README: Add a summary of the encoding workflows available.

- Refactor "What is iamf-tools" to include decoding and web demo as separate subsections.
- Clarify that the textproto serves as a config file for iamf-tools encoder.

PiperOrigin-RevId: 686551004

README.md

@@ -9,18 +9,52 @@ The [Immersive Audio Model and Formats](https://aomediacodec.github.io/iamf/)
 
 `iamf-tools` implements tools to help users process and work with the IAMF
 format. These tools can be used as a complement to the `libiamf`
-[reference decoder](https://github.com/AOMediaCodec/libiamf/).
+[reference decoder](https://github.com/AOMediaCodec/libiamf/) and other tools
+such as [ffmpeg](https://ffmpeg.org/).
 
-### Encoder
+
+### Encoding IAMF files
+
+There are multiple workflows for creating IAMF files, supporting different types
+of inputs.
+
+![IAMF encode workflows](docs/iamf-encode-workflows.svg "IAMF encode workflows")
+
+-   [Encode an ADM-BWF file to IAMF](#using-the-encoder-with-adm-bwf-input)
+-   [Encode wav files to IAMF using the iamf-tools
+    encoder](#using-the-encoder-with-wav-files-and-proto-input)
+-   [Encode wav files to IAMF using
+    ffmpeg](docs/external/encoding_with_external_tools.md#encode-wav-files-to-iamf-with-ffmpeg)
+-   [Merge IAMF files and video into an mp4
+    file](docs/external/encoding_with_external_tools.md#merge-an-iamf-file-with-video-into-mp4-using-ffmpeg)
+
+### Decoding IAMF files
+
+The `libiamf` reference decoder is available at
+https://github.com/AOMediaCodec/libiamf/.
+
+###  Web Demo
+
+The [web demo](https://aomediacodec.github.io/iamf-tools/web_demo/) hosted in
+the GitHub Pages of this repo decodes and renders standalone IAMF files to
+stereo and binaural wav files for preview and comparison.
+
+
+## Encoder
 
 The encoder can be used to encode a standalone IAMF Sequence (`.iamf`) file
-based on an ADM-BWF file or an input protocol buffer.
+from a set of multichannel wav files or an ADM-BWF file.
 
-#### Building the encoder
+### Building the encoder
 
 See [Build instructions](docs/build_instructions.md) to build from source.
 
-#### Using the encoder with proto input
+### Using the encoder with wav files and proto input
+
+The `iamf-tools` encoder can be used to encode a set of multichannel wav files
+into an IAMF file. An accompanying input textproto file serves as the
+configuration file, specifying details such as channel layout, mix gains and
+codec to use for the underlying audio elements.
 
 Prepare up to two multichannel wav files and the input textproto file. See
 [Textproto templates](iamf/cli/textproto_templates) for some example input
@@ -43,7 +77,7 @@ bazel-bin/iamf/cli/encoder_main --user_metadata_filename=iamf/cli/testdata/test_
 If this example is successful the encoder will produce an output
 `test_000002.iamf` file in the current directory.
 
-#### Using the encoder with ADM-BWF input
+### Using the encoder with ADM-BWF input
 
 Run the encoder. Specify the input file with `--adm_filename`. See the
 `adm_to_user_metadata` [README.md](iamf/cli/adm_to_user_metadata) for details on
@@ -64,12 +98,6 @@ bazel-bin/iamf/cli/encoder_main --adm_filename=path/to/adm.wav --output_iamf_dir
 The encoder will produce an output `.iamf` file in the output directory, where
 the underlying audio streams are encoded with PCM.
 
-## Web demo
-
-The [web demo](https://aomediacodec.github.io/iamf-tools/web_demo/) hosted in
-the GitHub Pages of this repo decodes and renders standalone IAMF files to
-stereo and binaural wav files for preview and comparison.
-
 ## License
 
 Released under the BSD 3-Clause Clear License. See [LICENSE](LICENSE) for