WebRTC资讯：H265支持进展

目前H265应用越来越广泛，很多设备都支持硬件加速的H265编解码。作为最常见的音视频终端，Chrome在过去一直都没有H265支持的，毕竟不是AV1那样的亲儿子。人们为了让Chrome完整支持H265，用上了各种招式，例如传输上，用到了datachannel/WebTransport传输H265码流，解码上用到了wasm。

在Native端，要支持H265，得自己魔改WebRTC代码，例如第三方开源WebRTC库：Intel的OWT。现在这些状况就要改变了，目前Chrome已经支持H265硬解，WebRTC上也开始进行H265支持的开发，这一切都要从这个讨论开始：
Issue 41480904:Unblock Chrome platform support of H.265 (including H26xPacketBuffer)，提到目前很多安防摄像机都是默认H265编码，修改为H264代价太高，大概率是国人提的需求😀。

目前WebRTC中H265代码由Intel团队的人提交，跟Intel自己的开源WebRTC库OWT中代码相似。目前代码中（截至2023.9.20）中主要三个提交，增加了H265 Nalu的解析，SDP中相关定义，RTP包处理/编解码器相关预留H265坑位，离实际能使用还有很多事情要做，如果感兴趣，也可以先看下Intel OWT中的H265代码，代码中搜索OWT_ENABLE_H265字段，就可以看到H265相关。本文后续也将继续跟踪H265进展。

2025-03-12代码更新

Revert the deletion of WebRTC-VideoH26xPacketBuffer flag

Revert the deletion of WebRTC-VideoH26xPacketBuffer flag.
This unlaunches the experiment for H264 due to issues reported for H264
where the old packet buffer behaves better than the new one. A recently
introduced issue will be fixed separately from this CL and rollout
restarted.
This CL is not a clean revert though (see delta with PS#1):
we will continue to use the H26xPacketBuffer for the new codec H265
because it does not work with the old packet buffer anyway.
Bug: webrtc:41480904
Change-Id: Icac49fa70f1c78d1ed596a7838d1417f6588a8b4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/380861
Reviewed-by: Evan Shrubsole <eshr@webrtc.org>
Reviewed-by: Jianlin Qiu <jianlin.qiu@intel.com>

Revert the deletion of WebRTC-VideoH26xPacketBuffer flag.

This unlaunches the experiment for H264 due to issues reported for H264

where the old packet buffer behaves better than the new one. A recently

introduced issue will be fixed separately from this CL and rollout

restarted.

This CL is not a clean revert though (see delta with PS#1):

we will continue to use the H26xPacketBuffer for the new codec H265

because it does not work with the old packet buffer anyway.

Bug: webrtc:41480904

Change-Id: Icac49fa70f1c78d1ed596a7838d1417f6588a8b4

Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/380861

Reviewed-by: Evan Shrubsole <eshr@webrtc.org>

Reviewed-by: Jianlin Qiu <jianlin.qiu@intel.com>

如上提交后，之前提到的Issue 41480904也被标记为fixed了，从2021到2025四年的跨度，WebRTC总算完成H265的支持。

根据提交代码可以知道，WebRTC-VideoH26xPacketBuffer特性默认关闭的，接收到视频RTP包时，相关处理如下：

bool RtpVideoStreamReceiver2::OnReceivedPayloadData() {
// 对于H265，默认启用H26xPacketBuffer处理，只有WebRTC-VideoH26xPacketBuffer特性
// 开启，才会使用H26xPacketBuffer处理H264，这是因为对于H264，H26xPacketBuffer
// 处理表现不如旧的PacketBuffer处理
if (h26x_packet_buffer_ && UseH26xPacketBuffer(packet->codec())) {
OnInsertedPacket(h26x_packet_buffer_->InsertPacket(std::move(packet)));
} else {
OnInsertedPacket(packet_buffer_.InsertPacket(std::move(packet)));
}
}
bool RtpVideoStreamReceiver2::UseH26xPacketBuffer(
std::optional<VideoCodecType> codec) const {
if (codec == kVideoCodecH265) {
return true;
}
if (codec == kVideoCodecH264) {
return env_.field_trials().IsEnabled("WebRTC-Video-H26xPacketBuffer");
}
return false;
}