ts-demuxer

TS-Demuxer
=====

TS-Demuxer provides an incremental demuxer for MPEG-TS data streams. Basic usage is as follows:

``ts
import { TSDemuxer, ErrCodes } from 'ts-demuxer';

const demuxer = new TSDemuxer((packet) => {
switch (packet.stream_id) {
case 0xE0: / Do stuff with a video packet. / break;
case 0xC0: / Do stuff with an audio packet. / break;
}
});

for (const chunk of / source of data /) {
const err = demuxer.process(chunk);
if (err > 1) throw new Error(${ err }, ${ ErrCodes[err] });
}

demuxer.finalize();
`

The TSDemuxer constructor takes a callback which recieves a packet structure with the following format:

`ts
type Packet = {
data: Uint8Array;
pts: number; // presentation time stamp
dts: number; // decoding time stamp
frame_ticks: number; // time stamp ticks per frame
program: number; // program number (1,2 ...)
stream_number: number; // stream number in program
type: number; // media type / encoding; int -> string mappings in StreamTypes
stream_id: number; // MPEG stream id
content_type: number; // 1 - audio, 2 - video; int -> string mappings in ContentTypes
frame_num: number;
};
`

which can be used to dispatch the data in whatever way is appropriate. This callback is triggered immediately whenever a packet is completed.

The full API is as follows:

`ts
type DemuxOptions = {
copy?: boolean;
};

class TSDemuxer {
offset: number;
readonly pids: Map;
constructor(cb: (p: Packet) => void, opts?: DemuxOptions);
static resync(buffer: Uint8Array, offset?: number): number;
process(buffer: Uint8Array, offset?: number, len?: number): number;
finalize(): void;
}
`

Data is fed to the demuxer via demuxer.process(data: Uint8Array, offset = 0, len = data.length - offset). The chunks do not need to align with packet boundaries; the demuxer will hold on to partial data in between calls, so you can directly feed it with data from, e.g., a node.js readable stream. The first data chunk, however, must be aligned to the start of a packet. To ensure this, the static resync method can be used to find the first offset of the beginning of a packet in a chunk. Once all data has been consumed, it is important to call demuxer.finalize() to let the demuxer know that no more data is coming. One additional packet per multiplexed stream may be emitted at that time, if there is partial packet data left over that has not yet been emitted.

The demuxer.process(data) method returns an integer status code. 0 indicates normal termination; 1 indicates that the last chunk of data ended in the middle of a frame, and more data is expected. Other numbers indicate various errors whose textual explanations can be looked up in the ErrCodes array.

If an error is returned, demuxer.offset will be set to the offset in the data buffer where the last packet for which demuxing was attempted is located. This can be used to try resyncing and continuing demuxing without dropping packets.

By default Packet data will alias the original ArrayBuffers underlying the Uint8Arrays passed into demuxer.process (except where it is necessary to allocate a new buffer to hold packet data the broken across original buffer boundaries). In order to force allocation of new buffers for all packets, construct the TSDemuxer object with the { copy: true } option.

Metadata for individual streams can be inspected during and after demuxing via the readonly demuxer.pids property. The map values are objects of the following form:

`ts
class Stream {
program: number;
id: number;
type: number;
stream_id: number;
content_type: number;
dts: number;
has_dts: boolean;
first_pts: number;
last_pts: number;
has_pts: boolean;
frame_ticks: number;
frame_num: number;
}
``