![Michael Mann](/assets/img/avatar_default.png)
Bug: 11820 Change-Id: I7e0a603c20ca0c524399beb3d89e14c45dc3a06e Reviewed-on: https://code.wireshark.org/review/12393 Reviewed-by: Michael Mann <mmann78@netscape.net> Petri-Dish: Michael Mann <mmann78@netscape.net> Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org> Reviewed-by: Anders Broman <a.broman58@gmail.com>
415 lines
12 KiB
C
415 lines
12 KiB
C
/* mp2t.c
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*
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* ISO/IEC 13818-1 MPEG2-TS file format decoder for the Wiretap library.
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* Written by Weston Schmidt <weston_schmidt@alumni.purdue.edu>
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* Copyright 2012 Weston Schmidt
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*
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* Wiretap Library
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program 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
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; 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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*/
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#include "config.h"
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#ifdef HAVE_SYS_TYPES_H
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#include <sys/types.h>
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#endif
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#ifdef HAVE_UNISTD_H
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#include <unistd.h>
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#endif
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#include "mp2t.h"
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#include "wtap-int.h"
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#include <wsutil/buffer.h>
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#include "file_wrappers.h"
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#include <errno.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#define MP2T_SYNC_BYTE 0x47
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#define MP2T_SIZE 188
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#define MP2T_QAM64_BITRATE 26970350 /* bits per second */
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#define MP2T_PCR_CLOCK 27000000 /* cycles per second - 27MHz */
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/* we try to detect trailing data up to 40 bytes after each packet */
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#define TRAILER_LEN_MAX 40
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/* number of consecutive packets we must read to decide that a file
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is actually an mpeg2 ts */
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#define SYNC_STEPS 10
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typedef struct {
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guint32 start_offset;
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guint64 bitrate;
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/* length of trailing data (e.g. FEC) that's appended after each packet */
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guint8 trailer_len;
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} mp2t_filetype_t;
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static gboolean
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mp2t_read_packet(mp2t_filetype_t *mp2t, FILE_T fh, gint64 offset,
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struct wtap_pkthdr *phdr, Buffer *buf, int *err,
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gchar **err_info)
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{
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guint64 tmp;
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ws_buffer_assure_space(buf, MP2T_SIZE);
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if (!wtap_read_bytes_or_eof(fh, ws_buffer_start_ptr(buf), MP2T_SIZE, err, err_info))
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return FALSE;
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phdr->rec_type = REC_TYPE_PACKET;
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/* XXX - relative, not absolute, time stamps */
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phdr->presence_flags = WTAP_HAS_TS;
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/*
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* Every packet in an MPEG2-TS stream is has a fixed size of
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* MP2T_SIZE plus the number of trailer bytes.
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*
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* We assume that the bits in the transport stream are supplied at
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* a constant rate; is that guaranteed by all media that use
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* MPEG2-TS? If so, the time offset, from the beginning of the
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* stream, of a given packet is the packet offset, in bits, divided
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* by the bitrate.
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*
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* It would be really cool to be able to configure the bitrate, in
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* case our attempt to guess it from the PCRs of one of the programs
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* doesn't get the right answer.
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*/
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tmp = ((guint64)(offset - mp2t->start_offset) * 8); /* offset, in bits */
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phdr->ts.secs = (time_t)(tmp / mp2t->bitrate);
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phdr->ts.nsecs = (int)((tmp % mp2t->bitrate) * 1000000000 / mp2t->bitrate);
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phdr->caplen = MP2T_SIZE;
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phdr->len = MP2T_SIZE;
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return TRUE;
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}
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static gboolean
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mp2t_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
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{
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mp2t_filetype_t *mp2t;
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mp2t = (mp2t_filetype_t*) wth->priv;
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*data_offset = file_tell(wth->fh);
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if (!mp2t_read_packet(mp2t, wth->fh, *data_offset, &wth->phdr,
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wth->frame_buffer, err, err_info)) {
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return FALSE;
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}
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/* if there's a trailer, skip it and go to the start of the next packet */
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if (mp2t->trailer_len!=0) {
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if (-1 == file_seek(wth->fh, mp2t->trailer_len, SEEK_CUR, err)) {
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return FALSE;
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}
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}
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return TRUE;
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}
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static gboolean
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mp2t_seek_read(wtap *wth, gint64 seek_off, struct wtap_pkthdr *phdr,
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Buffer *buf, int *err, gchar **err_info)
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{
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mp2t_filetype_t *mp2t;
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if (-1 == file_seek(wth->random_fh, seek_off, SEEK_SET, err)) {
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return FALSE;
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}
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mp2t = (mp2t_filetype_t*) wth->priv;
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if (!mp2t_read_packet(mp2t, wth->random_fh, seek_off, phdr, buf,
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err, err_info)) {
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if (*err == 0)
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*err = WTAP_ERR_SHORT_READ;
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return FALSE;
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}
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return TRUE;
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}
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static guint64
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mp2t_read_pcr(guint8 *buffer)
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{
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guint64 base;
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guint64 ext;
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base = pntoh40(buffer);
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base >>= 7;
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ext = pntoh16(&buffer[4]);
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ext &= 0x01ff;
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return (base * 300 + ext);
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}
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/*
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* XXX - should we limit this to a fixed number of frames, rather than
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* potentially scanning the entire file for a PCR?
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*/
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static gboolean
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mp2t_find_next_pcr(wtap *wth, guint8 trailer_len,
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int *err, gchar **err_info, guint32 *idx, guint64 *pcr, guint16 *pid)
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{
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guint8 buffer[MP2T_SIZE+TRAILER_LEN_MAX];
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gboolean found;
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guint8 afc;
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found = FALSE;
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while (FALSE == found) {
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(*idx)++;
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if (!wtap_read_bytes_or_eof(
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wth->fh, buffer, MP2T_SIZE+trailer_len, err, err_info)) {
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/* Read error, short read, or EOF */
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return FALSE;
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}
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if (MP2T_SYNC_BYTE != buffer[0]) {
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continue;
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}
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/* Read out the AFC value. */
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afc = 3 & (buffer[3] >> 4);
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if (afc < 2) {
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continue;
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}
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/* Check the length. */
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if (buffer[4] < 7) {
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continue;
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}
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/* Check that there is the PCR flag. */
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if (0x10 != (0x10 & buffer[5])) {
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continue;
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}
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/* We have a PCR value! */
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*pcr = mp2t_read_pcr(&buffer[6]);
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*pid = 0x01ff & pntoh16(&buffer[1]);
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found = TRUE;
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}
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return TRUE;
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}
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static wtap_open_return_val
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mp2t_bits_per_second(wtap *wth, guint32 first, guint8 trailer_len,
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guint64 *bitrate, int *err, gchar **err_info)
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{
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guint32 pn1, pn2;
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guint64 pcr1, pcr2;
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guint16 pid1, pid2;
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guint32 idx;
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guint64 pcr_delta, bits_passed;
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/* Find the first PCR + PID.
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* Then find another PCR in that PID.
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* Take the difference and that's our bitrate.
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* All the different PCRs in different PIDs 'should' be the same.
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*
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* XXX - is this assuming that the time stamps in the PCRs correspond
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* to the time scale of the underlying transport stream?
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*/
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idx = first;
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if (!mp2t_find_next_pcr(wth, trailer_len, err, err_info, &idx, &pcr1, &pid1)) {
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/* Read error, short read, or EOF */
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if (*err == WTAP_ERR_SHORT_READ)
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return WTAP_OPEN_NOT_MINE; /* not a full frame */
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if (*err != 0)
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return WTAP_OPEN_ERROR;
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/* We don't have any PCRs, so we can't guess the bit rate.
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* Default to something reasonable.
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*/
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*bitrate = MP2T_QAM64_BITRATE;
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return WTAP_OPEN_MINE;
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}
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pn1 = idx;
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pn2 = pn1;
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while (pn1 == pn2) {
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if (!mp2t_find_next_pcr(wth, trailer_len, err, err_info, &idx, &pcr2, &pid2)) {
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/* Read error, short read, or EOF */
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if (*err == WTAP_ERR_SHORT_READ)
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return WTAP_OPEN_NOT_MINE; /* not a full frame */
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if (*err != 0)
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return WTAP_OPEN_ERROR;
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/* We don't have two PCRs for the same PID, so we can't guess
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* the bit rate.
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* Default to something reasonable.
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*/
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*bitrate = MP2T_QAM64_BITRATE;
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return WTAP_OPEN_MINE;
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}
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if (pid1 == pid2) {
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pn2 = idx;
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}
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}
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if (pcr2 <= pcr1) {
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/* The PCRs for that PID didn't go forward; treat that as an
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* indication that this isn't an MPEG-2 TS.
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*/
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return WTAP_OPEN_NOT_MINE;
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}
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pcr_delta = pcr2 - pcr1;
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bits_passed = MP2T_SIZE * (pn2 - pn1) * 8;
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*bitrate = ((MP2T_PCR_CLOCK * bits_passed) / pcr_delta);
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if (*bitrate == 0) {
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/* pcr_delta < MP2T_PCR_CLOCK * bits_passed (pn2 != pn1,
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* as that's the test for the loop above, so bits_passed
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* is non-zero).
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*
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* That will produce a fractional bitrate, which turns
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* into zero, causing a zero divide later.
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*
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* XXX - should we report this as "not ours"? A bitrate
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* of less than 1 bit per second is not very useful for any
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* form of audio/video, so presumably that's unlikely to
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* be an MP2T file.
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*/
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return WTAP_OPEN_ERROR;
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}
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return WTAP_OPEN_MINE;
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}
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wtap_open_return_val
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mp2t_open(wtap *wth, int *err, gchar **err_info)
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{
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guint8 buffer[MP2T_SIZE+TRAILER_LEN_MAX];
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guint8 trailer_len = 0;
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guint sync_steps = 0;
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guint i;
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guint32 first = 0;
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mp2t_filetype_t *mp2t;
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wtap_open_return_val status;
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guint64 bitrate;
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if (!wtap_read_bytes(wth->fh, buffer, MP2T_SIZE, err, err_info)) {
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if (*err != WTAP_ERR_SHORT_READ)
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return WTAP_OPEN_ERROR;
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return WTAP_OPEN_NOT_MINE;
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}
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for (i = 0; i < MP2T_SIZE; i++) {
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if (MP2T_SYNC_BYTE == buffer[i]) {
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first = i;
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goto found;
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}
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}
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/*
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* No sync bytes found, so not an MPEG-2 Transport Stream file.
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*/
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return WTAP_OPEN_NOT_MINE; /* wrong file type - not an mpeg2 ts file */
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found:
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if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
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return WTAP_OPEN_ERROR;
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}
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/* read some packets and make sure they all start with a sync byte */
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do {
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if (!wtap_read_bytes(wth->fh, buffer, MP2T_SIZE+trailer_len, err, err_info)) {
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if (*err != WTAP_ERR_SHORT_READ)
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return WTAP_OPEN_ERROR; /* read error */
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if(sync_steps<2) return WTAP_OPEN_NOT_MINE; /* wrong file type - not an mpeg2 ts file */
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break; /* end of file, that's ok if we're still in sync */
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}
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if (buffer[0] == MP2T_SYNC_BYTE) {
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sync_steps++;
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}
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else {
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/* no sync byte found, check if trailing data is appended
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and we have to increase the packet size */
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/* if we've already detected a trailer field, we must remain in sync
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another mismatch means we have no mpeg2 ts file */
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if (trailer_len>0)
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return WTAP_OPEN_NOT_MINE;
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/* check if a trailer is appended to the packet */
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for (i=0; i<TRAILER_LEN_MAX; i++) {
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if (buffer[i] == MP2T_SYNC_BYTE) {
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trailer_len = i;
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if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
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return WTAP_OPEN_ERROR;
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}
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sync_steps = 0;
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break;
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}
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}
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/* no sync byte found in the vicinity, this is no mpeg2 ts file */
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if (i==TRAILER_LEN_MAX)
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return WTAP_OPEN_NOT_MINE;
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}
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} while (sync_steps < SYNC_STEPS);
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if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
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return WTAP_OPEN_ERROR;
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}
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/* Ensure there is a valid bitrate */
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status = mp2t_bits_per_second(wth, first, trailer_len,
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&bitrate, err, err_info);
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if (status != WTAP_OPEN_MINE) {
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return status;
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}
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if (-1 == file_seek(wth->fh, first, SEEK_SET, err)) {
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return WTAP_OPEN_ERROR;
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}
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wth->file_type_subtype = WTAP_FILE_TYPE_SUBTYPE_MPEG_2_TS;
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wth->file_encap = WTAP_ENCAP_MPEG_2_TS;
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wth->file_tsprec = WTAP_TSPREC_NSEC;
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wth->subtype_read = mp2t_read;
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wth->subtype_seek_read = mp2t_seek_read;
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wth->snapshot_length = 0;
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mp2t = (mp2t_filetype_t*) g_malloc(sizeof(mp2t_filetype_t));
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wth->priv = mp2t;
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mp2t->start_offset = first;
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mp2t->trailer_len = trailer_len;
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mp2t->bitrate = bitrate;
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return WTAP_OPEN_MINE;
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}
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/*
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* Editor modelines - http://www.wireshark.org/tools/modelines.html
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*
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* Local variables:
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* c-basic-offset: 4
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* tab-width: 8
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* indent-tabs-mode: nil
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* End:
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*
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* vi: set shiftwidth=4 tabstop=8 expandtab:
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* :indentSize=4:tabSize=8:noTabs=true:
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*/
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