ios直播技术（2）-- 视频编码

iOS视频编码实践：硬编码与软编码(X264)解析

最新推荐文章于 2023-03-18 14:27:25 发布

w_howell

最新推荐文章于 2023-03-18 14:27:25 发布

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分类专栏：流媒体 ios 直播文章标签：视频直播视频编码 ios硬编码 ios软编码 videotoolbox+x264

本文链接：https://blog.youkuaiyun.com/haowei0926/article/details/56012139

本文介绍了iOS平台上视频编码的技术，重点讲解了从8.0版本开始支持的硬编码及其优势，以及在旧版本系统上使用的X264软编码。内容包括编码器设计、接口创建以及硬编码的实现细节。同时，提到了软编码虽然CPU占用高，但适用于较低版本的iOS系统。

今天给大家分享下视频的编码，由于ios在8.0才支持硬编码，所以这里加入了软编码，openH264和X264均可，这里介绍的是X264。

硬编码由于耗用CPU极低，编码效率高所以优先选择，软编码（X264）占用CPU高，一般在4s上720P 20帧就编不动了吧，当然也有优点，6.X、7.X系统都可用。

首先是编码器的设计图：

H264Encoder作为基类首先是创建编码器接口，当8.0以上系统选择硬编码其他软编码

+ (id)create
{
    if (Version_iOS_8) {
        H264VideoToolboxEncoder *encoder = [[H264VideoToolboxEncoder alloc] init];
        return encoder;
    } else
    {
        H264EncoderImpl *encoder = [[H264EncoderImpl alloc] init];
        return encoder;
    }
    return nil;
}

编码接口，首先检查采集数据的分辨率帧率有无变化，如有变化则去销毁原有的，重新创建编码器，若无则直接编码

- (int)checkEncoder:(struct VideoCapability*)capability
{
    if((*capability)!=(*_usingParam))
    {
        memcpy(_usingParam,capability,sizeof(struct VideoCapability));
        [self finiEncoder];
        if (_pTmpOut)
        {
            free(_pTmpOut);
            _pTmpOut = 0;
        }
        [self initEncoder];
        
        if (!_pTmpCfg)
            _pTmpCfg = (uint8_t*)malloc(100);
        if (!_pTmpOut)
            _pTmpOut = (uint8_t*)malloc(_usingParam->width * _usingParam->height * 2 + 100);
    }
    return 0;
}
- (int)encode:(NativeVideoFrame*)avframe Capability:(struct VideoCapability*)capability
{
    NSAutoLock* autolock = [[NSAutoLock alloc] initWithLock:_lock];
    UNUSED(autolock);
    if (!_running)
        return 0;
    [self checkEncoder:capability];
    
    return [self realEncode:avframe TimeStamp:[Utils now_ms]];
}

H264Encoder的派生类有H264Encoderlmpl(软编)和H264VideoToolboxEncoder(硬编)，他们都实现了基类的三个protected方法。

顺带介绍下OC中protected方法的写法

@interface H264EncoderImpl (Protected)
- (BOOL)initEncoder;
- (void)finiEncoder;
- (int)realEncode:(NativeVideoFrame *)avFrame TimeStamp:(long)ts;
@end

先来介绍下H264Encoderlmpl

//
//  H264EncoderImpl.m
//  AVSession
//
//  Created by whw on 2016/11/22.
//  Copyright © 2016年 meixin. All rights reserved.
//

#import "H264EncoderImpl.h"
#import "x264.h"
#import "AVDefine.h"
#import "libavformat/avformat.h"
#import "Utils.h"
#import "libyuv.h"
#include "VideoDefines.h"
#include "VideoFrame.h"
typedef struct
{
    x264_param_t * param;
    x264_t *handle;
    x264_picture_t * picture;
    x264_nal_t  *nal;
} Encoder;

@interface H264EncoderImpl ()
{
    Encoder*        _encoder;
}

@end
@interface H264EncoderImpl (Protected)
- (BOOL)initEncoder;
- (void)finiEncoder;
- (int)realEncode:(NativeVideoFrame *)avFrame TimeStamp:(long)ts;
@end

@implementation H264EncoderImpl

- (instancetype)init
{
    self = [super init];
    if (self) {
        
    }
    return self;
}
- (int)realEncode:(NativeVideoFrame *)raw TimeStamp:(long)ts
{
    raw->native2i420();
    int framesize = raw->width()*raw->height();
    _encoder->picture->img.i_stride[kYPlane] = raw->stride(kYPlane);
    _encoder->picture->img.i_stride[kUPlane] = raw->stride(kUPlane);
    _encoder->picture->img.i_stride[kVPlane] = raw->stride(kVPlane);
    _encoder->picture->img.i_stride[kNumOfPlanes] = 0;
    memcpy(_encoder->picture->img.plane[kYPlane],raw->buffer(kYPlane), framesize);
    memcpy(_encoder->picture->img.plane[kUPlane],raw->buffer(kUPlane), framesize>>2);
    memcpy(_encoder->picture->img.plane[kVPlane],raw->buffer(kVPlane), framesize>>2);
    _encoder->picture->img.plane[kNumOfPlanes] = 0;
    _encoder->picture->img.i_csp = X264_CSP_I420;
    return [self CompressBuffer:_encoder TS:ts];
}
- (BOOL)initEncoder
{
    Encoder *en = (Encoder *) malloc(sizeof(Encoder));
    en->param = (x264_param_t *) malloc(sizeof(x264_param_t));
    en->picture = (x264_picture_t *) malloc(sizeof(x264_picture_t));
    
    x264_param_default_preset(en->param, "superfast" , "zerolatency");
    
    en->param->b_sliced_threads = 0;
    en->param->i_threads = 1;
    en->param->rc.i_rc_method = X264_RC_ABR;
    
    int realBitrate = [Utils calcBiteRate:_usingParam->width heght:_usingParam->height fps:_usingParam->fps];
    realBitrate = realBitrate>>10;
    en->param->rc.i_vbv_max_bitrate= 2 * realBitrate;
    en->param->rc.i_bitrate = realBitrate;
    en->param->rc.i_vbv_buffer_size = 2 * realBitrate;
    
    en->param->i_fps_num = _usingParam->fps;
    en->param->i_fps_den = 1;
    en->param->i_keyint_min = _usingParam->fps * 2;
    en->param->i_keyint_max = _usingParam->fps * 2;
    
    en->param->i_timebase_num        = 1;
    en->param->i_timebase_den        = 1000;
    
    x264_param_apply_profile(en->param,"baseline");
    
    en->param->i_csp = X264_CSP_I420;
    en->param->i_log_level = X264_LOG_NONE;
    en->param->i_width = _usingParam->width; //set frame width
    en->param->i_height = _usingParam->height; //set frame height

    if ((en->handle = x264_encoder_open(en->param)) == 0) {
        //tyy
        free(en->param);
        free(en->picture);
        free(en);
        return NO;
    }
    /* Create a new pic */
    x264_picture_alloc(en->picture, X264_CSP_I420, en->param->i_width, en->param->i_height);
    
    _encoder = en;
    return YES;
}
- (void)finiEncoder
{
    if(!_encoder)
        return;