz clock */
        uint64_t stc;           /* output: stc in 'base'*90 kHz units */
};
\end{verbatim}

\clearpage

\devsubsec{Demux Function Calls}
\function{open()}{
  int open(const char *deviceName, int flags);}{
  This system call, used with a device name of /dev/dvb/adapter0/demux0,
  allocates a new filter 
  and returns a handle which can be used for subsequent control of that 
  filter. This call has to be made for each filter to be used, i.e. every
  returned file descriptor is a reference to a single filter.
  /dev/dvb/adapter0/dvr0 is a logical device to be used for retrieving Transport 
  Streams for digital video recording. When reading from  
  this device a transport stream containing the packets from all PES
  filters set in the corresponding demux device (/dev/dvb/adapter0/demux0) 
  having the output set to DMX\_OUT\_TS\_TAP.  A recorded Transport Stream 
  is replayed by writing to this device.
%  This device can only be opened in read-write mode.

  The significance of blocking or non-blocking mode is described in the
  documentation for functions where there is a difference. It does not 
  affect the semantics of the open() call itself. A device opened in 
  blocking mode can later be put into non-blocking mode
  (and vice versa) using the F\_SETFL command of the fcntl system call.
  }{
  const char *deviceName & Name of demux device.\\
  int flags & A bit-wise OR of the following flags:\\
            & \hspace{1em} O\_RDWR read/write access\\
            & \hspace{1em} O\_NONBLOCK open in non-blocking mode \\
            & \hspace{1em} (blocking mode is the default)\\
  }{
  ENODEV    & Device driver not loaded/available.\\
  EINVAL    & Invalid argument.\\
  EMFILE    & ``Too many open files'', i.e. no more filters available.\\
  ENOMEM    & The driver failed to allocate enough memory.\\
}

\function{close()}{
  int close(int fd);}{
  This system call deactivates and deallocates a filter that was previously
  allocated via the open() call.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  }{
  EBADF & fd is not a valid open file descriptor.\\
}

\function{read()}{
  size\_t read(int fd, void *buf, size\_t count);
  }{
  This system call returns filtered data, which might be section or PES 
  data. The filtered data is transferred from the driver's internal circular
  buffer to buf. The maximum amount of data to be transferred is implied by
  count.\\
  When returning section data the driver always tries to return a complete 
  single section (even though buf would provide buffer space for more data).
  If the size of the buffer is smaller than the section as much as possible
  will be returned, and the remaining data will be provided in subsequent 
  calls.\\
  The size of the internal buffer is 2 * 4096 bytes (the size of two maximum
  sized sections) by default. The size of this buffer may be changed by