demux.tex

linux TV 源码

  using the DMX\_SET\_BUFFER\_SIZE function. If the buffer is not large enough,
  or if the read operations are not performed fast enough, this may result 
  in a buffer overflow error. In this case EOVERFLOW will be returned,
  and the circular buffer will be emptied.
  This call is blocking if there is no data to return, i.e. the process 
  will be put to sleep waiting for data, unless the O\_NONBLOCK flag is 
  specified.\\
  Note that in order to be able to read, the filtering process has to be
  started by defining either a section or a PES filter by means of the 
  ioctl functions, and then starting the filtering process via the DMX\_START
  ioctl function or by setting the DMX\_IMMEDIATE\_START flag.
  If the reading is done from a logical DVR demux device, the data will 
  constitute a Transport Stream including the packets from all PES filters
  in the corresponding demux device /dev/dvb/adapter0/demux0 having the output set 
  to DMX\_OUT\_TS\_TAP.
  }{
  int fd        & File descriptor returned by a previous call to open().\\
  void *buf     & Pointer to the buffer to be used for returned filtered data.\\
  size\_t count  & Size of buf.\\
  }{
  EWOULDBLOCK   & No data to return and O\_NONBLOCK was specified.\\
  EBADF         & fd is not a valid open file descriptor.\\
  ECRC          & Last section had a CRC error - no data returned. 
                  The buffer is flushed.\\
  EOVERFLOW & \\
& The filtered data was not read from the buffer in
                    due time, resulting in non-read data being lost.
                    The buffer is flushed.\\
  ETIMEDOUT       & The section was not loaded within the stated
                    timeout period. See ioctl DMX\_SET\_FILTER for
                    how to set a timeout.\\
  EFAULT          & The driver failed to write to the callers buffer
                    due to an invalid *buf pointer.\\
}

\function{write()}{
  ssize\_t write(int fd, const void *buf, size\_t count);
  }{
  This system call is only provided by the logical device /dev/dvb/adapter0/dvr0, 
  associated with the physical demux device that provides the actual 
  DVR  functionality.  It is used for replay of a digitally recorded 
  Transport Stream. Matching filters have to be defined in the 
  corresponding physical demux device, /dev/dvb/adapter0/demux0.
  The amount of data to be transferred is implied by count.
  }{
  int fd        & File descriptor returned by a previous call to open().\\
  void *buf     & Pointer to the buffer containing the Transport Stream.\\
  size\_t count & Size of buf.\\
  }{
  EWOULDBLOCK   & No data was written. This might happen if
                  O\_NONBLOCK was specified and there is no more
                  buffer space available (if O\_NONBLOCK is not
                  specified the function will block until buffer 
                  space is available).\\
  EBUSY         & This error code indicates that there are
                  conflicting requests. The corresponding demux
                  device is setup to receive data from the front-
                  end. Make sure that these filters are stopped
                  and that the filters with input set to DMX\_IN\_DVR
                  are started.\\
  EBADF         & fd is not a valid open file descriptor.\\
}

\ifunction{DMX\_START}{
  int ioctl( int fd, int request = DMX\_START);
  }{
  This ioctl call is used to start the actual filtering operation 
  defined via the ioctl calls DMX\_SET\_FILTER or DMX\_SET\_PES\_FILTER.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals DMX\_START for this command.\\
  }{
  EBADF  & fd is not a valid file descriptor.\\
  EINVAL & Invalid argument, i.e. no filtering parameters
           provided via the DMX\_SET\_FILTER or
           DMX\_SET\_PES\_FILTER functions.\\
  EBUSY  & This error code indicates that there are
           conflicting requests. There are active filters
           filtering data from another input source. Make
           sure that these filters are stopped before starting
           this filter.\\
}

\ifunction{DMX\_STOP}{
  int ioctl( int fd, int request = DMX\_STOP);
  }{
  This  ioctl call is used to stop the actual filtering operation defined 
  via the ioctl  calls DMX\_SET\_FILTER or DMX\_SET\_PES\_FILTER and started via
  the DMX\_START command.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals DMX\_STOP for this command.\\
  }{
  EBADF  & fd is not a valid file descriptor.\\
}

\ifunction{DMX\_SET\_FILTER}{
  int ioctl( int fd, int request = DMX\_SET\_FILTER, struct dmx\_sct\_filter\_params *params);
  }{
  This ioctl call sets up a filter according to the filter and mask 
  parameters provided. A timeout may be defined stating number of seconds 
  to wait for a section to be loaded. A value of 0 means that no timeout 
  should be applied. Finally there is a flag field where it is possible to
  state whether a section should be CRC-checked, whether the filter should
  be a "one-shot" filter, i.e. if the filtering operation should be stopped
  after the first section is received, and whether the filtering operation 
  should be started immediately (without waiting for a DMX\_START ioctl call).
  If a filter was previously set-up, this filter will be canceled, and the
  receive buffer will be flushed.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals DMX\_SET\_FILTER for this command.\\
  struct dmx\_sct\_filter\_params *params
  & Pointer to structure containing filter parameters.\\
  }{
  EBADF  & fd is not a valid file descriptor.\\
  EINVAL & Invalid argument.\\
}

\ifunction{DMX\_SET\_PES\_FILTER}{
  int ioctl( int fd, int request = DMX\_SET\_PES\_FILTER, 
  struct dmx\_pes\_filter\_params *params);
  }{
  This ioctl call sets up a PES filter according to the parameters provided.
  By a PES filter is meant a filter that is based just on the packet 
  identifier (PID), i.e. no PES header or payload filtering capability is 
  supported.\\
  The transport stream destination for the filtered output may be set. Also
  the PES type may be stated in order to be able to e.g. direct a video 
  stream directly to the video decoder. Finally there is a flag field where
  it is possible to state whether the filtering operation should be started
  immediately (without waiting for a DMX\_START ioctl call).
  If a filter was previously set-up, this filter will be cancelled, and the
  receive buffer will be flushed.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals DMX\_SET\_PES\_FILTER for this command.\\
  struct dmx\_pes\_filter\_params *params
  & Pointer to structure containing filter parameters.\\
  }{
  EBADF  & fd is not a valid file descriptor.\\
  EINVAL & Invalid argument.\\
  EBUSY  & This error code indicates that there are
           conflicting requests. There are active filters
           filtering data from another input source. Make
           sure that these filters are stopped before starting
           this filter.\\
}

\ifunction{DMX\_SET\_BUFFER\_SIZE}{
  int ioctl( int fd, int request = DMX\_SET\_BUFFER\_SIZE, unsigned long size);
  }{
  This ioctl call is used to set the size of the circular buffer used
  for filtered data. The default size is two maximum sized sections, i.e. 
  if this function is not called a buffer size of 2 * 4096 bytes will be
  used.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals DMX\_SET\_BUFFER\_SIZE for this command.\\
  unsigned long size & Size of circular buffer.\\
  }{
  EBADF  & fd is not a valid file descriptor.\\
  ENOMEM & The driver was not able to allocate a buffer of the requested size.\\
}

\ifunction{DMX\_GET\_EVENT}{
  int ioctl( int fd, int request = DMX\_GET\_EVENT, struct dmx\_event *ev);
  }{
  This ioctl call returns an event if available. If an event is not 
  available, the behavior depends on whether the device is in blocking or 
  non-blocking mode.  In the latter case, the call fails immediately with
  errno set to EWOULDBLOCK. In the former case, the call blocks until an
  event becomes available.\\
  The standard Linux poll() and/or select() system calls can be used with
  the device file descriptor to watch for new events.  For select(), the 
  file descriptor should be included in the exceptfds argument, and for 
  poll(), POLLPRI should be specified as the wake-up condition.
  Only the latest event for each filter is saved.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals DMX\_GET\_EVENT for this command.\\
  struct dmx\_event *ev & Pointer to the location where the event is to be stored.\\
  }{
  EBADF  & fd is not a valid file descriptor.\\
  EFAULT & ev points to an invalid address.\\
  EWOULDBLOCK & There is no event pending, and the device is in non-blocking mode.\\
}

\ifunction{DMX\_GET\_STC}{
  int ioctl( int fd, int request = DMX\_GET\_STC, struct dmx\_stc *stc);
  }{
  This ioctl call returns the current value of the system time counter
  (which is driven by a PES filter of type DMX\_PES\_PCR). Some hardware
  supports more than one STC, so you must specify which one by setting
  the num field of stc before the ioctl (range 0...n). The result is returned in form
  of a ratio with a 64 bit numerator and a 32 bit denominator, so the
  real 90kHz STC value is \begin{ttfamily}stc->stc / stc->base\end{ttfamily}.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals DMX\_GET\_STC for this command.\\
  struct dmx\_stc *stc & Pointer to the location where the stc is to be stored.\\
  }{
  EBADF  & fd is not a valid file descriptor.\\
  EFAULT & stc points to an invalid address.\\
  EINVAL & Invalid stc number.\\
}

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