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* DV input/output over IEEE 1394 on OHCI chips
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* Copyright (C)2001 Daniel Maas <dmaas@dcine.com>
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* receive, proc_fs by Dan Dennedy <dan@dennedy.org>
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* video1394.h - driver for OHCI 1394 boards
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* Copyright (C)1999,2000 Sebastien Rougeaux <sebastien.rougeaux@anu.edu.au>
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* Peter Schlaile <udbz@rz.uni-karlsruhe.de>
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* This file is part of FFmpeg.
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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#ifndef AVDEVICE_DV1394_H
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#define AVDEVICE_DV1394_H
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#define DV1394_DEFAULT_CHANNEL 63
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#define DV1394_DEFAULT_CARD 0
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#define DV1394_RING_FRAMES 20
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#define DV1394_WIDTH 720
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#define DV1394_NTSC_HEIGHT 480
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#define DV1394_PAL_HEIGHT 576
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/* This is the public user-space interface. Try not to break it. */
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#define DV1394_API_VERSION 0x20011127
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/* ********************
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There are two methods of operating the DV1394 DV output device.
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The simplest is an interface based on write(): simply write
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full DV frames of data to the device, and they will be transmitted
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as quickly as possible. The FD may be set for non-blocking I/O,
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in which case you can use select() or poll() to wait for output
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To set the DV output parameters (e.g. whether you want NTSC or PAL
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video), use the DV1394_INIT ioctl, passing in the parameters you
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want in a struct dv1394_init.
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To play a raw .DV file: cat foo.DV > /dev/dv1394
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(cat will use write() internally)
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static struct dv1394_init init = {
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0x63, (broadcast channel)
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4, (four-frame ringbuffer)
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DV1394_NTSC, (send NTSC video)
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0, 0 (default empty packet rate)
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ioctl(fd, DV1394_INIT, &init);
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read( <a raw DV file>, buf, DV1394_NTSC_FRAME_SIZE );
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write( <the dv1394 FD>, buf, DV1394_NTSC_FRAME_SIZE );
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For more control over buffering, and to avoid unnecessary copies
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of the DV data, you can use the more sophisticated the mmap() interface.
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First, call the DV1394_INIT ioctl to specify your parameters,
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including the number of frames in the ringbuffer. Then, calling mmap()
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on the dv1394 device will give you direct access to the ringbuffer
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from which the DV card reads your frame data.
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The ringbuffer is simply one large, contiguous region of memory
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containing two or more frames of packed DV data. Each frame of DV data
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is 120000 bytes (NTSC) or 144000 bytes (PAL).
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Fill one or more frames in the ringbuffer, then use the DV1394_SUBMIT_FRAMES
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ioctl to begin I/O. You can use either the DV1394_WAIT_FRAMES ioctl
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or select()/poll() to wait until the frames are transmitted. Next, you'll
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need to call the DV1394_GET_STATUS ioctl to determine which ringbuffer
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frames are clear (ready to be filled with new DV data). Finally, use
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DV1394_SUBMIT_FRAMES again to send the new data to the DV output.
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Example: here is what a four-frame ringbuffer might look like
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during DV transmission:
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frame 0 frame 1 frame 2 frame 3
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*--------------------------------------*
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| CLEAR | DV data | DV data | CLEAR |
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*--------------------------------------*
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transmission goes in this direction --->>>
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The DV hardware is currently transmitting the data in frame 1.
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Once frame 1 is finished, it will automatically transmit frame 2.
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(if frame 2 finishes before frame 3 is submitted, the device
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will continue to transmit frame 2, and will increase the dropped_frames
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counter each time it repeats the transmission).
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If you called DV1394_GET_STATUS at this instant, you would
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receive the following values:
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first_clear_frame = 3
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At this point, you should write new DV data into frame 3 and optionally
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frame 0. Then call DV1394_SUBMIT_FRAMES to inform the device that
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it may transmit the new frames.
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An error (buffer underflow/overflow or a break in the DV stream due
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to a 1394 bus reset) can be detected by checking the dropped_frames
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field of struct dv1394_status (obtained through the
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DV1394_GET_STATUS ioctl).
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The best way to recover from such an error is to re-initialize
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dv1394, either by using the DV1394_INIT ioctl call, or closing the
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file descriptor and opening it again. (note that you must unmap all
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ringbuffer mappings when closing the file descriptor, or else
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dv1394 will still be considered 'in use').
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For maximum efficiency and robustness against bus errors, you are
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advised to model the main loop of your application after the
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following pseudo-code example:
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(checks of system call return values omitted for brevity; always
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check return values in your code!)
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while( frames left ) {
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struct pollfd *pfd = ...;
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pfd->events = POLLOUT | POLLIN; (OUT for transmit, IN for receive)
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(add other sources of I/O here)
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poll(pfd, 1, -1); (or select(); add a timeout if you want)
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struct dv1394_status status;
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ioctl(dv1394_fd, DV1394_GET_STATUS, &status);
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if(status.dropped_frames > 0) {
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for(int i = 0; i < status.n_clear_frames; i++) {
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where copy_DV_frame() reads or writes on the dv1394 file descriptor
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(read/write mode) or copies data to/from the mmap ringbuffer and
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then calls ioctl(DV1394_SUBMIT_FRAMES) to notify dv1394 that new
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frames are availble (mmap mode).
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reset_dv1394() is called in the event of a buffer
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underflow/overflow or a halt in the DV stream (e.g. due to a 1394
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bus reset). To guarantee recovery from the error, this function
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should close the dv1394 file descriptor (and munmap() all
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ringbuffer mappings, if you are using them), then re-open the
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dv1394 device (and re-map the ringbuffer).
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/* maximum number of frames in the ringbuffer */
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#define DV1394_MAX_FRAMES 32
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/* number of *full* isochronous packets per DV frame */
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#define DV1394_NTSC_PACKETS_PER_FRAME 250
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#define DV1394_PAL_PACKETS_PER_FRAME 300
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/* size of one frame's worth of DV data, in bytes */
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#define DV1394_NTSC_FRAME_SIZE (480 * DV1394_NTSC_PACKETS_PER_FRAME)
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#define DV1394_PAL_FRAME_SIZE (480 * DV1394_PAL_PACKETS_PER_FRAME)
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/* ioctl() commands */
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/* I don't like using 0 as a valid ioctl() */
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/* get the driver ready to transmit video.
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pass a struct dv1394_init* as the parameter (see below),
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or NULL to get default parameters */
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/* stop transmitting video and free the ringbuffer */
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/* submit N new frames to be transmitted, where
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the index of the first new frame is first_clear_buffer,
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and the index of the last new frame is
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(first_clear_buffer + N) % n_frames */
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DV1394_SUBMIT_FRAMES,
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/* block until N buffers are clear (pass N as the parameter)
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Because we re-transmit the last frame on underrun, there
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will at most be n_frames - 1 clear frames at any time */
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/* capture new frames that have been received, where
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the index of the first new frame is first_clear_buffer,
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and the index of the last new frame is
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(first_clear_buffer + N) % n_frames */
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DV1394_RECEIVE_FRAMES,
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DV1394_START_RECEIVE,
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/* pass a struct dv1394_status* as the parameter (see below) */
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/* this is the argument to DV1394_INIT */
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/* DV1394_API_VERSION */
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unsigned int api_version;
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/* isochronous transmission channel to use */
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unsigned int channel;
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/* number of frames in the ringbuffer. Must be at least 2
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and at most DV1394_MAX_FRAMES. */
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unsigned int n_frames;
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/* send/receive PAL or NTSC video format */
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enum pal_or_ntsc format;
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/* the following are used only for transmission */
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/* set these to zero unless you want a
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non-default empty packet rate (see below) */
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/* set this to zero unless you want a
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non-default SYT cycle offset (default = 3 cycles) */
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unsigned int syt_offset;
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/* NOTE: you may only allocate the DV frame ringbuffer once each time
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you open the dv1394 device. DV1394_INIT will fail if you call it a
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second time with different 'n_frames' or 'format' arguments (which
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would imply a different size for the ringbuffer). If you need a
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different buffer size, simply close and re-open the device, then
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initialize it with your new settings. */
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/* Q: What are cip_n and cip_d? */
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A: DV video streams do not utilize 100% of the potential bandwidth offered
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by IEEE 1394 (FireWire). To achieve the correct rate of data transmission,
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DV devices must periodically insert empty packets into the 1394 data stream.
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Typically there is one empty packet per 14-16 data-carrying packets.
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Some DV devices will accept a wide range of empty packet rates, while others
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require a precise rate. If the dv1394 driver produces empty packets at
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a rate that your device does not accept, you may see ugly patterns on the
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DV output, or even no output at all.
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The default empty packet insertion rate seems to work for many people; if
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your DV output is stable, you can simply ignore this discussion. However,
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we have exposed the empty packet rate as a parameter to support devices that
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do not work with the default rate.
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The decision to insert an empty packet is made with a numerator/denominator
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algorithm. Empty packets are produced at an average rate of CIP_N / CIP_D.
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You can alter the empty packet rate by passing non-zero values for cip_n
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and cip_d to the INIT ioctl.
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struct dv1394_status {
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/* this embedded init struct returns the current dv1394
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struct dv1394_init init;
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/* the ringbuffer frame that is currently being
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displayed. (-1 if the device is not transmitting anything) */
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/* index of the first buffer (ahead of active_frame) that
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is ready to be filled with data */
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unsigned int first_clear_frame;
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/* how many buffers, including first_clear_buffer, are
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ready to be filled with data */
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unsigned int n_clear_frames;
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/* how many times the DV stream has underflowed, overflowed,
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or otherwise encountered an error, since the previous call
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to DV1394_GET_STATUS */
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unsigned int dropped_frames;
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/* N.B. The dropped_frames counter is only a lower bound on the actual
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number of dropped frames, with the special case that if dropped_frames
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is zero, then it is guaranteed that NO frames have been dropped
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since the last call to DV1394_GET_STATUS.
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#endif /* AVDEVICE_DV1394_H */
added
removed
libavdevice/dv1394.h
