Add README.md for split rendering tests

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# IVAS Split Rendering Tests

The IVAS split rendering tests are implemented using `pytest`.

## Overview

The split rendering tests consist of:

* Smoke tests

* BE (bit exact) comparison tests

The tests cover the following IVAS formats:

* Ambisonics

* Multi-Channel

* ISM

* MASA

The tests include both split rendering operating modes:

* Full chain: encoder, decoder, external renderer

* External: external renderer only

Note: MASA format only supports the full chain split rendering mode.

Furthermore, the tests iterate over the following parameters:

* Renderer config file which specifies DoF (degrees of freedom), split rendering bitrate, and split rendering codec

* Trajectory file

* Encoder/decoder bitrate (only for full-chain split rendering mode)

## Directory Structure

```

ivas-codec

├── tests

|   ├── split_rendering

|   |   ├── test_split_rendering.py                 -> split rendering smoke tests

|   |   ├── test_split_rendering_be_comparison.py   -> split rendering BE comparison tests

|   |   ├── constants.py                            -> split rendering constants

|   |   ├── utils.py                                -> split rendering functions

|   |   └── renderer_configs                        -> directory of render config files

|   └── renderer

|       ├── constants.py                            -> renderer constants

|       └── utils.py                                -> renderer functions

└── scripts

    └── trajectories                                -> directory of trajectory files

```

## Running Tests

### Smoke Tests

```bash

python3 -m pytest -n auto -rA tests/split_rendering/test_split_rendering.py

```

### BE Comparison Tests

```bash

python3 -m pytest -n auto -rA tests/split_rendering/test_split_rendering_be_comparison.py

```

## Useful pytest Options

* `-h`: Help options

* `-n N`: Run tests in parallel using `N` processes (requires `pytest-xdist` package)

* `-rA`: Report all test results

* `-k KEYWORD`: Only run tests which match `KEYWORD`

* `--collect-only`: Only collect tests without running them

## Example Commands for Split Rendering

Commands executed for a test can be found from the corresponding test output.

### Full Chain Split Rendering - Ambisonics HOA3

```bash

IVAS_cod -sba 3 512000 48 tests/renderer/data/spectral_test_16ch_48kHz.wav ivas.192

IVAS_dec -T scripts/trajectories/rotate_yaw_pitch_roll1_delayed.csv -render_config tests/split_rendering/renderer_configs/split_renderer_config_3dof_768k_default.txt BINAURAL_SPLIT_CODED 48 ivas.192 split.bit

IVAS_rend -fs 48 -i split.bit -if BINAURAL_SPLIT_CODED -o tests/split_rendering/cut/HOA3_512000bps_rotate_yaw_pitch_roll1_delayed_split_full_rotate_yaw_pitch_roll1__config_split_renderer_config_3dof_768k_default.wav -of BINAURAL -tf scripts/trajectories/rotate_yaw_pitch_roll1.csv

```