Reconstruction of CBR transport streams
Systems, methods, and devices for generating a constant bitrate (CBR) transport stream in manners that facilitate subsequent reconstruction, and for performing such reconstruction are disclosed herein. For example, generating a CBR transport stream may include for each payload packets: sampling a clock source to obtain a clock sample; and inserting an encoding of the clock sample in a stuffing area of a header of the payload packet. For example, reconstructing a CBR transport stream may include receiving a plurality of packets of a variable bitrate (VBR) transport stream; for a pair of adjacent packets in the VBR transport stream: extracting a clock sample from a header of each of the pair adjacent packets; computing a delta between the clock samples; and inserting one or more null packets between the adjacent packets based on the computed delta and a timing metric corresponding to a bitrate of the CBR transport stream.
1. A computer-implemented method for reconstructing a constant bitrate (CBR) transport stream, the method including:
receiving a plurality of packets of a variable bitrate (VBR) transport stream;
for a pair of adjacent packets in the VBR transport stream:
extracting a clock sample from a header of each of the pair adjacent packets, wherein the clock sample is extracted from a stuffing area of the header, wherein the clock sample is distinct from timing data in a program clock reference (PCR) field of the header, and wherein the stuffing area of the header is distinct from the PCR field of the header;
computing a delta between the clock samples; and
inserting one or more null packets between the adjacent packets based on the computed delta and a timing metric corresponding to a bitrate of the CBR transport stream.
2. The computer-implemented method of claim 1 , wherein a count of the inserted one or more null packets is based on computing a multiple of the delta relative to the timing metric.
3. The computer-implemented method of claim 1 , wherein the stuffing area is located in an adaptation field of the header.
4. The computer-implemented method of claim 1 , wherein said extracting the clock sample includes decoding the clock sample from a type-length-value construct.
5. The computer-implemented method of claim 1 , further comprising detecting a byte sequence in the header indicating that the clock sample is present.
6. The computer-implemented method of claim 1 , further comprising:
estimating the timing metric from a subset of the plurality of packets.
7. The computer-implemented method of claim 6 , wherein said estimating includes determining a minimum delta between adjacent pairs of packets in the subset of the plurality of packets.
8. The computer-implemented method of claim 1 , further comprising reordering packets based on the clock samples.
9. A computer-implemented system for reconstructing a constant bitrate (CBR) transport stream, the system comprising:
at least one processor;
memory in communication with the at least one processor;
software code stored in the memory, which when executed at the at least one processor causes the system to:
for a pair of adjacent packets in a VBR transport stream:
extract a clock sample from a header of each of the adjacent packets, wherein the clock sample is extracted from a stuffing area of the header, wherein the clock sample is distinct from timing data in a program clock reference (PCR) field of the header, and wherein the stuffing area of the header is distinct from the PCR field of the header;
compute a delta between the clock samples; and
insert one or more null packets between the adjacent packets based on the computed delta and a timing metric corresponding to a bitrate of the CBR transport stream.
10. The computer-implemented system of claim 9 , wherein a count of the inserted one or more null packets is based on computing a multiple of the delta relative to the timing metric.
11. The computer-implemented system of claim 9 , wherein the stuffing area is located in an adaptation field of the header.
12. A computer-implemented method for generating a constant bitrate (CBR) transport stream, the method comprising:
for each of a plurality of payload packets:
sampling a clock source to obtain a clock sample; and
inserting an encoding of the clock sample in a stuffing area of a header of the payload packet, wherein the encoding of the clock sample is distinct from timing data in a program clock reference (PCR) field of the header, and wherein the stuffing area of the header is distinct from the PCR field of the header; and
providing the CBR transport stream including the plurality of payload packets.
13. The computer-implemented method of claim 12 , wherein the clock sample is encoded using a type-length-value construct.
14. The computer-implemented method of claim 12 , wherein the clock source is a system clock.
15. The computer-implemented method of claim 14 , wherein the clock sample is a subset of a sample of the system clock.
16. The computer-implemented method of claim 12 , wherein the stuffing area is located in an adaptation field of the header.
17. The computer-implemented method of claim 16 , further comprising:
setting a bit of an adaption field control field of the header.
18. A constant bitrate (CBR) transport stream source comprising:
a clock; and
a packet processor that, for each of a plurality of payload packets, samples a clock source to obtain a clock sample from the clock and inserts the clock sample into a stuffing area of a header of the payload packet, wherein the clock sample is distinct from timing data in a program clock reference (PCR) field of the header, and wherein the stuffing area of the header is distinct from the PCR field of the header; and
a transmitter that transmits a CBR transport stream including the payload packets.
19. The constant bitrate (CBR) transport stream source of claim 18 , wherein the stuffing area is located in an adaptation field of the header.