Repacketizer

The repacketizer can be used to merge multiple Opus packets into a single packet or alternatively to split Opus packets that have previously been merged. Splitting valid Opus packets is always guaranteed to succeed, whereas merging valid packets only succeeds if all frames have the same mode, bandwidth, and frame size, and when the total duration of the merged packet is no more than 120 ms. The 120 ms limit comes from the specification and limits decoder memory requirements at a point where framing overhead becomes negligible. More...

Typedefs
typedef struct OpusRepacketizer	OpusRepacketizer

Functions
int	opus_repacketizer_get_size (void)
	Gets the size of an OpusRepacketizer structure. More...
OpusRepacketizer *	opus_repacketizer_init (OpusRepacketizer *rp)
	(Re)initializes a previously allocated repacketizer state. More...
OpusRepacketizer *	opus_repacketizer_create (void)
	Allocates memory and initializes the new repacketizer with opus_repacketizer_init(). More...
void	opus_repacketizer_destroy (OpusRepacketizer *rp)
	Frees an OpusRepacketizer allocated by opus_repacketizer_create(). More...
int	opus_repacketizer_cat (OpusRepacketizer *rp, const unsigned char *data, opus_int32 len)
	Add a packet to the current repacketizer state. More...
opus_int32	opus_repacketizer_out_range (OpusRepacketizer *rp, int begin, int end, unsigned char *data, opus_int32 maxlen)
	Construct a new packet from data previously submitted to the repacketizer state via opus_repacketizer_cat(). More...
int	opus_repacketizer_get_nb_frames (OpusRepacketizer *rp)
	Return the total number of frames contained in packet data submitted to the repacketizer state so far via opus_repacketizer_cat() since the last call to opus_repacketizer_init() or opus_repacketizer_create(). More...
opus_int32	opus_repacketizer_out (OpusRepacketizer *rp, unsigned char *data, opus_int32 maxlen)
	Construct a new packet from data previously submitted to the repacketizer state via opus_repacketizer_cat(). More...
int	opus_packet_pad (unsigned char *data, opus_int32 len, opus_int32 new_len)
	Pads a given Opus packet to a larger size (possibly changing the TOC sequence). More...
opus_int32	opus_packet_unpad (unsigned char *data, opus_int32 len)
	Remove all padding from a given Opus packet and rewrite the TOC sequence to minimize space usage. More...
int	opus_multistream_packet_pad (unsigned char *data, opus_int32 len, opus_int32 new_len, int nb_streams)
	Pads a given Opus multi-stream packet to a larger size (possibly changing the TOC sequence). More...
opus_int32	opus_multistream_packet_unpad (unsigned char *data, opus_int32 len, int nb_streams)
	Remove all padding from a given Opus multi-stream packet and rewrite the TOC sequence to minimize space usage. More...

Detailed Description

The repacketizer can be used to merge multiple Opus packets into a single packet or alternatively to split Opus packets that have previously been merged. Splitting valid Opus packets is always guaranteed to succeed, whereas merging valid packets only succeeds if all frames have the same mode, bandwidth, and frame size, and when the total duration of the merged packet is no more than 120 ms. The 120 ms limit comes from the specification and limits decoder memory requirements at a point where framing overhead becomes negligible.

The repacketizer currently only operates on elementary Opus streams. It will not manipualte multistream packets successfully, except in the degenerate case where they consist of data from a single stream.

The repacketizing process starts with creating a repacketizer state, either by calling opus_repacketizer_create() or by allocating the memory yourself, e.g.,

OpusRepacketizer *rp;
rp = (OpusRepacketizer*)malloc(opus_repacketizer_get_size());
if (rp != NULL)
    opus_repacketizer_init(rp);

Then the application should submit packets with opus_repacketizer_cat(), extract new packets with opus_repacketizer_out() or opus_repacketizer_out_range(), and then reset the state for the next set of input packets via opus_repacketizer_init().

For example, to split a sequence of packets into individual frames:

unsigned char *data;
int len;
while (get_next_packet(&data, &len))
{
  unsigned char out[1276];
  opus_int32 out_len;
  int nb_frames;
  int err;
  int i;
  err = opus_repacketizer_cat(rp, data, len);
  if (err != OPUS_OK)
  {
    release_packet(data);
    return err;
  }
  nb_frames = opus_repacketizer_get_nb_frames(rp);
  for (i = 0; i < nb_frames; i++)
  {
    out_len = opus_repacketizer_out_range(rp, i, i+1, out, sizeof(out));
    if (out_len < 0)
    {
       release_packet(data);
       return (int)out_len;
    }
    output_next_packet(out, out_len);
  }
  opus_repacketizer_init(rp);
  release_packet(data);
}

Alternatively, to combine a sequence of frames into packets that each contain up to TARGET_DURATION_MS milliseconds of data:

// The maximum number of packets with duration TARGET_DURATION_MS occurs
// when the frame size is 2.5 ms, for a total of (TARGET_DURATION_MS*2/5)
// packets.
unsigned char *data[(TARGET_DURATION_MS*2/5)+1];
opus_int32 len[(TARGET_DURATION_MS*2/5)+1];
int nb_packets;
unsigned char out[1277*(TARGET_DURATION_MS*2/2)];
opus_int32 out_len;
int prev_toc;
nb_packets = 0;
while (get_next_packet(data+nb_packets, len+nb_packets))
{
  int nb_frames;
  int err;
  nb_frames = opus_packet_get_nb_frames(data[nb_packets], len[nb_packets]);
  if (nb_frames < 1)
  {
    release_packets(data, nb_packets+1);
    return nb_frames;
  }
  nb_frames += opus_repacketizer_get_nb_frames(rp);
  // If adding the next packet would exceed our target, or it has an
  // incompatible TOC sequence, output the packets we already have before
  // submitting it.
  // N.B., The nb_packets > 0 check ensures we've submitted at least one
  // packet since the last call to opus_repacketizer_init(). Otherwise a
  // single packet longer than TARGET_DURATION_MS would cause us to try to
  // output an (invalid) empty packet. It also ensures that prev_toc has
  // been set to a valid value. Additionally, len[nb_packets] > 0 is
  // guaranteed by the call to opus_packet_get_nb_frames() above, so the
  // reference to data[nb_packets][0] should be valid.
  if (nb_packets > 0 && (
      ((prev_toc & 0xFC) != (data[nb_packets][0] & 0xFC)) ||
      opus_packet_get_samples_per_frame(data[nb_packets], 48000)*nb_frames >
      TARGET_DURATION_MS*48))
  {
    out_len = opus_repacketizer_out(rp, out, sizeof(out));
    if (out_len < 0)
    {
       release_packets(data, nb_packets+1);
       return (int)out_len;
    }
    output_next_packet(out, out_len);
    opus_repacketizer_init(rp);
    release_packets(data, nb_packets);
    data[0] = data[nb_packets];
    len[0] = len[nb_packets];
    nb_packets = 0;
  }
  err = opus_repacketizer_cat(rp, data[nb_packets], len[nb_packets]);
  if (err != OPUS_OK)
  {
    release_packets(data, nb_packets+1);
    return err;
  }
  prev_toc = data[nb_packets][0];
  nb_packets++;
}
// Output the final, partial packet.
if (nb_packets > 0)
{
  out_len = opus_repacketizer_out(rp, out, sizeof(out));
  release_packets(data, nb_packets);
  if (out_len < 0)
    return (int)out_len;
  output_next_packet(out, out_len);
}

An alternate way of merging packets is to simply call opus_repacketizer_cat() unconditionally until it fails. At that point, the merged packet can be obtained with opus_repacketizer_out() and the input packet for which opus_repacketizer_cat() needs to be re-added to a newly reinitialized repacketizer state.

Typedef Documentation

OpusRepacketizer

typedef struct OpusRepacketizer OpusRepacketizer

Function Documentation

opus_multistream_packet_pad()

int opus_multistream_packet_pad	(	unsigned char *	data,
		opus_int32	len,
		opus_int32	new_len,
		int	nb_streams
	)

Pads a given Opus multi-stream packet to a larger size (possibly changing the TOC sequence).

Parameters

[in,out]	data	const unsigned char*: The buffer containing the packet to pad.
	len	opus_int32: The size of the packet. This must be at least 1.
	new_len	opus_int32: The desired size of the packet after padding. This must be at least 1.
	nb_streams	opus_int32: The number of streams (not channels) in the packet. This must be at least as large as len.

Returns

an error code

Return values

OPUS_OK	on success.
OPUS_BAD_ARG	len was less than 1.
OPUS_INVALID_PACKET	data did not contain a valid Opus packet.

opus_multistream_packet_unpad()

opus_int32 opus_multistream_packet_unpad	(	unsigned char *	data,
		opus_int32	len,
		int	nb_streams
	)

Remove all padding from a given Opus multi-stream packet and rewrite the TOC sequence to minimize space usage.

Parameters

[in,out]	data	const unsigned char*: The buffer containing the packet to strip.
	len	opus_int32: The size of the packet. This must be at least 1.
	nb_streams	opus_int32: The number of streams (not channels) in the packet. This must be at least 1.

Returns

The new size of the output packet on success, or an error code on failure.

Return values

OPUS_BAD_ARG	len was less than 1 or new_len was less than len.
OPUS_INVALID_PACKET	data did not contain a valid Opus packet.

opus_packet_pad()

int opus_packet_pad	(	unsigned char *	data,
		opus_int32	len,
		opus_int32	new_len
	)

Pads a given Opus packet to a larger size (possibly changing the TOC sequence).

Parameters

[in,out]	data	const unsigned char*: The buffer containing the packet to pad.
	len	opus_int32: The size of the packet. This must be at least 1.
	new_len	opus_int32: The desired size of the packet after padding. This must be at least as large as len.

Returns

an error code

Return values

OPUS_OK	on success.
OPUS_BAD_ARG	len was less than 1 or new_len was less than len.
OPUS_INVALID_PACKET	data did not contain a valid Opus packet.

opus_packet_unpad()

opus_int32 opus_packet_unpad	(	unsigned char *	data,
		opus_int32	len
	)

Remove all padding from a given Opus packet and rewrite the TOC sequence to minimize space usage.

Parameters

[in,out]	data	const unsigned char*: The buffer containing the packet to strip.
	len	opus_int32: The size of the packet. This must be at least 1.

Returns

The new size of the output packet on success, or an error code on failure.

Return values

OPUS_BAD_ARG	len was less than 1.
OPUS_INVALID_PACKET	data did not contain a valid Opus packet.

opus_repacketizer_cat()

int opus_repacketizer_cat	(	OpusRepacketizer *	rp,
		const unsigned char *	data,
		opus_int32	len
	)

Add a packet to the current repacketizer state.

This packet must match the configuration of any packets already submitted for repacketization since the last call to opus_repacketizer_init(). This means that it must have the same coding mode, audio bandwidth, frame size, and channel count. This can be checked in advance by examining the top 6 bits of the first byte of the packet, and ensuring they match the top 6 bits of the first byte of any previously submitted packet. The total duration of audio in the repacketizer state also must not exceed 120 ms, the maximum duration of a single packet, after adding this packet.

The contents of the current repacketizer state can be extracted into new packets using opus_repacketizer_out() or opus_repacketizer_out_range().

In order to add a packet with a different configuration or to add more audio beyond 120 ms, you must clear the repacketizer state by calling opus_repacketizer_init(). If a packet is too large to add to the current repacketizer state, no part of it is added, even if it contains multiple frames, some of which might fit. If you wish to be able to add parts of such packets, you should first use another repacketizer to split the packet into pieces and add them individually.

See also

opus_repacketizer_out_range

opus_repacketizer_out

opus_repacketizer_init

Parameters

	rp	OpusRepacketizer*: The repacketizer state to which to add the packet.
[in]	data	const unsigned char*: The packet data. The application must ensure this pointer remains valid until the next call to opus_repacketizer_init() or opus_repacketizer_destroy().
	len	opus_int32: The number of bytes in the packet data.

Returns

An error code indicating whether or not the operation succeeded.

Return values

OPUS_OK	The packet's contents have been added to the repacketizer state.
OPUS_INVALID_PACKET	The packet did not have a valid TOC sequence, the packet's TOC sequence was not compatible with previously submitted packets (because the coding mode, audio bandwidth, frame size, or channel count did not match), or adding this packet would increase the total amount of audio stored in the repacketizer state to more than 120 ms.

opus_repacketizer_create()

OpusRepacketizer* opus_repacketizer_create

(

void

)

Allocates memory and initializes the new repacketizer with opus_repacketizer_init().

opus_repacketizer_destroy()

void opus_repacketizer_destroy

(

OpusRepacketizer *

rp

)

Frees an OpusRepacketizer allocated by opus_repacketizer_create().

Parameters

[in]

rp

OpusRepacketizer*: State to be freed.

opus_repacketizer_get_nb_frames()

int opus_repacketizer_get_nb_frames

(

OpusRepacketizer *

rp

)

Return the total number of frames contained in packet data submitted to the repacketizer state so far via opus_repacketizer_cat() since the last call to opus_repacketizer_init() or opus_repacketizer_create().

This defines the valid range of packets that can be extracted with opus_repacketizer_out_range() or opus_repacketizer_out().

Parameters

rp	OpusRepacketizer*: The repacketizer state containing the frames.

Returns

The total number of frames contained in the packet data submitted to the repacketizer state.

opus_repacketizer_get_size()

int opus_repacketizer_get_size

(

void

)

Gets the size of an OpusRepacketizer structure.

Returns

The size in bytes.

opus_repacketizer_init()

OpusRepacketizer* opus_repacketizer_init

(

OpusRepacketizer *

rp

)

(Re)initializes a previously allocated repacketizer state.

The state must be at least the size returned by opus_repacketizer_get_size(). This can be used for applications which use their own allocator instead of malloc(). It must also be called to reset the queue of packets waiting to be repacketized, which is necessary if the maximum packet duration of 120 ms is reached or if you wish to submit packets with a different Opus configuration (coding mode, audio bandwidth, frame size, or channel count). Failure to do so will prevent a new packet from being added with opus_repacketizer_cat().

See also

opus_repacketizer_create

opus_repacketizer_get_size

opus_repacketizer_cat

Parameters

rp	OpusRepacketizer*: The repacketizer state to (re)initialize.

Returns

A pointer to the same repacketizer state that was passed in.

opus_repacketizer_out()

opus_int32 opus_repacketizer_out	(	OpusRepacketizer *	rp,
		unsigned char *	data,
		opus_int32	maxlen
	)

Construct a new packet from data previously submitted to the repacketizer state via opus_repacketizer_cat().

This is a convenience routine that returns all the data submitted so far in a single packet. It is equivalent to calling

opus_repacketizer_out_range(rp, 0, opus_repacketizer_get_nb_frames(rp),
                            data, maxlen)

Parameters

	rp	OpusRepacketizer*: The repacketizer state from which to construct the new packet.
[out]	data	const unsigned char*: The buffer in which to store the output packet.
	maxlen	opus_int32: The maximum number of bytes to store in the output buffer. In order to guarantee success, this should be at least 1277*opus_repacketizer_get_nb_frames(rp). However, 1*opus_repacketizer_get_nb_frames(rp) plus the size of all packet data submitted to the repacketizer since the last call to opus_repacketizer_init() or opus_repacketizer_create() is also sufficient, and possibly much smaller.

Returns

The total size of the output packet on success, or an error code on failure.

Return values

OPUS_BUFFER_TOO_SMALL

maxlen was insufficient to contain the complete output packet.

opus_repacketizer_out_range()

opus_int32 opus_repacketizer_out_range	(	OpusRepacketizer *	rp,
		int	begin,
		int	end,
		unsigned char *	data,
		opus_int32	maxlen
	)

Construct a new packet from data previously submitted to the repacketizer state via opus_repacketizer_cat().

Parameters

	rp	OpusRepacketizer*: The repacketizer state from which to construct the new packet.
	begin	int: The index of the first frame in the current repacketizer state to include in the output.
	end	int: One past the index of the last frame in the current repacketizer state to include in the output.
[out]	data	const unsigned char*: The buffer in which to store the output packet.
	maxlen	opus_int32: The maximum number of bytes to store in the output buffer. In order to guarantee success, this should be at least 1276 for a single frame, or for multiple frames, 1277*(end-begin). However, 1*(end-begin) plus the size of all packet data submitted to the repacketizer since the last call to opus_repacketizer_init() or opus_repacketizer_create() is also sufficient, and possibly much smaller.

Returns

The total size of the output packet on success, or an error code on failure.

Return values

OPUS_BAD_ARG	[begin,end) was an invalid range of frames (begin < 0, begin >= end, or end > opus_repacketizer_get_nb_frames()).
OPUS_BUFFER_TOO_SMALL	maxlen was insufficient to contain the complete output packet.