我构建了一个测试驱动程序，用于编码我捕获的一系列图像。我正在使用libx264，并根据这个人的答案基于我的驱动程序：
在我的情况下，我开始通过读取JPG图像并转换为YUV并将相同的帧一遍又一遍地传递给x264编码器。
我的期望是，因为帧是相同的，所以编码器的输出将非常小且恒定。
相反，我发现NAL有效负载从几个字节变化到几KB，并且根据我在编码器参数中指定的帧速率而变化很大。
显然我不懂视频编码。为什么输出大小变化太大？
int main()
{
Image image(WIDTH, HEIGHT);
image.FromJpeg("frame-1.jpg");
unsigned char *data = image.GetRGB();
x264_param_t param;
x264_param_default_preset(¶m, "fast", "zerolatency");
param.i_threads = 1;
param.i_width = WIDTH;
param.i_height = HEIGHT;
param.i_fps_num = FPS;
param.i_fps_den = 1;
// Intra refres:
param.i_keyint_max = FPS;
param.b_intra_refresh = 1;
//Rate control:
param.rc.i_rc_method = X264_RC_CRF;
param.rc.f_rf_constant = FPS-5;
param.rc.f_rf_constant_max = FPS+5;
//For streaming:
param.b_repeat_headers = 1;
param.b_annexb = 1;
x264_param_apply_profile(¶m, "baseline");
// initialize the encoder
x264_t* encoder = x264_encoder_open(¶m);
x264_picture_t pic_in, pic_out;
x264_picture_alloc(&pic_in, X264_CSP_I420, WIDTH, HEIGHT);
// X264 expects YUV420P data use libswscale
// (from ffmpeg) to convert images to the right format
struct SwsContext* convertCtx =
sws_getContext(WIDTH, HEIGHT, PIX_FMT_RGB24, WIDTH, HEIGHT,
PIX_FMT_YUV420P, SWS_FAST_BILINEAR,
NULL, NULL, NULL);
// encoding is as simple as this then, for each frame do:
// data is a pointer to your RGB structure
int srcstride = WIDTH*3; //RGB stride is just 3*width
sws_scale(convertCtx, &data, &srcstride, 0, HEIGHT,
pic_in.img.plane, pic_in.img.i_stride);
x264_nal_t* nals;
int i_nals;
int frame_size =
x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);
int max_loop=15;
int this_loop=1;
while (frame_size >= 0 && --max_loop)
{
cout << "------------" << this_loop++ << "-----------------\n";
cout << "Frame size = " << frame_size << endl;
cout << "output has " << pic_out.img.i_csp << " colorspace\n";
cout << "output has " << pic_out.img.i_plane << " # img planes\n";
cout << "i_nals = " << i_nals << endl;
for (int n=0; n<i_nals; n++)
cout << "nal[" << n << "] payload size = "
<< nals[n].i_payload << endl;
// clean this input frame and grab another
x264_picture_clean(&pic_in);
x264_picture_alloc(&pic_in, X264_CSP_I420, WIDTH, HEIGHT);
sws_scale(convertCtx, &data, &srcstride, 0, HEIGHT,
pic_in.img.plane, pic_in.img.i_stride);
frame_size=
x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);
}
delete [] data;
return 0;
}
我正在阅读的原始JPG图像是320x240，在磁盘上大约是9KB。通过编码器运行相同图像的输出如下所示：
x264 [warning]: ref > 1 + intra-refresh is not supported
x264 [info]: using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.2 AVX
x264 [info]: profile Constrained Baseline, level 1.3
------------1-----------------
Frame size = 17412
output has 3 colorspace
output has 2 # img planes
i_nals = 4
nal[0] payload size = 26
nal[1] payload size = 8
nal[2] payload size = 610
nal[3] payload size = 16768
------------2-----------------
Frame size = 11
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 11
------------3-----------------
Frame size = 11
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 11
------------4-----------------
Frame size = 16
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 16
------------5-----------------
Frame size = 104
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 104
------------6-----------------
Frame size = 973
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 973
------------7-----------------
Frame size = 4576
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 4576
------------8-----------------
Frame size = 4040
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 4040
------------9-----------------
Frame size = 3917
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 3917
------------10-----------------
Frame size = 3799
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 3799
------------11-----------------
Frame size = 2454
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 2454
------------12-----------------
Frame size = 1641
output has 3 colorspace
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 1641
------------13-----------------
Frame size = 1121
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 1121
------------14-----------------
Frame size = 247
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 247
如果我将FPS设置为10而不是30，则输出大小会发生显着变化：
x264 [warning]: ref > 1 + intra-refresh is not supported
x264 [info]: using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.2 AVX
x264 [info]: profile Constrained Baseline, level 1.1
------------1-----------------
Frame size = 60120
output has 3 colorspace
output has 2 # img planes
i_nals = 4
nal[0] payload size = 25
nal[1] payload size = 9
nal[2] payload size = 609
nal[3] payload size = 59477
------------2-----------------
Frame size = 10
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 10
------------3-----------------
Frame size = 151
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 151
------------4-----------------
Frame size = 2329
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 2329
------------5-----------------
Frame size = 1466
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 1466
------------6-----------------
Frame size = 539
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 539
------------7-----------------
Frame size = 311
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 311
------------8-----------------
Frame size = 291
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 291
------------9-----------------
Frame size = 302
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 302
------------10-----------------
Frame size = 287
output has 3 colorspace
output has 2 # img planes
i_nals = 1
nal[0] payload size = 287
------------11-----------------
Frame size = 11937
output has 3 colorspace
output has 2 # img planes
i_nals = 4
nal[0] payload size = 25
nal[1] payload size = 9
nal[2] payload size = 9
nal[3] payload size = 11894
答案 0 :(得分：2)
卸下：
param.b_intra_refresh = 1;
//Rate control:
param.rc.i_rc_method = X264_RC_CRF;
param.rc.f_rf_constant = FPS-5;
param.rc.f_rf_constant_max = FPS+5;
然后添加：
param.rc.i_qp_constant = 18;
param.rc.i_qp_min = 18;
param.rc.i_qp_max = 18;