DVB Demux Device

Demux Function Calls

open() DESCRIPTION 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. 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. SYNOPSIS int open(const char ⋆deviceName, int flags); PARAMETERS const char *deviceName Name of demux device. int flags A bit-wise OR of the following flags: O_RDWR read/write access O_NONBLOCK open in non-blocking mode (blocking mode is the default) RETURN VALUE 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.

close() DESCRIPTION This system call deactivates and deallocates a filter that was previously allocated via the open() call. SYNOPSIS int close(int fd); PARAMETERS int fd File descriptor returned by a previous call to open(). RETURN VALUE EBADF fd is not a valid open file descriptor.

read() DESCRIPTION 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 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. SYNOPSIS size_t read(int fd, void ⋆buf, size_t count); PARAMETERS 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. RETURN VALUE 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.

write() DESCRIPTION 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. SYNOPSIS ssize_t write(int fd, const void ⋆buf, size_t count); PARAMETERS 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. RETURN VALUE 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.

DMX_START DESCRIPTION This ioctl call is used to start the actual filtering operation defined via the ioctl calls DMX_SET_FILTER or DMX_SET_PES_FILTER. SYNOPSIS int ioctl( int fd, int request = DMX_START); PARAMETERS int fd File descriptor returned by a previous call to open(). int request Equals DMX_START for this command. &return-value-dvb; 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.

DMX_STOP DESCRIPTION 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. SYNOPSIS int ioctl( int fd, int request = DMX_STOP); PARAMETERS int fd File descriptor returned by a previous call to open(). int request Equals DMX_STOP for this command. &return-value-dvb;

DMX_SET_FILTER DESCRIPTION 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. SYNOPSIS int ioctl( int fd, int request = DMX_SET_FILTER, struct dmx_sct_filter_params ⋆params); PARAMETERS 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. &return-value-dvb;

DMX_SET_PES_FILTER DESCRIPTION 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. SYNOPSIS int ioctl( int fd, int request = DMX_SET_PES_FILTER, struct dmx_pes_filter_params ⋆params); PARAMETERS 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. &return-value-dvb; 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.

DMX_SET_BUFFER_SIZE DESCRIPTION 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. SYNOPSIS int ioctl( int fd, int request = DMX_SET_BUFFER_SIZE, unsigned long size); PARAMETERS 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. &return-value-dvb;

DMX_GET_EVENT DESCRIPTION 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. SYNOPSIS int ioctl( int fd, int request = DMX_GET_EVENT, struct dmx_event ⋆ev); PARAMETERS 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. &return-value-dvb; EWOULDBLOCK There is no event pending, and the device is in non-blocking mode.

DMX_GET_STC DESCRIPTION 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 stc->stc / stc->base . SYNOPSIS int ioctl( int fd, int request = DMX_GET_STC, struct dmx_stc ⋆stc); PARAMETERS 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. &return-value-dvb; EINVAL Invalid stc number.

DMX_GET_PES_PIDS DESCRIPTION This ioctl is undocumented. Documentation is welcome. SYNOPSIS int ioctl(fd, int request = DMX_GET_PES_PIDS, __u16[5]); PARAMETERS int fd File descriptor returned by a previous call to open(). int request Equals DMX_GET_PES_PIDS for this command. __u16[5] Undocumented. &return-value-dvb;

DMX_GET_CAPS DESCRIPTION This ioctl is undocumented. Documentation is welcome. SYNOPSIS int ioctl(fd, int request = DMX_GET_CAPS, dmx_caps_t *); PARAMETERS int fd File descriptor returned by a previous call to open(). int request Equals DMX_GET_CAPS for this command. dmx_caps_t * Undocumented. &return-value-dvb;

DMX_SET_SOURCE DESCRIPTION This ioctl is undocumented. Documentation is welcome. SYNOPSIS int ioctl(fd, int request = DMX_SET_SOURCE, dmx_source_t *); PARAMETERS int fd File descriptor returned by a previous call to open(). int request Equals DMX_SET_SOURCE for this command. dmx_source_t * Undocumented. &return-value-dvb;

DMX_ADD_PID DESCRIPTION This ioctl is undocumented. Documentation is welcome. SYNOPSIS int ioctl(fd, int request = DMX_ADD_PID, __u16 *); PARAMETERS int fd File descriptor returned by a previous call to open(). int request Equals DMX_ADD_PID for this command. __u16 * Undocumented. &return-value-dvb;

DMX_REMOVE_PID DESCRIPTION This ioctl is undocumented. Documentation is welcome. SYNOPSIS int ioctl(fd, int request = DMX_REMOVE_PID, __u16 *); PARAMETERS int fd File descriptor returned by a previous call to open(). int request Equals DMX_REMOVE_PID for this command. __u16 * Undocumented. &return-value-dvb;