Android 12 Codec2: KEY_PREPEND_HEADER_TO_SYNC_FRAMES

Android 12 introduces a new feature in the Codec2 API called KEY_PREPEND_HEADER_TO_SYNC_FRAMES, which allows developers to prepend codec-specific headers to sync frames. This enhancement provides a more efficient and flexible way of handling sync frames in video codecs.

Introduction

Codec2 is the API used by Android for multimedia encoding and decoding. It provides a unified interface for accessing different multimedia codecs on the device. Android 12 introduces several improvements to the Codec2 API, one of which is the addition of the KEY_PREPEND_HEADER_TO_SYNC_FRAMES option.

What are sync frames?

In video codecs, a sync frame is an independently decodable frame that allows the decoder to resynchronize itself. Sync frames are important for error recovery and seeking operations. They usually occur at regular intervals, providing reference points for decoding subsequent frames.

The need for KEY_PREPEND_HEADER_TO_SYNC_FRAMES

In previous versions of Android, sync frames were sent as regular frames without any additional headers. This approach had limitations, especially when working with codec-specific features or custom codecs. Developers had to handle the synchronization logic separately, leading to suboptimal performance and compatibility issues.

With KEY_PREPEND_HEADER_TO_SYNC_FRAMES, developers can now prepend codec-specific headers to sync frames. This enables:

Improved compatibility with different video codecs: Developers can add specific headers required by a particular codec, accommodating diverse video formats and codecs in a unified manner.
Enhanced codec-specific feature support: Certain codecs require auxiliary data or metadata in sync frames to enable specific features. With the new option, developers can easily include this information within the headers.
Streamlined synchronization process: By including codec-specific headers in sync frames, developers no longer need to manage sync frame detection and handling themselves. The codec will automatically identify and process these frames.

Implementation

To use the KEY_PREPEND_HEADER_TO_SYNC_FRAMES option, follow these steps:

Create an instance of MediaFormat for the desired video format.
Set the KEY_PREPEND_HEADER_TO_SYNC_FRAMES option to true using the setFeatureEnabled() method.
Configure other desired codec-specific parameters using the MediaFormat instance.
Pass the MediaFormat to the MediaCodec for encoding or decoding.

Example code snippet:

MediaFormat format = MediaFormat.createVideoFormat("video/avc", width, height);
format.setFeatureEnabled(MediaFormat.KEY_PREPEND_HEADER_TO_SYNC_FRAMES, true);
format.setInteger(MediaFormat.KEY_BIT_RATE, 800000);
format.setInteger(MediaFormat.KEY_FRAME_RATE, 30);
format.setInteger(MediaFormat.KEY_COLOR_FORMAT, MediaCodecInfo.CodecCapabilities.COLOR_FormatSurface);

MediaCodec codec = MediaCodec.createEncoderByType("video/avc");
codec.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);

Conclusion

Android 12's addition of KEY_PREPEND_HEADER_TO_SYNC_FRAMES in the Codec2 API offers developers an improved approach to handle sync frames in video codecs. By allowing developers to prepend codec-specific headers to sync frames, this enhancement simplifies sync frame management, improves compatibility, and enables better support for codec-specific features. Implementing this option can lead to more efficient video encoding and decoding, benefiting both developers and users alike.

本文来自极简博客，作者：黑暗猎手，转载请注明原文链接：Android 12 Codec2: KEY_PREPEND_HEADER_TO_SYNC_FRAMES