跨平台xamarin.Android 开发之 ：适配架构(X86_64 、arm64-v8a、 armeabi-v7a )FFmpeg 编码

此代码的编写花费了脑细胞：在每次编码开启编码器到只需要一次编码器的开启优化

前提：编译好FFMpeg 的各平台的动态库

基本上Android X86_64 、 X86、arm64-v8a、 armeabi-v7a 采用FFmpeg 编码的方式基本一直。差异是内存分配和取指有所不同，如果分配不对，直接闪退。

先看看通用的编码，包括编码器创建、编码、释放编码器。

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Drawing;

namespace FFmpegAnalyzer
{
    /// <summary>
    /// 编码器
    /// </summary>
    internal unsafe class FFmpegEncoder
    {
        /// <param name="srcFrameSize">编码前一帧原始数据的大小</param>
        /// <param name="isRgb">rgb数据</param>
        /// <param name="detFrameSize">编码后一帧目标数据的大小</param>
        public FFmpegEncoder(Size srcFrameSize, bool isRgb , Size detFrameSize )
        {
            _srcFrameSize = srcFrameSize;
            _isRgb = isRgb;
            _detFrameSize = detFrameSize == default ? _srcFrameSize : detFrameSize;
            _detFrameSize.Width = (_detFrameSize.Width % 2 == 0) ? _detFrameSize.Width : _detFrameSize.Width - 1;
            _detFrameSize.Height = (_detFrameSize.Height % 2 == 0) ? _detFrameSize.Height : _detFrameSize.Height - 1;
        }

        /// <summary>
        /// 创建编码器
        /// </summary>
        public  void CreateEncoder(AVCodecID codecFormat)
        {
            var originPixelFormat = _isRgb ? AVPixelFormat.AV_PIX_FMT_RGB24 : AVPixelFormat.AV_PIX_FMT_BGRA;
            var destinationPixelFormat = AVPixelFormat.AV_PIX_FMT_YUV420P;
            _pCodec = FFmpeg.avcodec_find_encoder(codecFormat);

            if (_pCodec == null)
                throw new InvalidOperationException("Codec not found.");
            _pCodecContext = FFmpeg.avcodec_alloc_context3(_pCodec);
            _pCodecContext->width = _detFrameSize.Width;
            _pCodecContext->height = _detFrameSize.Height;

            _pCodecContext->framerate = new AVRational { num = 30, den = 1 };
            _pCodecContext->time_base = new AVRational {num = 1, den = 30};
            _pCodecContext->gop_size = 30;
            _pCodecContext->pix_fmt = destinationPixelFormat;
            // 设置预测算法
            _pCodecContext->flags |= FFmpeg.AV_CODEC_FLAG_PSNR;
            _pCodecContext->flags2 |= FFmpeg.AV_CODEC_FLAG2_FAST;
            _pCodecContext->max_b_frames = 0;

            FFmpeg.av_opt_set(_pCodecContext->priv_data, "preset", "veryfast", 0);
            FFmpeg.av_opt_set(_pCodecContext->priv_data, "tune", "zerolatency", 0);

            //打开编码器
            FFmpeg.avcodec_open2(_pCodecContext, _pCodec, null).ThrowExceptionIfError();
            _pConvertContext = FFmpeg.sws_getContext(_srcFrameSize.Width, _srcFrameSize.Height, originPixelFormat, _detFrameSize.Width, _detFrameSize.Height, destinationPixelFormat,
            FFmpeg.SWS_BICUBIC, null, null, null);
            if (_pConvertContext == null)
                throw new ApplicationException("Could not initialize the conversion context.");

            var convertedFrameBufferSize = FFmpeg.av_image_get_buffer_size(destinationPixelFormat, _detFrameSize.Width, _detFrameSize.Height, 1);
            _convertedFrameBufferPtr = Marshal.AllocHGlobal(convertedFrameBufferSize);
            _dstData = new BytePtr4();
            _dstLineSize = new Int4();

            FFmpeg.av_image_fill_arrays(ref _dstData, ref _dstLineSize, (byte*)_convertedFrameBufferPtr, destinationPixelFormat, _detFrameSize.Width, _detFrameSize.Height, 1);
            _isCodecRunning = true;
        }

        /// <summary>
        /// 释放
        /// </summary>
        public  void Dispose()
        {
            if (!_isCodecRunning) return;
            _isCodecRunning = false;
            //释放编码器
            FFmpeg.avcodec_close(_pCodecContext);
            FFmpeg.av_free(_pCodecContext);
            //释放转换器
            Marshal.FreeHGlobal(_convertedFrameBufferPtr);
            FFmpeg.sws_freeContext(_pConvertContext);
        }

        private AVFrame waitToYuvFrame;
        /// <summary>
        /// 编码
        /// </summary>
        /// <param name="frameBytes"></param>
        /// <returns></returns>
        public  byte[] EncodeFrames(byte[] frameBytes)
        {
            if (!_isCodecRunning)
            {
                 throw new InvalidOperationException("编码器未运行!");
            }

            //行跨度：涉及图像内存取值
            var rowPitch = _isRgb ? _srcFrameSize.Width * 3 : _srcFrameSize.Width * 4;
            fixed (byte* pBitmapData = frameBytes)
            {
                waitToYuvFrame = new AVFrame
                {
                    data = new BytePtr8 { [0] = pBitmapData },
                    linesize = new Int8 { [0] = rowPitch },
                    height = _srcFrameSize.Height
                };
                var rgbToYuv = ConvertToYuv(waitToYuvFrame, _detFrameSize);
                byte[] buffer;
                var pPacket = FFmpeg.av_packet_alloc();
                try
                {
                    int error;
                    do
                    {
                        FFmpeg.avcodec_send_frame(_pCodecContext, &rgbToYuv).ThrowExceptionIfError();
                        error = FFmpeg.avcodec_receive_packet(_pCodecContext, pPacket);
                    } while (error == FFmpeg.AVERROR(FFmpeg.EAGAIN));
                    error.ThrowExceptionIfError();
                    buffer = new byte[pPacket->size];
                    Marshal.Copy(new IntPtr(pPacket->data), buffer, 0, pPacket->size);
                }
                finally
                {
                    FFmpeg.av_frame_unref(&rgbToYuv);
                    FFmpeg.av_packet_unref(pPacket);
                }

                return buffer;
            }
        }

        /// <summary>
        /// 转换成Yuv格式
        /// </summary>
        /// <param name="waitConvertYuvFrame"></param>
        /// <param name="detSize">变化后目标大小</param>
        /// <returns></returns>
        private AVFrame ConvertToYuv(AVFrame waitConvertYuvFrame,Size detSize)
        {
            FFmpeg.sws_scale(_pConvertContext, waitConvertYuvFrame.data, waitConvertYuvFrame.linesize, 0, waitConvertYuvFrame.height, _dstData, _dstLineSize);
            var data = new BytePtr8();
            data.UpdateFrom(_dstData);
            var lineSize = new Int8();
            lineSize.UpdateFrom(_dstLineSize);
            IntPtr address = (IntPtr)(&waitConvertYuvFrame);
            Debug.WriteLine("Address: 0x" + address.ToString("X"));
            Debug.WriteLine("Size: " + sizeof(AVFrame));
            FFmpeg.av_frame_unref(waitConvertYuvFrame);  
            return new AVFrame
            {
                data = data,
                linesize = lineSize,
                width = detSize.Width,
                height = detSize.Height
            };
        }

        //编码器
        private AVCodec* _pCodec;
        private AVCodecContext* _pCodecContext;
        //转换缓存区
        private IntPtr _convertedFrameBufferPtr;
        private BytePtr4 _dstData;
        private Int4 _dstLineSize;
        //格式转换
        private SwsContext* _pConvertContext;

        //源数据大小
        private Size _srcFrameSize;
        //源数据大小
        private Size _detFrameSize;

        //三通道
        private readonly bool _isRgb;

        //编码器正在运行
        private bool _isCodecRunning;
    }
}

上面的编码器使用，在Windows 和Andriod X86_64 armeabi-v7a 平台架构上们都可以正常使用。

但是在arm64-v8a 使用使用是，只要使用  &取指。例如：

1 FFmpeg.av_frame_unref(&waitConvertYuvFrame);

2 FFmpeg.avcodec_send_frame(_pCodecContext, &rgbToYuv) 

直接闪退。通过打开FFmpeg 的日志工具 提示内存段错误。既然异常知道了就可以针对处理了，发现是在arm64-v8a主要主动分配内存，那就好修改了，修改的整体代码如下

  AVFrame* pFrame = FFmpeg.av_frame_alloc(); //兼容ARM 64位(arm64-v8a)
                pFrame->data = new BytePtr8 {[0] = pBitmapData};
                pFrame->linesize = new Int8 { [0] = rowPitch };
                pFrame->height = _srcFrameSize.Height;

通过主动申请非托管内存替代托管内存。整体代码如下

using System;
using System.Drawing;
using System.Runtime.InteropServices;

namespace FFmpegAnalyzer
{
    /// <summary>
    /// 编码器
    /// </summary>
    internal unsafe class FFmpegEncoder
    {
        /// <param name="srcFrameSize">编码前一帧原始数据的大小</param>
        /// <param name="isRgb">rgb数据</param>
        /// <param name="detFrameSize">编码后一帧目标数据的大小</param>
        public FFmpegEncoder(Size srcFrameSize, bool isRgb , Size detFrameSize )
        {
            _srcFrameSize = srcFrameSize;
            _isRgb = isRgb;
            _detFrameSize = detFrameSize == default ? _srcFrameSize : detFrameSize;
            _detFrameSize.Width = (_detFrameSize.Width % 2 == 0) ? _detFrameSize.Width : _detFrameSize.Width - 1;
            _detFrameSize.Height = (_detFrameSize.Height % 2 == 0) ? _detFrameSize.Height : _detFrameSize.Height - 1;
        }

        /// <summary>
        /// 创建编码器
        /// </summary>
        public  void CreateEncoder(AVCodecID codecFormat)
        {
            var originPixelFormat = _isRgb ? AVPixelFormat.AV_PIX_FMT_RGB24 : AVPixelFormat.AV_PIX_FMT_BGRA;
            var destinationPixelFormat = AVPixelFormat.AV_PIX_FMT_YUV420P;
            _pCodec = FFmpeg.avcodec_find_encoder(codecFormat);

            if (_pCodec == null)
                throw new InvalidOperationException("Codec not found.");
            _pCodecContext = FFmpeg.avcodec_alloc_context3(_pCodec);
            _pCodecContext->width = _detFrameSize.Width;
            _pCodecContext->height = _detFrameSize.Height;

            _pCodecContext->framerate = new AVRational { num = 30, den = 1 };
            _pCodecContext->time_base = new AVRational {num = 1, den = 30};
            _pCodecContext->gop_size = 30;
            _pCodecContext->pix_fmt = destinationPixelFormat;
            // 设置预测算法
            _pCodecContext->flags |= FFmpeg.AV_CODEC_FLAG_PSNR;
            _pCodecContext->flags2 |= FFmpeg.AV_CODEC_FLAG2_FAST;
            _pCodecContext->max_b_frames = 0;

            FFmpeg.av_opt_set(_pCodecContext->priv_data, "preset", "veryfast", 0);
            FFmpeg.av_opt_set(_pCodecContext->priv_data, "tune", "zerolatency", 0);

            //打开编码器
            FFmpeg.avcodec_open2(_pCodecContext, _pCodec, null).ThrowExceptionIfError();
            _pConvertContext = FFmpeg.sws_getContext(_srcFrameSize.Width, _srcFrameSize.Height, originPixelFormat, _detFrameSize.Width, _detFrameSize.Height, destinationPixelFormat,
            FFmpeg.SWS_BICUBIC, null, null, null);
            if (_pConvertContext == null)
                throw new ApplicationException("Could not initialize the conversion context.");

            var convertedFrameBufferSize = FFmpeg.av_image_get_buffer_size(destinationPixelFormat, _detFrameSize.Width, _detFrameSize.Height, 1);
            _convertedFrameBufferPtr = Marshal.AllocHGlobal(convertedFrameBufferSize);
            _dstData = new BytePtr4();
            _dstLineSize = new Int4();

            FFmpeg.av_image_fill_arrays(ref _dstData, ref _dstLineSize, (byte*)_convertedFrameBufferPtr, destinationPixelFormat, _detFrameSize.Width, _detFrameSize.Height, 1);
            _isCodecRunning = true;
        }

        /// <summary>
        /// 释放
        /// </summary>
        public  void Dispose()
        {
            if (!_isCodecRunning) return;
            _isCodecRunning = false;
            //释放编码器
            FFmpeg.avcodec_close(_pCodecContext);
            FFmpeg.av_free(_pCodecContext);
            //释放转换器
            Marshal.FreeHGlobal(_convertedFrameBufferPtr);
            FFmpeg.sws_freeContext(_pConvertContext);
        }

        /// <summary>
        /// 编码
        /// </summary>
        /// <param name="frameBytes"></param>
        /// <returns></returns>
        public  byte[] EncodeFrames(byte[] frameBytes)
        {
            if (!_isCodecRunning)
            {
                 throw new InvalidOperationException("编码器未运行!");
            }

            //行跨度：涉及图像内存取值
            var rowPitch = _isRgb ? _srcFrameSize.Width * 3 : _srcFrameSize.Width * 4;
            fixed (byte* pBitmapData = frameBytes)
            {
                AVFrame* pFrame = FFmpeg.av_frame_alloc(); 
                pFrame->data = new BytePtr8 {[0] = pBitmapData};
                pFrame->linesize = new Int8 { [0] = rowPitch };
                pFrame->height = _srcFrameSize.Height;
                var rgbToYuv = ConvertToYuv(pFrame, _detFrameSize);
                byte[] buffer;
                var pPacket = FFmpeg.av_packet_alloc();
                try
                {
                    int error;
                    do
                    {
                        FFmpeg.avcodec_send_frame(_pCodecContext, rgbToYuv).ThrowExceptionIfError();
                        error = FFmpeg.avcodec_receive_packet(_pCodecContext, pPacket);
                    } while (error == FFmpeg.AVERROR(FFmpeg.EAGAIN));
                    error.ThrowExceptionIfError();
                    buffer = new byte[pPacket->size];
                    Marshal.Copy(new IntPtr(pPacket->data), buffer, 0, pPacket->size);
                }
                finally
                {
                    FFmpeg.av_frame_unref(rgbToYuv);
                    FFmpeg.av_packet_unref(pPacket);
                }

                return buffer;
            }
        }

        /// <summary>
        /// 转换成Yuv格式
        /// </summary>
        /// <param name="waitConvertYuvFrame"></param>
        /// <param name="detSize">变化后目标大小</param>
        /// <returns></returns>
        private AVFrame* ConvertToYuv(AVFrame* waitConvertYuvFrame,Size detSize)
        {
            FFmpeg.sws_scale(_pConvertContext, waitConvertYuvFrame->data, waitConvertYuvFrame->linesize, 0, waitConvertYuvFrame->height, _dstData, _dstLineSize);
            var data = new BytePtr8();
            data.UpdateFrom(_dstData);
            var lineSize = new Int8();
            lineSize.UpdateFrom(_dstLineSize);
            FFmpeg.av_frame_unref(waitConvertYuvFrame);
            AVFrame* pFrame = FFmpeg.av_frame_alloc();
            pFrame->data = data;
            pFrame->linesize = lineSize;
            pFrame->width = detSize.Width;
            pFrame->height = detSize.Height;
            pFrame->format = (int) AVPixelFormat.AV_PIX_FMT_YUV420P;
            return pFrame;
        }

        //编码器
        private AVCodec* _pCodec;
        private AVCodecContext* _pCodecContext;
        //转换缓存区
        private IntPtr _convertedFrameBufferPtr;
        private BytePtr4 _dstData;
        private Int4 _dstLineSize;
        //格式转换
        private SwsContext* _pConvertContext;

        //源数据大小
        private Size _srcFrameSize;
        //源数据大小
        private Size _detFrameSize;

        //三通道
        private readonly bool _isRgb;

        //编码器正在运行
        private bool _isCodecRunning;
    }
}