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Directly calculate the time stamp based on the offset in the stream from 

the first bit in the stream.  This prevents accumulated truncation
errors.

Get the seek offset from file_tell().

svn path=/trunk/; revision=42436
This commit is contained in:
Guy Harris 2012-05-05 02:52:41 +00:00
parent 444187c5e8
commit 1fc695a022
1 changed files with 17 additions and 19 deletions
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36
wiretap/mp2t.c
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@ -58,8 +58,7 @@
typedef struct {
guint32 offset;
struct wtap_nstime now;
int start_offset;
/* length of trailing data (e.g. FEC) that's appended after each packet */
guint8 trailer_len;
} mp2t_filetype_t;
@ -90,7 +89,8 @@ mp2t_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
mp2t = (mp2t_filetype_t*) wth->priv;
*data_offset = mp2t->offset;
*data_offset = file_tell(wth->fh);
/* read only the actual mpeg2 ts packet, not including a trailer */
buffer_assure_space(wth->frame_buffer, MP2T_SIZE);
if (FALSE == mp2t_read_data(buffer_start_ptr(wth->frame_buffer),
@ -105,23 +105,23 @@ mp2t_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)
return FALSE;
}
mp2t->offset += MP2T_SIZE + mp2t->trailer_len;
/* XXX - relative, not absolute, time stamps */
wth->phdr.presence_flags = WTAP_HAS_TS;
/* It would be really cool to be able to configure the bitrate... */
tmp = (MP2T_SIZE+mp2t->trailer_len) * 8;
tmp *= 1000000000;
tmp /= MP2T_QAM256_BITRATE;
/*
* Every packet in an MPEG2-TS stream is has a fixed size of
* MP2T_SIZE plus the number of trailer bytes.
*
* The bitrate is constant, so the time offset, from the beginning
* of the stream, of a given packet is the packet offset, in bits,
* divided by the bitrate.
*
* It would be really cool to be able to configure the bitrate...
*/
tmp = ((guint64)(*data_offset - mp2t->start_offset) * 8); /* offset, in bits */
wth->phdr.ts.secs = tmp / MP2T_QAM256_BITRATE;
wth->phdr.ts.nsecs = (tmp % MP2T_QAM256_BITRATE) * 1000000000 / MP2T_QAM256_BITRATE;
wth->phdr.ts.secs = mp2t->now.secs;
wth->phdr.ts.nsecs = mp2t->now.nsecs;
mp2t->now.nsecs += (guint32)tmp;
if (1000000000 <= mp2t->now.nsecs) {
mp2t->now.nsecs -= 1000000000;
mp2t->now.secs++;
}
wth->phdr.caplen = MP2T_SIZE;
wth->phdr.len = MP2T_SIZE;
@ -229,9 +229,7 @@ mp2t_open(wtap *wth, int *err, gchar **err_info)
}
wth->priv = mp2t;
mp2t->offset = (guint32) first;
mp2t->now.secs = 0;
mp2t->now.nsecs = 0;
mp2t->start_offset = first;
mp2t->trailer_len = trailer_len;
return 1;