Method data recorder for recording data packet timestamps
View Patent ↗DVD Rewritable/Re-recordable discs will be used for recording and playing back digital bitstreams, for example MPEG data packets. To enable proper real-time playback of stored MPEG transport packets, a time information is to be added to every data packet to be recorded. A DVD streamer is connected to the application device via an interface, e.g. IEEE 1394. The interface internally uses timestamps having a special format. According to the invention, such interface-generated timestamps are also used for the DVD stream recording, instead of additionally generated independent streamer-specific timestamps. However, a timestamp format conversion is to be carried out because the DVD Streamer timestamp format is different from the IEEE 1394 timestamp format. For such timestamp format conversion differences between consecutive IEEE 1394 timestamps are determined and are used for calculating the DVD stream recording timestamps.
1. Method for data recording using a data recorder converting first data packet timestamps PAT A based on a first clock rate to second data packet timestamps PAT B based on a second clock rate, said clock rates having a ratio B/A, A being derived from said first clock rate and B being derived from said second clock rate, comprised of the following steps:
if no PAT A timestamp wraparound takes place, calculating (μP):
D ( i )=((PAT A ( i )−PAT A ( i− 1))* B+R ( i− 1))/ A
R ( i )=((PAT A ( i )−PAT A ( i− 1))* B+R ( i− 1))mod A;
if a PAT A timestamp wraparound takes place between i−1 and i, calculating (μP):
D ( i )=((PAT A ( i )+PAT — M −PAT A ( i− 1))* B+R ( i− 1))/ A
R ( i )=((PAT A ( i )+PAT — M −PAT A ( i− 1))* B+R ( i− 1))mod A,
wherein PAT B (i)=PAT B (i−1)+D(i)
and wherein (i) denotes a current timestamp (M 1 ), (i−1) denotes a previous timestamp (M 2 ), ‘/’ denotes an integer division, R is a remainder used to avoid the accumulation of rounding errors, and PAT_M is the wraparound value of the timestamp counter of said first clock rate.
2. Method according to claim 1 , wherein an initial value PAT B (0) of said second data packet timestamps PAT B is zero.
3. Method according to claim 1 , wherein said second data packet timestamps PAT B are composed of a basic part PAT BA and an extension part PAT EX and are calculated (μP) according to
PAT EX ( i )=(PAT EX ( i− 1)+ D ( i ))mod 300
PAT BA ( i )=PAT BA ( i− 1)+(PAT EX ( i− 1)+ D ( i ))/300.
4. Method according to claim 1 , wherein the bitlengths of said first and second data packet timestamps are different.
5. Method according to claim 1 , wherein said first timestamps stem from an interface, e.g. an IEEE 1394 interface, and wherein said second timestamps are used for recording data packets on a recorder having included said interface.
6. Data recorder for recording or replaying data packets, using means for converting first data packet timestamps PAT A based on a first clock rate to second data packet timestamps PAT B based on a second clock rate, said clock rates having a ratio B/A, A being derived from said first clock rate and B being derived from said second clock rate, said data recorder including the features:
if no PAT A timestamp wraparound takes place, calculating (μP):
D ( i )=((PAT A ( i )−PAT A ( i− 1))* B+R ( i− 1))/ A
R ( i )=((PAT A ( i )−PAT A ( i− 1))* B+R ( i− 1))mod A
if a PAT A timestamp wraparound takes place between i−1 and i, calculating (μP):
D ( i )=((PAT A ( i )+PAT — M −PAT A ( i− 1))* B+R ( i− 1))/ A
R ( i )=((PAT A ( i )+PAT — M −PAT A ( i− 1))* B+R ( i− 1))mod A,
wherein PAT B (i)=PAT B (i−1)+D(i)
and wherein (i) denotes a current timestamp, (i−1) denotes a previous timestamp, ‘/’ denotes an integer division, R is a remainder used to avoid the accumulation of rounding errors, and PAT_M is the wraparound value of the timestamp counter of said first clock rate.
7. Data recorder according to claim 6 , wherein an initial value PAT B (0) of said second data packet timestamps PAT B is zero.
8. Data recorder according to claim 6 , wherein said second data packet timestamps PAT B are composed of a basic part PAT BA and an extension part PAT EX and are calculated (μP) according to
PAT EX ( i )=(PAT EX ( i− 1)+ D ( i ))mod 300
PAT BA ( i )=PAT BA ( i− 1)+(PAT EX ( i− 1)+ D ( i ))/300.
9. Data recorder according to claim 6 , wherein the bitlengths of said first and second data packet timestamps are different.
10. Data recorder according to claim 6 , wherein said first timestamps stem from an interface, e.g. an IEEE 1394 interface, and wherein said second timestamps are used for recording data packets on said data recorder having included said interface.