STR (Streaming Data)

CD-ROM data format for streaming movies and other time-series data.

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Overview

Streaming is the reading and processing of successive data from a CD-ROM. STR is the CD-ROM data format defined for streaming on the PlayStation.¹

Streaming is used for animation and audio. It also serves other time-series data that changes continuously.¹

The streaming library is used separately from the other CD-ROM functions.¹

The bitstream for movie playback comes through streaming. The bitstream does not hold the image size, so the STR header holds the data needed for playback.¹

Streaming Data

Streaming data in an STR file is a continuous array of frame data elements.¹

The contents of a frame depend on the data. In an animation, one frame can hold one still image of the sequence.¹

The STR format does not set the data type of a frame.¹

Each frame has its own length and type. One STR file can mix frames of several types and sizes.¹

Frame Data

Frame data is divided into 2048-byte sectors. These match the CD-ROM data sectors.¹

Each sector starts with a 32-byte header. 2016 bytes of data follow.¹

Each frame begins on a sector boundary. The last sector of a frame is padded with dummy data to the 2048-byte boundary.¹²

Sector Header

The sector header is divided into the following fields:²³

All fields are little endian.³

An StTYPE with the MSB set is a system-defined format. With the MSB clear it is a user-defined format, and the other 15 bits are free.²

The streaming library uses StSECTOR_OFFSET, StSECTOR_SIZE and StFRAME_NO to read frame data in order without missing sectors.²

User-defined Frame Data

User-defined data streams with the MSB of StTYPE set to 0.³

A run of streaming data with the same attributes throughout can use one header frame for the whole run. This reduces the total amount of data.³

The manual gives an example of streaming data with a header frame.³

The example is as follows:

In this example the LSB of StTYPE marks the header frame.³

The application can read StTYPE in each frame. The meaning of the frame data can then change with the type of frame.³

A header frame can hold CLUT data that is not saved in each frame. It can also hold a table of jumps to frames.³

MDEC Animation

MDEC animation is a system-defined format with StTYPE 0x8001.⁴

Its sector header has the following fields:

The channel number is 0 for ordinary streaming.⁴

The frame data of an MDEC animation is BS data.

Streaming Data with Audio

The PlayStation plays back ADPCM audio data as specified in the CD-ROM XA standard. Sony calls this XA-ADPCM audio.⁴

XA-ADPCM audio goes from the CD-ROM decoder to the SPU without using main memory. Streaming reads data into main memory, so it cannot play XA-ADPCM audio.⁴

Audio sectors are interleaved with data sectors on the disc. Streaming data with audio places the streaming data in the gaps between the audio sectors.⁴⁵

The manual's example uses streaming data at 30 fps (5 sectors per frame). The audio is 37.8 kHz stereo at double speed.⁵

Sector Size

A sector of ordinary streaming data is 2048 bytes. A sector of streaming data with audio is 2336 bytes.⁶

A data sector has the following parts:

The audio sectors have the following parts:⁶

The CD-ROM XA standard sets the size of the subheader. The subheader holds flags that tell data sectors from audio sectors.⁶

The dummy data makes an audio sector the same size as a data sector.⁶

The sector header and data areas are the same as in ordinary streaming data.⁶

References