## General Information

### Scope of this document

This document is aimed to provide information about the v4l2\_codec2 project.
The target readers of this document are the developers and following maintainers
of this project, and the partners who are willing to use the V4L2 components.

### Introduction

v4l2\_codec2 project provides a component implementation of Codec2 framework,
the next-generation codec framework. The component implementation delegates the
request to the driver via the V4L2 API.

## Quick Start Guide

### Prerequisites

*   Gralloc support for graphic buffer allocation
*   ION or Gralloc support for linear buffer allocation
*   Kernel v5.3+ or [this patch][1] backported for buffer identification
*   [V4L2 stateful decoding API](https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/dev-decoder.html)
*   [V4L2 encoding API](https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/dev-encoder.html)
*   Widevine DRM for secure playback

### Enable V4L2 Components

Install the build package and files, and set the parameters in device.mk

```makefile
# Add the folder to the namespace.
PRODUCT_SOONG_NAMESPACES += external/v4l2_codec2

# Add the build target.
PRODUCT_PACKAGES += \
    android.hardware.media.c2@1.0-service-v4l2 \
    libc2plugin_store

# If a customized allocator is needed, then add this package.
# See more detail at "Customized allocator" section.
PRODUCT_PACKAGES += \
    libv4l2_codec2_vendor_allocator

# Install media_codecs_c2.xml.
# The destination is: /vendor/etc/media_codecs_c2.xml
PRODUCT_COPY_FILES += \
    <path_to_file>:$(TARGET_COPY_OUT_VENDOR)/etc/media_codecs_c2.xml

# Set the customized property of v4l2_codec2, including:
# - The maximum concurrent instances for decoder/encoder.
#   It should be the same as "concurrent-instances" at media_codec_c2.xml.
PRODUCT_PROPERTY_OVERRIDES += \
    ro.vendor.v4l2_codec2.decode_concurrent_instances=8 \
    ro.vendor.v4l2_codec2.encode_concurrent_instances=8

# Codec2.0 poolMask:
#   ION(16)
#   BUFFERQUEUE(18)
#   BLOB(19)
#   V4L2_BUFFERQUEUE(20)
#   V4L2_BUFFERPOOL(21)
#   SECURE_LINEAR(22)
#   SECURE_GRAPHIC(23)
#
# For linear buffer allocation:
#   If ION is chosen, then the mask should be 0xf50000
#   If BLOB is chosen, then the mask should be 0xfc0000
PRODUCT_PROPERTY_OVERRIDES += \
    debug.stagefright.c2-poolmask=0xf50000

# Install extended policy for codec2.
# The destination is: /vendor/etc/seccomp_policy/codec2.vendor.ext.policy
PRODUCT_COPY_FILES += \
    <path_to_policy>:$(TARGET_COPY_OUT_VENDOR)/etc/seccomp_policy/codec2.vendor.ext.policy
```

Add decode and encode components in media\_codecs\_c2.xml

```xml
<?xml version="1.0" encoding="utf-8" ?>
<MediaCodecs>
   <Encoders>
       <MediaCodec name="c2.v4l2.avc.encoder" type="video/avc">
           <Limit name="size" min="32x32" max="1920x1088" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" range="1-244800" />
           <Limit name="bitrate" range="1-12000000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-1280x720" range="30-30" />
       </MediaCodec>

       <MediaCodec name="c2.v4l2.vp8.encoder" type="video/x-vnd.on2.vp8">
           <Limit name="size" min="32x32" max="1920x1088" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" range="1-244800" />
           <Limit name="bitrate" range="1-12000000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-1280x720" range="30-30" />
       </MediaCodec>

       <MediaCodec name="c2.v4l2.vp9.encoder" type="video/x-vnd.on2.vp9">
           <Limit name="size" min="32x32" max="1920x1088" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" range="1-244800" />
           <Limit name="bitrate" range="1-12000000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-1280x720" range="30-30" />
       </MediaCodec>
   </Encoders>

   <Decoders>
       <MediaCodec name="c2.v4l2.avc.decoder" type="video/avc" >
           <Limit name="size" min="16x16" max="4096x4096" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" min="1" max="1879200" />
           <Limit name="bitrate" range="1-62500000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-3840x2160" range="30-30" />
           <Feature name="adaptive-playback" />
       </MediaCodec>

       <MediaCodec name="c2.v4l2.vp8.decoder" type="video/x-vnd.on2.vp8" >
           <Limit name="size" min="16x16" max="4096x4096" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" min="1" max="1984500" />
           <Limit name="bitrate" range="1-62500000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-3840x2160" range="30-30" />
           <Feature name="adaptive-playback" />
       </MediaCodec>

       <MediaCodec name="c2.v4l2.vp9.decoder" type="video/x-vnd.on2.vp9" >
           <Limit name="size" min="16x16" max="4096x4096" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" min="1" max="2073600" />
           <Limit name="bitrate" range="1-62500000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-3840x2160" range="30-30" />
           <Feature name="adaptive-playback" />
       </MediaCodec>

       <MediaCodec name="c2.v4l2.avc.decoder.secure" type="video/avc" >
           <Limit name="size" min="16x16" max="4096x4096" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" min="1" max="1879200" />
           <Limit name="bitrate" range="1-62500000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-3840x2160" range="30-30" />
           <Feature name="adaptive-playback" />
           <Feature name="secure-playback" required="true" />
       </MediaCodec>

       <MediaCodec name="c2.v4l2.vp8.decoder.secure" type="video/x-vnd.on2.vp8" >
           <Limit name="size" min="16x16" max="4096x4096" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" min="1" max="1984500" />
           <Limit name="bitrate" range="1-62500000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-3840x2160" range="30-30" />
           <Feature name="adaptive-playback" />
           <Feature name="secure-playback" required="true" />
       </MediaCodec>

       <MediaCodec name="c2.v4l2.vp9.decoder.secure" type="video/x-vnd.on2.vp9" >
           <Limit name="size" min="16x16" max="4096x4096" />
           <Limit name="alignment" value="2x2" />
           <Limit name="block-size" value="16x16" />
           <Limit name="blocks-per-second" min="1" max="2073600" />
           <Limit name="bitrate" range="1-62500000" />
           <Limit name="concurrent-instances" max="8" />
           <Limit name="performance-point-3840x2160" range="30-30" />
           <Feature name="adaptive-playback" />
           <Feature name="secure-playback" required="true" />
       </MediaCodec>
   </Decoders>
</MediaCodecs>
```

Set SELinux file policy in sepolicy/file\_contexts

```
/vendor/bin/hw/android\.hardware\.media\.c2@1\.0-service-v4l2(.*)?  u:object_r:mediacodec_exec:s0
```

Add additional permission in codec2.vendor.ext.policy

```
_llseek: 1
epoll_create1: 1
epoll_ctl: 1
epoll_pwait: 1
eventfd2: 1
fstat64: 1
fstatat64: 1
fstatfs64: 1
getcwd: 1
getdents64: 1
getuid32: 1
mmap2: 1
pselect6: 1
statfs64: 1
sysinfo: 1
ugetrlimit: 1
```

Set file permission in ueventd.rc

```
/dev/video*    0600   media      media
```

### Customized Allocator

The default allocator of the decoder's output buffer is C2AllocatorGralloc.
However, C2AllocatorGralloc might not fit the requirement for secure playback.
In this case, we can implement a customized C2Allocator, and load it at
run-time. Please create a library `libv4l2_codec2_vendor_allocator`, and export
a function `CreateVendorAllocator() `for creating the customized C2Allocator.
Here is an example below.

#### Example of Android.bp

```json
cc_library_shared {
    name: "libv4l2_codec2_vendor_allocator",
    vendor: true,

    defaults: [
        "libcodec2-impl-defaults",
    ],

    srcs: [
        "C2VendorAllocatorFactory.cpp",
    ],

    shared_libs: [
        "libc2plugin_store",
    ],
}
```

#### Example of C2VendorAllocatorFactory.cpp

```cpp
//#define LOG_NDEBUG 0
#define LOG_TAG "C2VendorAllocatorFactory"

#include <C2AllocatorGralloc.h>
#include <utils/Log.h>
#include <v4l2_codec2/plugin_store/V4L2AllocatorId.h>

namespace android {

::C2Allocator* CreateVendorAllocator(::C2Allocator::id_t allocatorId) {
    ALOGV("%s(%d)", __func__, allocatorId);

    // Change to create vendor-customized implementation.
    switch (allocatorId) {
    case V4L2AllocatorId::V4L2_BUFFERQUEUE:
        return new C2AllocatorGralloc(V4L2AllocatorId::V4L2_BUFFERQUEUE, true);
    case V4L2AllocatorId::V4L2_BUFFERPOOL:
        return new C2AllocatorGralloc(V4L2AllocatorId::V4L2_BUFFERPOOL, true);
    case V4L2AllocatorId::SECURE_LINEAR:
        return new C2AllocatorGralloc(V4L2AllocatorId::SECURE_LINEAR, true);
    case V4L2AllocatorId::SECURE_GRAPHIC:
        return new C2AllocatorGralloc(V4L2AllocatorId::SECURE_GRAPHIC, true);
    default:
        ALOGE("%s(): Unknown allocator ID: %d", __func__, allocatorId);
    }
    return nullptr;
}

}  // namespace android

extern "C" ::C2Allocator* CreateAllocator(::C2Allocator::id_t allocatorId) {
    return ::android::CreateVendorAllocator(allocatorId);
}
```

## V4L2 Encoder

### Supported Codecs

Currently the V4L2 encoder has support for the H.264, VP8 and VP9 codecs. Codec
selection can be done by selecting the encoder with the appropriate name.

- H26: *c2.v4l2.avc.encoder*
- VP8: *c2.v4l2.vp8.encoder*
- VP9: *c2.v4l2.vp9.encoder*

### Supported Parameters:

The following parameters are static and can not be changed at run-time:

- *C2_PARAMKEY_PICTURE_SIZE*: This parameter can be used to configure the
resolution of the encoded video stream.
- *C2_PARAMKEY_PROFILE_LEVEL*: This parameter can be used to adjust the desired
profile level. When using the H.264 codec the profile level might be adjusted to
conform to the minimum requirements for the specified bitrate and framerate.
- *C2_PARAMKEY_SYNC_FRAME_INTERVAL*: This parameter can be used to configure the
desired time between subsequent key frames in microseconds.
- *C2_PARAMKEY_BITRATE_MODE*: This parameter can be used to switch between
constant (*C2Config::BITRATE_CONST*) and variable (*C2Config::BITRATE_VARIABLE*)
bitrate modes. When using CBR the encoder will try to maintain a constant
bitrate. This mode is preferable for video conferencing where maintaining a
stable bitrate is more important than quality. When using VBR the encoder will
be allowed to dynamically adjust the bitrate to maintain a constant quality. As
the mediacodec framework does not provide facilities to configure the peak
bitrate when using VBR, it is currently always set to 2x the target bitrate.

The following parameters are dynamic, and can be freely adjusted at run-time:

- *C2_PARAMKEY_BITRATE*: Use this parameter to specify the desired bitrate.
- *C2_PARAMKEY_FRAME_RATE*: This parameter can be used to configure the desired
framerate. Note that the encoder will automatically try to adjust the framerate
if the timestamps on the input video frames don't match the configured
framerate.
- *C2_PARAMKEY_REQUEST_SYNC_FRAME*: This parameter can be used to request
additional key frames in addition to the periodic ones requested through the
*C2_PARAMKEY_SYNC_FRAME_INTERVAL* parameter.

### Supported Input Pixel Formats:

The V4L2 encoder supports various input pixel formats, however frames are
currently always passed to the V4L2 encoder in the NV12 format. If a video frame
using a different pixel format is passed to the encoder, format conversion will
be performed to convert the frame to the NV12 format.

### Additional Features:

To improve the resilience of H.264 video streams when data is missing, SPS and
PPS NAL units are prepended to IDR frames by enabling the
*V4L2_CID_MPEG_VIDEO_PREPEND_SPSPPS_TO_IDR* control. If the V4L2 driver does not
support this control the encoder will manually cache and prepend SPS and PPS NAL
units.

[1]: https://android.googlesource.com/kernel/common/+/ed63bb1d1f8469586006a9ca63c42344401aa2ab