Simple and efficient multicast and transport stream manipulation

Welcome to Multicat!

The multicat package contains a set of tools designed to easily and
efficiently manipulate multicast streams in general, and MPEG-2
Transport Streams (ISO/IEC 13818-1) in particular.

The multicat tool itself is a 1 input/1 output application. Inputs and
outputs can be network streams (unicast and multicast, IPv4 and IPv6), files,
directories, character devices or FIFOs. Typical applications are recording
live transport streams, or playing out TS files without modification.

Multicat tries to rebuild the internal clock of the input stream; but
it wants to remain agnostic of what is transported, so in case of files
or directories, the said clock is stored to an auxiliary file (example.aux
accompanies example.ts) while recording. Other inputs are considered "live",
and the input clock is simply derived from the reception time of the

IngesTS is a companion application designed to manipulate TS files. It
reads the PCR values of the file, and builds the auxiliary file that is
necessary for multicat.

OffseTS is another companion application to manipulate auxiliary files.
Given an offset in time from the beginning of the file, it returns the offset
of the position in number of packets. It is currently deprecated in favour of
using the -k and -d options of multicat.

LasTS is also a companion application which gives the total duration of an
auxiliary file.

Finally aggregaRTP and reordeRTP can be used to carry a high-bitrate
signal over one or several contribution links, and support retransmission
of lost packets via an additional UDP or TCP connection. ReordeRTP can also
smooth up the reception of a stream from a link that is known to reorder
and add jitter to packets.

The multicat suite of applications is very lightweight and designed to
operate in tight environments. Memory and CPU usages are kept to a minimum,
and they feature only one thread of execution.

The socket description format

For conveniency all tools use the same way of describing a socket in a
program argument:

<connect address>:<connect port>@<bind address>:<bind port>/<options>

All parts are optional; default port (1234) or wildcard address will then
be used.

Some examples:

Reading all streams coming to port 5004:
Reading from a multicast stream on port 5004:
The same, with source-specific multicast:
Writing to a multicast stream on port 5004:
The same, but binding to a specific interface:

Options include:
 /ifindex=X (binds to a specific network interface, by link number)
 /ifaddr=XXX.XXX.XXX.XXX (binds to a specific network interface, by address)
 /ttl=XX (time-to-live of the UDP packet)
 /tos=XX (sets the IPv4 Type Of Service option)
 /tcp (binds a TCP socket instead of UDP)
 /srcaddr=XXX.XXX.XXX.XXX (source address for raw packets)
 /srcportr=XX (source port for raw packets)


Also, multicat supports IPv6 addresses.

Basic uses

Recording a multicast address to a file:

multicat @ /tmp/myfile.ts

This will also create file /tmp/myfile.aux. Playing back the file:

multicat -p 68 /tmp/myfile.ts

Adding an RTP header to an existing multicast stream:

multicat -p 68 -u @

The PCR PID is here supposed to be 68. If you don't specify it, the timestamps
will not be RFC-compliant (but will work in most cases). You can use the
mpeg_print_pcr example from biTStream to determine it. Otherwise, if you are
sure the stream contains a single program, and only one PID carries a PCR, you
can pass "-p 8192" the disable the PID check. This isn't on by default because
it can produce awful things with multi-program transport streams, and the
world would be a better place if people had to knowingly turn it on.

Starting at a given position for a given duration:

multicat -p 68 -k 270000000 -d 2700000000 /tmp/myfile.ts

In this case multicat discards the first 10 seconds, and only plays the file
for 100 seconds. Internally multicat uses a 27 MHz monotonic clock, and all
offsets (starting from 0) and durations are expressed in this unit.

Making an extract of a recorded file to a plain TS file:

multicat -f -k 270000000 -d 2700000000 /tmp/myfile.ts /tmp/extract.ts

The option -f allows outputting the extract as fast as the output item can
write it, without reproducing the same pace as the original stream (and thus,
waiting 100 seconds).

Using IngesTS

ingests -p 68 /tmp/afile.ts

This will create file /tmp/afile.aux. 68 is supposed to be the PCR PID.
The same note as above applies to ingesTS.

Playing the file:

multicat -p 68 /tmp/afile.ts

Working with directories

Starting with version 2.0, multicat can write or read a continuous stream to
discontinuous buffers, while still retaining the original properties. For

mkdir mydir
multicat @ mydir

creates file XXXXXX.ts and XXXXXX.aux in mydir. Every hour, multicat closes
both files, and creates (XXXXXX+1).ts and (XXXXXX+1).aux. And so one. The
stream can then be identically replayed with a 100 seconds delay with:

multicat -p 68 -k -2700000000 mydir

A negative value to -k implies "from the end", in this case from the present
time. To make an extract of the stream:

multicat -f -k 35383033980000000 -d 27000000000 mydir extract.ts

With the directory input/output, timestamps represent the number of ticks of
a 27 MHz real-time clock since the 1st of January 1970 (UNIX Epoch). It is
therefore possible to pass absolute (positive) dates to -k.

There is no built-in expiration of files in multicat; to avoid filling up the
partition, it is necessary to run multicat_expire.sh every hour.

The duration of the segments may be specified with -r. It is also advised to
add an offset with -O (typically a per-stream random number of up to the
segment duration minus one) to avoid having all multicat processes rotate
files exactly at the same time, resulting in a surge in CPU usage and disk I/O.

Using OffseTS

We want to take the first 60 minutes of a TS file. We must scale it in a
27 MHz clock:
60 * 60 (seconds) * 27000000 (MHz) = 97200000000

Find the offset in 1316-blocks:

offsets /tmp/myfile.aux 97200000000

It returns for instance "556896". Then cut the file using dd:

dd if=/tmp/myfile.ts of=/tmp/mynewfile.ts bs=1316 count=556896

Alternatively, if we want to *remove* the first hour:

dd if=/tmp/myfile.ts of=/tmp/mynewfile.ts bs=1316 skip=556896

It can also be done with multicat using the -s and -n options.

OffseTS is currently deprecated in favour of using the -k and -d options of
the multicat program. OffseTS is still distributed for compatibility, but
doesn't support the new directory input.

Using AggregaRTP and ReordeRTP

Splitting an RTP stream to two streams with different routing policies:

aggregartp @

At the other end, reassembling the two streams into one usable stream:


Transmit a signal over a lossy link:

aggregartp @ -X @:5006
reordertp @ -X

The same, but using inverted TCP for retransmission (for NAT traversal for
reordertp @ -X @:5006/tcp
aggregartp @ -X

(with TCP the listener must be started before the other)