(原创)基于ZedBoard的Webcam设计(五):x264编码在zedboard上的实现(软编码)

(原创)基于ZedBoard的Webcam设计(四):MJPG编码和AVI封装中,我们在zed上完成了视频的采集和存储,但是MJPG只是对一帧一帧图片进行编码,编码效率只有10%。x264-snapshot提供了开源x264源代码,已经广泛用于嵌入式解决方案中。本小节将介绍zed上x264-snapshot源码的配置,并在zed上使用High版本、main版本对一个33M的测试视频进行编码,测试编码效率。

更多更新请关注我的博客:@超群天晴 http://www.cnblogs.com/surpassal/

 

相关阅读: 

(原创)基于ZedBoard的Webcam设计(一):USB摄像头(V4L2接口)的图片采集  

(原创)基于ZedBoard的Webcam设计(二):USB摄像头图片采集+QT显示  

(原创)基于ZedBoard的Webcam设计(三):视频的采集和动态显示  

(原创)基于ZedBoard的Webcam设计(四):MJPG编码和AVI封装  

(原创)基于ZedBoard的Webcam设计(五):x264编码在zedboard上的实现(软编码)

 

 

硬件平台:Digilent ZedBoard

开发环境:Windows XP 32 bit + Wmare 8.0 + Ubuntu 10.04 +Qt+ arm-linux-xilinx-gnueabi交叉编译环境 

Zedboard linux: Digilent OOB Design  

 

一、x264开源包获取

x264-snapshot提供了开源x264源代码,已经在X86和ARM架构下均已实现。linux下可以使用git获得最新的代码包

git clone git://git.videolan.org/x264.git

也可以通过网页下载:

http://download.videolan.org/pub/videolan/x264/snapshots/

二、配置、安装x264-snapshot

下载到源码后,对其进行配置,以便在后续make时编译出zed上可以运行的可执行程序

1、解压源码包后,进入源码目录

./configure --host=arm-xilinx-linux-gnueabi --prefix=/opt/rcq --enable-shared --disable-asm

congfig之后,设定了host为arm-xilinx-linux-gnueabi,install路径是/opt/rcq

2、修改config.mak文件

针对zed的gcc,需要修改config.mak文件

 1 SRCPATH=.
 2 prefix=/opt/rcq
 3 exec_prefix=${prefix}
 4 bindir=${exec_prefix}/bin
 5 libdir=${exec_prefix}/lib
 6 includedir=${prefix}/include
 7 ARCH=ARM
 8 SYS=LINUX
 9 CC=arm-xilinx-linux-gnueabi-gcc
10 CFLAGS=-Wshadow -O3 -fno-fast-math  -Wall -I. -I$(SRCPATH) -std=gnu99 -fPIC -fomit-frame-pointer -fno-tree-vectorize
11 DEPMM=-MM -g0
12 DEPMT=-MT
13 LD=arm-xilinx-linux-gnueabi-gcc -o 
14 LDFLAGS= -lm -lpthread
15 LIBX264=libx264.a
16 AR=arm-xilinx-linux-gnueabi-ar rc 
17 RANLIB=arm-xilinx-linux-gnueabi-ranlib
18 STRIP=arm-xilinx-linux-gnueabi-strip
19 AS=
20 ASFLAGS= -DHAVE_ALIGNED_STACK=1 -DPIC -DHIGH_BIT_DEPTH=0 -DBIT_DEPTH=8
21 RC=
22 RCFLAGS=
23 EXE=
24 HAVE_GETOPT_LONG=1
25 DEVNULL=/dev/null
26 PROF_GEN_CC=-fprofile-generate
27 PROF_GEN_LD=-fprofile-generate
28 PROF_USE_CC=-fprofile-use
29 PROF_USE_LD=-fprofile-use
30 default: cli
31 install: install-cli
32 SOSUFFIX=so
33 SONAME=libx264.so.129
34 SOFLAGS=-shared -Wl,-soname,$(SONAME)  -Wl,-Bsymbolic
35 default: lib-shared
36 install: install-lib-shared
37 LDFLAGSCLI = 
38 CLI_LIBX264 = $(LIBX264)

其中9、13、16、17、18行为修改后的。

3、make

make install
make

完运行库的安装和成执行文件的生成

三、在zed上测试x264

将可执行x264和测试rcq.yuv文件拷贝到zed上,使用默认运行命令

./x264 rcq.yuv --input-res 640x480 -o rcq.flv

其中--input-res 640x480设定输入yuv视频帧的大小,rcq.flv是输出文件,可以设定为.mkv/.mp4/H264等。从控制台可以看到

使用的profile是最高等级High level 3.0,但是的编码速率只有1.40fps……情何以堪……

编码结束后:

生成的rcq.flv文件大小348k,相比较原来的rcq.yuv文件大小33M,压缩率在1%。

可以使用最快编码方式,命令和参数如下

./x264 rcq.yuv --input-res 640x480 -o rcq.flv --no-8x8dct --aq-mode 0 --b-adapt 0 --bframes 0 --no-cabac --no-deblock --no-mbtree --me dia --no-mixed-refs --partitions none --rc-lookahead 0 --ref 1 --scenecut 0 --subme 0 --trellis 0

编码速率能有22fps,这样还凑合。生成的rcq.flv文件大小787K,压缩率在5%。

四、x264命令和参数(fullhelp)

View Code
Syntax: x264 [options] -o outfile infile

Infile can be raw (in which case resolution is required),
  or YUV4MPEG (*.y4m),
  or Avisynth if compiled with support (no).
  or libav* formats if compiled with lavf support (no) or ffms support (no).
Outfile type is selected by filename:
 .264 -> Raw bytestream
 .mkv -> Matroska
 .flv -> Flash Video
 .mp4 -> MP4 if compiled with GPAC support (no)
Output bit depth: 8 (configured at compile time)

Options:

  -h, --help                  List basic options
      --longhelp              List more options
      --fullhelp              List all options

Example usage:

      Constant quality mode:
            x264 --crf 24 -o <output> <input>

      Two-pass with a bitrate of 1000kbps:
            x264 --pass 1 --bitrate 1000 -o <output> <input>
            x264 --pass 2 --bitrate 1000 -o <output> <input>

      Lossless:
            x264 --qp 0 -o <output> <input>

      Maximum PSNR at the cost of speed and visual quality:
            x264 --preset placebo --tune psnr -o <output> <input>

      Constant bitrate at 1000kbps with a 2 second-buffer:
            x264 --vbv-bufsize 2000 --bitrate 1000 -o <output> <input>

Presets:

      --profile <string>      Force the limits of an H.264 profile
                                  Overrides all settings.
                                  - baseline:
                                    --no-8x8dct --bframes 0 --no-cabac
                                    --cqm flat --weightp 0
                                    No interlaced.
                                    No lossless.
                                  - main:
                                    --no-8x8dct --cqm flat
                                    No lossless.
                                  - high:
                                    No lossless.
                                  - high10:
                                    No lossless.
                                    Support for bit depth 8-10.
                                  - high422:
                                    No lossless.
                                    Support for bit depth 8-10.
                                    Support for 4:2:0/4:2:2 chroma subsampling.
                                  - high444:
                                    Support for bit depth 8-10.
                                    Support for 4:2:0/4:2:2/4:4:4 chroma subsampling.
      --preset <string>       Use a preset to select encoding settings [medium]
                                  Overridden by user settings.
                                  - ultrafast:
                                    --no-8x8dct --aq-mode 0 --b-adapt 0
                                    --bframes 0 --no-cabac --no-deblock
                                    --no-mbtree --me dia --no-mixed-refs
                                    --partitions none --rc-lookahead 0 --ref 1
                                    --scenecut 0 --subme 0 --trellis 0
                                    --no-weightb --weightp 0
                                  - superfast:
                                    --no-mbtree --me dia --no-mixed-refs
                                    --partitions i8x8,i4x4 --rc-lookahead 0
                                    --ref 1 --subme 1 --trellis 0 --weightp 1
                                  - veryfast:
                                    --no-mixed-refs --rc-lookahead 10
                                    --ref 1 --subme 2 --trellis 0 --weightp 1
                                  - faster:
                                    --no-mixed-refs --rc-lookahead 20
                                    --ref 2 --subme 4 --weightp 1
                                  - fast:
                                    --rc-lookahead 30 --ref 2 --subme 6
                                    --weightp 1
                                  - medium:
                                    Default settings apply.
                                  - slow:
                                    --b-adapt 2 --direct auto --me umh
                                    --rc-lookahead 50 --ref 5 --subme 8
                                  - slower:
                                    --b-adapt 2 --direct auto --me umh
                                    --partitions all --rc-lookahead 60
                                    --ref 8 --subme 9 --trellis 2
                                  - veryslow:
                                    --b-adapt 2 --bframes 8 --direct auto
                                    --me umh --merange 24 --partitions all
                                    --ref 16 --subme 10 --trellis 2
                                    --rc-lookahead 60
                                  - placebo:
                                    --bframes 16 --b-adapt 2 --direct auto
                                    --slow-firstpass --no-fast-pskip
                                    --me tesa --merange 24 --partitions all
                                    --rc-lookahead 60 --ref 16 --subme 11
                                    --trellis 2
      --tune <string>         Tune the settings for a particular type of source
                              or situation
                                  Overridden by user settings.
                                  Multiple tunings are separated by commas.
                                  Only one psy tuning can be used at a time.
                                  - film (psy tuning):
                                    --deblock -1:-1 --psy-rd <unset>:0.15
                                  - animation (psy tuning):
                                    --bframes {+2} --deblock 1:1
                                    --psy-rd 0.4:<unset> --aq-strength 0.6
                                    --ref {Double if >1 else 1}
                                  - grain (psy tuning):
                                    --aq-strength 0.5 --no-dct-decimate
                                    --deadzone-inter 6 --deadzone-intra 6
                                    --deblock -2:-2 --ipratio 1.1 
                                    --pbratio 1.1 --psy-rd <unset>:0.25
                                    --qcomp 0.8
                                  - stillimage (psy tuning):
                                    --aq-strength 1.2 --deblock -3:-3
                                    --psy-rd 2.0:0.7
                                  - psnr (psy tuning):
                                    --aq-mode 0 --no-psy
                                  - ssim (psy tuning):
                                    --aq-mode 2 --no-psy
\                                  - fastdecode:
                                    --no-cabac --no-deblock --no-weightb
                                    --weightp 0
                                  - zerolatency:
                                    --bframes 0 --force-cfr --no-mbtree
                                    --sync-lookahead 0 --sliced-threads
                                    --rc-lookahead 0
      --slow-firstpass        Don't force these faster settings with --pass 1:
                                  --no-8x8dct --me dia --partitions none
                                  --ref 1 --subme {2 if >2 else unchanged}
                                  --trellis 0 --fast-pskip

Frame-type options:

  -I, --keyint <integer or "infinite"> Maximum GOP size [250]
  -i, --min-keyint <integer>  Minimum GOP size [auto]
      --no-scenecut           Disable adaptive I-frame decision
      --scenecut <integer>    How aggressively to insert extra I-frames [40]
      --intra-refresh         Use Periodic Intra Refresh instead of IDR frames
  -b, --bframes <integer>     Number of B-frames between I and P [3]
      --b-adapt <integer>     Adaptive B-frame decision method [1]
                                  Higher values may lower threading efficiency.
                                  - 0: Disabled
                                  - 1: Fast
                                  - 2: Optimal (slow with high --bframes)
      --b-bias <integer>      Influences how often B-frames are used [0]
      --b-pyramid <string>    Keep some B-frames as references [normal]
                                  - none: Disabled
                                  - strict: Strictly hierarchical pyramid
                                  - normal: Non-strict (not Blu-ray compatible)
      --open-gop              Use recovery points to close GOPs
                              Only available with b-frames
      --no-cabac              Disable CABAC
  -r, --ref <integer>         Number of reference frames [3]
      --no-deblock            Disable loop filter
  -f, --deblock <alpha:beta>  Loop filter parameters [0:0]
      --slices <integer>      Number of slices per frame; forces rectangular
                              slices and is overridden by other slicing options
      --slice-max-size <integer> Limit the size of each slice in bytes
      --slice-max-mbs <integer> Limit the size of each slice in macroblocks
      --tff                   Enable interlaced mode (top field first)
      --bff                   Enable interlaced mode (bottom field first)
      --constrained-intra     Enable constrained intra prediction.
      --pulldown <string>     Use soft pulldown to change frame rate
                                  - none, 22, 32, 64, double, triple, euro (requires cfr input)
      --fake-interlaced       Flag stream as interlaced but encode progressive.
                              Makes it possible to encode 25p and 30p Blu-Ray
                              streams. Ignored in interlaced mode.
      --frame-packing <integer> For stereoscopic videos define frame arrangement
                                  - 0: checkerboard - pixels are alternatively from L and R
                                  - 1: column alternation - L and R are interlaced by column
                                  - 2: row alternation - L and R are interlaced by row
                                  - 3: side by side - L is on the left, R on the right
                                  - 4: top bottom - L is on top, R on bottom
                                  - 5: frame alternation - one view per frame

Ratecontrol:

  -q, --qp <integer>          Force constant QP (0-69, 0=lossless)
  -B, --bitrate <integer>     Set bitrate (kbit/s)
      --crf <float>           Quality-based VBR (0-51) [23.0]
      --rc-lookahead <integer> Number of frames for frametype lookahead [40]
      --vbv-maxrate <integer> Max local bitrate (kbit/s) [0]
      --vbv-bufsize <integer> Set size of the VBV buffer (kbit) [0]
      --vbv-init <float>      Initial VBV buffer occupancy [0.9]
      --crf-max <float>       With CRF+VBV, limit RF to this value
                                  May cause VBV underflows!
      --qpmin <integer>       Set min QP [0]
      --qpmax <integer>       Set max QP [69]
      --qpstep <integer>      Set max QP step [4]
      --ratetol <float>       Tolerance of ABR ratecontrol and VBV [1.0]
      --ipratio <float>       QP factor between I and P [1.40]
      --pbratio <float>       QP factor between P and B [1.30]
      --chroma-qp-offset <integer>  QP difference between chroma and luma [0]
      --aq-mode <integer>     AQ method [1]
                                  - 0: Disabled
                                  - 1: Variance AQ (complexity mask)
                                  - 2: Auto-variance AQ (experimental)
      --aq-strength <float>   Reduces blocking and blurring in flat and
                              textured areas. [1.0]

  -p, --pass <integer>        Enable multipass ratecontrol
                                  - 1: First pass, creates stats file
                                  - 2: Last pass, does not overwrite stats file
                                  - 3: Nth pass, overwrites stats file
      --stats <string>        Filename for 2 pass stats ["x264_2pass.log"]
      --no-mbtree             Disable mb-tree ratecontrol.
      --qcomp <float>         QP curve compression [0.60]
      --cplxblur <float>      Reduce fluctuations in QP (before curve compression) [20.0]
      --qblur <float>         Reduce fluctuations in QP (after curve compression) [0.5]
      --zones <zone0>/<zone1>/...  Tweak the bitrate of regions of the video
                              Each zone is of the form
                                  <start frame>,<end frame>,<option>
                                  where <option> is either
                                      q=<integer> (force QP)
                                  or  b=<float> (bitrate multiplier)
      --qpfile <string>       Force frametypes and QPs for some or all frames
                              Format of each line: framenumber frametype QP
                              QP is optional (none lets x264 choose). Frametypes: I,i,K,P,B,b.
                                  K=<I or i> depending on open-gop setting
                              QPs are restricted by qpmin/qpmax.

Analysis:

  -A, --partitions <string>   Partitions to consider ["p8x8,b8x8,i8x8,i4x4"]
                                  - p8x8, p4x4, b8x8, i8x8, i4x4
                                  - none, all
                                  (p4x4 requires p8x8. i8x8 requires --8x8dct.)
      --direct <string>       Direct MV prediction mode ["spatial"]
                                  - none, spatial, temporal, auto
      --no-weightb            Disable weighted prediction for B-frames
      --weightp <integer>     Weighted prediction for P-frames [2]
                                  - 0: Disabled
                                  - 1: Weighted refs
                                  - 2: Weighted refs + Duplicates
      --me <string>           Integer pixel motion estimation method ["hex"]
                                  - dia: diamond search, radius 1 (fast)
                                  - hex: hexagonal search, radius 2
                                  - umh: uneven multi-hexagon search
                                  - esa: exhaustive search
                                  - tesa: hadamard exhaustive search (slow)
      --merange <integer>     Maximum motion vector search range [16]
      --mvrange <integer>     Maximum motion vector length [-1 (auto)]
      --mvrange-thread <int>  Minimum buffer between threads [-1 (auto)]
  -m, --subme <integer>       Subpixel motion estimation and mode decision [7]
                                  - 0: fullpel only (not recommended)
                                  - 1: SAD mode decision, one qpel iteration
                                  - 2: SATD mode decision
                                  - 3-5: Progressively more qpel
                                  - 6: RD mode decision for I/P-frames
                                  - 7: RD mode decision for all frames
                                  - 8: RD refinement for I/P-frames
                                  - 9: RD refinement for all frames
                                  - 10: QP-RD - requires trellis=2, aq-mode>0
                                  - 11: Full RD: disable all early terminations
      --psy-rd <float:float>  Strength of psychovisual optimization ["1.0:0.0"]
                                  #1: RD (requires subme>=6)
                                  #2: Trellis (requires trellis, experimental)
      --no-psy                Disable all visual optimizations that worsen
                              both PSNR and SSIM.
      --no-mixed-refs         Don't decide references on a per partition basis
      --no-chroma-me          Ignore chroma in motion estimation
      --no-8x8dct             Disable adaptive spatial transform size
  -t, --trellis <integer>     Trellis RD quantization. [1]
                                  - 0: disabled
                                  - 1: enabled only on the final encode of a MB
                                  - 2: enabled on all mode decisions
      --no-fast-pskip         Disables early SKIP detection on P-frames
      --no-dct-decimate       Disables coefficient thresholding on P-frames
      --nr <integer>          Noise reduction [0]

      --deadzone-inter <int>  Set the size of the inter luma quantization deadzone [21]
      --deadzone-intra <int>  Set the size of the intra luma quantization deadzone [11]
                                  Deadzones should be in the range 0 - 32.
      --cqm <string>          Preset quant matrices ["flat"]
                                  - jvt, flat
      --cqmfile <string>      Read custom quant matrices from a JM-compatible file
                                  Overrides any other --cqm* options.
      --cqm4 <list>           Set all 4x4 quant matrices
                                  Takes a comma-separated list of 16 integers.
      --cqm8 <list>           Set all 8x8 quant matrices
                                  Takes a comma-separated list of 64 integers.
      --cqm4i, --cqm4p, --cqm8i, --cqm8p <list>
                              Set both luma and chroma quant matrices
      --cqm4iy, --cqm4ic, --cqm4py, --cqm4pc <list>
                              Set individual quant matrices

Video Usability Info (Annex E):
The VUI settings are not used by the encoder but are merely suggestions to
the playback equipment. See doc/vui.txt for details. Use at your own risk.

      --overscan <string>     Specify crop overscan setting ["undef"]
                                  - undef, show, crop
      --videoformat <string>  Specify video format ["undef"]
                                  - component, pal, ntsc, secam, mac, undef
      --range <string>        Specify color range ["auto"]
                                  - auto, tv, pc
      --colorprim <string>    Specify color primaries ["undef"]
                                  - undef, bt709, bt470m, bt470bg
                                    smpte170m, smpte240m, film
      --transfer <string>     Specify transfer characteristics ["undef"]
                                  - undef, bt709, bt470m, bt470bg, linear,
                                    log100, log316, smpte170m, smpte240m
      --colormatrix <string>  Specify color matrix setting ["???"]
                                  - undef, bt709, fcc, bt470bg
                                    smpte170m, smpte240m, GBR, YCgCo
      --chromaloc <integer>   Specify chroma sample location (0 to 5) [0]
      --nal-hrd <string>      Signal HRD information (requires vbv-bufsize)
                                  - none, vbr, cbr (cbr not allowed in .mp4)
      --pic-struct            Force pic_struct in Picture Timing SEI
      --crop-rect <string>    Add 'left,top,right,bottom' to the bitstream-level
                              cropping rectangle

Input/Output:

  -o, --output <string>       Specify output file
      --muxer <string>        Specify output container format ["auto"]
                                  - auto, raw, mkv, flv
      --demuxer <string>      Specify input container format ["auto"]
                                  - auto, raw, y4m
      --input-fmt <string>    Specify input file format (requires lavf support)
      --input-csp <string>    Specify input colorspace format for raw input
                              - valid csps for `raw' demuxer:
                                i420, yv12, nv12, i422, yv16, nv16, i444, yv24, bgr, bgra, rgb
      --output-csp <string>   Specify output colorspace ["i420"]
                                  - i420, i422, i444, rgb
      --input-depth <integer> Specify input bit depth for raw input
      --input-range <string>  Specify input color range ["auto"]
                                  - auto, tv, pc
      --input-res <intxint>   Specify input resolution (width x height)
      --index <string>        Filename for input index file
      --sar width:height      Specify Sample Aspect Ratio
      --fps <float|rational>  Specify framerate
      --seek <integer>        First frame to encode
      --frames <integer>      Maximum number of frames to encode
      --level <string>        Specify level (as defined by Annex A)
      --bluray-compat         Enable compatibility hacks for Blu-ray support

  -v, --verbose               Print stats for each frame
      --no-progress           Don't show the progress indicator while encoding
      --quiet                 Quiet Mode
      --log-level <string>    Specify the maximum level of logging ["info"]
                                  - none, error, warning, info, debug
      --psnr                  Enable PSNR computation
      --ssim                  Enable SSIM computation
      --threads <integer>     Force a specific number of threads
      --lookahead-threads <integer> Force a specific number of lookahead threads
      --sliced-threads        Low-latency but lower-efficiency threading
      --thread-input          Run Avisynth in its own thread
      --sync-lookahead <integer> Number of buffer frames for threaded lookahead
      --non-deterministic     Slightly improve quality of SMP, at the cost of repeatability
      --cpu-independent       Ensure exact reproducibility across different cpus,
                                  as opposed to letting them select different algorithms
      --asm <integer>         Override CPU detection
      --no-asm                Disable all CPU optimizations
      --visualize             Show MB types overlayed on the encoded video
      --dump-yuv <string>     Save reconstructed frames
      --sps-id <integer>      Set SPS and PPS id numbers [0]
      --aud                   Use access unit delimiters
      --force-cfr             Force constant framerate timestamp generation
      --tcfile-in <string>    Force timestamp generation with timecode file
      --tcfile-out <string>   Output timecode v2 file from input timestamps
      --timebase <int/int>    Specify timebase numerator and denominator
                 <integer>    Specify timebase numerator for input timecode file
                              or specify timebase denominator for other input
      --dts-compress          Eliminate initial delay with container DTS hack

Filtering:

      --vf, --video-filter <filter0>/<filter1>/... Apply video filtering to the input file

      Filter options may be specified in <filter>:<option>=<value> format.

      Available filters:
      crop:left,top,right,bottom
            removes pixels from the edges of the frame
      select_every:step,offset1[,...]
            apply a selection pattern to input frames
            step: the number of frames in the pattern
            offsets: the offset into the step to select a frame
            see: http://avisynth.org/mediawiki/Select#SelectEvery

五、关于YUV420的格式说明

YUV格式有两大类:planar和packed。
对于planar的YUV格式,先连续存储所有像素点的Y,紧接着存储所有像素点的U,随后是所有像素点的V。
对于packed的YUV格式,每个像素点的Y,U,V是连续交*存储的。

一般的录像程序是先从摄像头得到yuv420 planar的数据,然后编码成h264格式 帧,最后存储成3gp/mpeg等格式的视频文件。

以720×488大小图象YUV420 planar为例,其存储格式是:
共大小为(720×480×3>>1)字节,分为三个部分:Y,U和V
Y分量:    (720×480)个字节  
U(Cb)分量:(720×480>>2)个字节
V(Cr)分量:(720×480>>2)个字节
三个部分内部均是行优先存储,三个部分之间是Y,U,V 顺序存储。
即YUV数据的0--720×480字节是Y分量值,
           720×480--720×480×5/4字节是U分量
           720×480×5/4 --720×480×3/2字节是V分量。

一副w*h的yuv420图像数据的大小为w*h*1.5422 和4:20 转换:

最简单的方式:
YUV4:2:2 ---> YUV4:2:0  Y不变,将U和V信号值在行(垂直方向)在进行一次隔行抽样。
YUV4:2:0 ---> YUV4:2:2  Y不变,将U和V信号值的每一行分别拷贝一份形成连续两行数据。

 六、测试视频

 =====================================================

0、x264-snapshots:http://download.videolan.org/pub/videolan/x264/snapshots/

1、zed可执行文件:x264.rar

2、测试yuv文件:rcq.part1.rar rcq.part2.rar

3、其他通用测试yuv序列:http://www.cipr.rpi.edu/resource/sequences/sif.html

posted on 2013-03-11 22:46  超群天晴  阅读(7151)  评论(3编辑  收藏  举报

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