【发布时间】：2018-02-12 14:14:42
【问题描述】：
我正在尝试使用 C++ 在 Unreal Engine 4 中对视频进行编码。我可以访问单独的框架。下面是读取viewport's显示像素并存储在缓冲区中的代码。
//Safely get render target resource.
FRenderTarget* RenderTarget = TextureRenderTarget->GameThread_GetRenderTargetResource();
FIntPoint Size = RenderTarget->GetSizeXY();
auto ImageBytes = Size.X* Size.Y * static_cast<int32>(sizeof(FColor));
TArray<uint8> RawData;
RawData.AddUninitialized(ImageBytes);
//Get image raw data.
if (!RenderTarget->ReadPixelsPtr((FColor*)RawData.GetData()))
{
RawData.Empty();
UE_LOG(ExportRenderTargetBPFLibrary, Error, TEXT("ExportRenderTargetAsImage: Failed to get raw data."));
return false;
}
Buffer::getInstance().add(RawData);
虚幻引擎有IImageWrapperModule，您可以使用它从帧中获取图像，但要注意视频编码。我想要的是为实时流媒体服务实时编码帧。
我发现这篇帖子 Encoding a screenshot into a video using FFMPEG 正是我想要的，但我在为我的案例调整这个解决方案时遇到了问题。代码已过时（例如 avcodec_encode_video 更改为 avcodec_encode_video2 具有不同的参数）。
下面是编码器的代码。
void Compressor::DoWork()
{
AVCodec* codec;
AVCodecContext* c = NULL;
//uint8_t* outbuf;
//int /*i, out_size,*/ outbuf_size;
UE_LOG(LogTemp, Warning, TEXT("encoding"));
codec = avcodec_find_encoder(AV_CODEC_ID_MPEG1VIDEO); // finding the H264 encoder
if (!codec) {
UE_LOG(LogTemp, Warning, TEXT("codec not found"));
exit(1);
}
else UE_LOG(LogTemp, Warning, TEXT("codec found"));
c = avcodec_alloc_context3(codec);
c->bit_rate = 400000;
c->width = 1280; // resolution must be a multiple of two (1280x720),(1900x1080),(720x480)
c->height = 720;
c->time_base.num = 1; // framerate numerator
c->time_base.den = 25; // framerate denominator
c->gop_size = 10; // emit one intra frame every ten frames
c->max_b_frames = 1; // maximum number of b-frames between non b-frames
c->keyint_min = 1; // minimum GOP size
c->i_quant_factor = (float)0.71; // qscale factor between P and I frames
//c->b_frame_strategy = 20; ///// find out exactly what this does
c->qcompress = (float)0.6; ///// find out exactly what this does
c->qmin = 20; // minimum quantizer
c->qmax = 51; // maximum quantizer
c->max_qdiff = 4; // maximum quantizer difference between frames
c->refs = 4; // number of reference frames
c->trellis = 1; // trellis RD Quantization
c->pix_fmt = AV_PIX_FMT_YUV420P; // universal pixel format for video encoding
c->codec_id = AV_CODEC_ID_MPEG1VIDEO;
c->codec_type = AVMEDIA_TYPE_VIDEO;
if (avcodec_open2(c, codec, NULL) < 0) {
UE_LOG(LogTemp, Warning, TEXT("could not open codec")); // opening the codec
//exit(1);
}
else UE_LOG(LogTemp, Warning, TEXT("codec oppened"));
FString FinalFilename = FString("C:/Screen/sample.mpg");
auto &PlatformFile = FPlatformFileManager::Get().GetPlatformFile();
auto FileHandle = PlatformFile.OpenWrite(*FinalFilename, true);
if (FileHandle)
{
delete FileHandle; // remove when ready
UE_LOG(LogTemp, Warning, TEXT("file opened"));
while (true)
{
UE_LOG(LogTemp, Warning, TEXT("removing from buffer"));
int nbytes = avpicture_get_size(AV_PIX_FMT_YUV420P, c->width, c->height); // allocating outbuffer
uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes * sizeof(uint8_t));
AVFrame* inpic = av_frame_alloc();
AVFrame* outpic = av_frame_alloc();
outpic->pts = (int64_t)((float)1 * (1000.0 / ((float)(c->time_base.den))) * 90); // setting frame pts
avpicture_fill((AVPicture*)inpic, (uint8_t*)Buffer::getInstance().remove().GetData(),
AV_PIX_FMT_PAL8, c->width, c->height); // fill image with input screenshot
avpicture_fill((AVPicture*)outpic, outbuffer, AV_PIX_FMT_YUV420P, c->width, c->height); // clear output picture for buffer copy
av_image_alloc(outpic->data, outpic->linesize, c->width, c->height, c->pix_fmt, 1);
/*
inpic->data[0] += inpic->linesize[0]*(screenHeight-1);
// flipping frame
inpic->linesize[0] = -inpic->linesize[0];
// flipping frame
struct SwsContext* fooContext = sws_getContext(screenWidth, screenHeight, PIX_FMT_RGB32, c->width, c->height, PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);
sws_scale(fooContext, inpic->data, inpic->linesize, 0, c->height, outpic->data, outpic->linesize); // converting frame size and format
out_size = avcodec_encode_video(c, outbuf, outbuf_size, outpic);
// save in file
*/
}
delete FileHandle;
}
else
{
UE_LOG(LogTemp, Warning, TEXT("Can't open file"));
}
}
有人可以解释 flipping frame 部分（为什么这样做？）以及如何使用avcodec_encode_video2 函数而不是avcodec_encode_video？
【问题讨论】：
标签： c++ ffmpeg video-encoding unreal-engine4