0 什么是ffmpeg?
Libav（舊稱：FFmpeg）是一個自由軟件，可以運行音頻和視頻多種格式的錄影、轉檔、流功能[1]，包含了libavcodec ─這是一個用于多個專案中音頻和視頻的解碼器庫，以及 libavformat ——一個音頻與視頻格式轉換庫。
libav的舊稱"FFmpeg"這個單詞中的 "FF" 指的是 "Fast Forward"[2]。有些新手寫信給"FFmpeg"的項目負責人，詢問FF是不是代表“Fast Free”或者“Fast Fourier”等意思，"FFmpeg"的項目負責人回信說“Just for the record, the original meaning of "FF" in FFmpeg is "Fast Forward"...”
http://zh.wikipedia.org/wiki/Libav
?
?一 下載ffmpeg
官方網站： ????http://ffmpeg.zeranoe.com/
訪問???????????????http://ffmpeg.zeranoe.com/builds/
下載ffmpeg windows下發布版
FFmpeg git-f514695 32-bit Shared (Latest)?
?
二?在命令行下學會ffmpeg使用
cd 進入ffmpeg解壓縮目錄下的bin目錄
ffmpeg.exe -i D:/source.avi -vcodec copy -y -r 25 -ss 8 -t 971 D:/demo.mp4? >> D:\clip_info.txt 2>&1
?
這里-vcodec copy參數一定要加，這樣裁剪的時候不會改變視頻的編碼方式，裁剪非常快。
?
ffmpeg主要參數一覽
Hyper fast Audio and Video encoder
usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...
Main options:
-L????????????????? show license
-h????????????????? show help
-?????????????????? show help
-help?????????????? show help
--help????????????? show help
-version??????????? show version
-formats??????????? show available formats
-codecs???????????? show available codecs
-bsfs?????????????? show available bit stream filters
-protocols????????? show available protocols
-filters??????????? show available filters
-pix_fmts?????????? show available pixel formats
-sample_fmts??????? show available audio sample formats
-loglevel loglevel? set libav* logging level
-v loglevel???????? set libav* logging level
-debug flags??????? set debug flags
-report???????????? generate a report
-max_alloc bytes??? set maximum size of a single allocated block
-f fmt????????????? force format
-i filename???????? input file name
-y????????????????? overwrite output files
-n????????????????? do not overwrite output files
-c codec??????????? codec name
-codec codec??????? codec name
-pre preset???????? preset name
-map_metadata outfile[,metadata]:infile[,metadata]? set metadata information of outfile from infile
-t duration???????? record or transcode "duration" seconds of audio/video
-fs limit_size????? set the limit file size in bytes
-ss time_off??????? set the start time offset
-itsoffset time_off? set the input ts offset
-itsscale scale???? set the input ts scale
-timestamp time???? set the recording timestamp ('now' to set the current time)
-metadata string=string? add metadata
-dframes number???? set the number of data frames to record
-timelimit limit??? set max runtime in seconds
-target type??????? specify target file type ("vcd", "svcd", "dvd", "dv", "dv50", "pal-vcd", "ntsc-svcd", ...)
-xerror???????????? exit on error
-frames number????? set the number of frames to record
-tag fourcc/tag???? force codec tag/fourcc
-filter filter_list? set stream filterchain
-stats????????????? print progress report during encoding
-attach filename??? add an attachment to the output file
-dump_attachment filename? extract an attachment into a file
-bsf bitstream_filters? A comma-separated list of bitstream filters
-dcodec codec?????? force data codec ('copy' to copy stream)
Advanced options:
-map [-]input_file_id[:stream_specifier][,sync_file_id[:stream_s? set input stream mapping
-map_channel file.stream.channel[:syncfile.syncstream]? map an audio channel from one stream to another
-map_chapters input_file_index? set chapters mapping
-benchmark????????? add timings for benchmarking
-dump?????????????? dump each input packet
-hex??????????????? when dumping packets, also dump the payload
-re???????????????? read input at native frame rate
-loop_input???????? deprecated, use -loop
-loop_output??????? deprecated, use -loop
-vsync????????????? video sync method
-async????????????? audio sync method
-adrift_threshold threshold? audio drift threshold
-copyts???????????? copy timestamps
-copytb source????? copy input stream time base when stream copying
-shortest?????????? finish encoding within shortest input
-dts_delta_threshold threshold? timestamp discontinuity delta threshold
-copyinkf?????????? copy initial non-keyframes
-q q??????????????? use fixed quality scale (VBR)
-qscale q?????????? use fixed quality scale (VBR)
-streamid streamIndex:value? set the value of an outfile streamid
-muxdelay seconds?? set the maximum demux-decode delay
-muxpreload seconds? set the initial demux-decode delay
-fpre filename????? set options from indicated preset file
Video options:
-vframes number???? set the number of video frames to record
-r rate???????????? set frame rate (Hz value, fraction or abbreviation)
-s size???????????? set frame size (WxH or abbreviation)
-aspect aspect????? set aspect ratio (4:3, 16:9 or 1.3333, 1.7777)
-bits_per_raw_sample number? set the number of bits per raw sample
-croptop size?????? Removed, use the crop filter instead
-cropbottom size??? Removed, use the crop filter instead
-cropleft size????? Removed, use the crop filter instead
-cropright size???? Removed, use the crop filter instead
-padtop size??????? Removed, use the pad filter instead
-padbottom size???? Removed, use the pad filter instead
-padleft size?????? Removed, use the pad filter instead
-padright size????? Removed, use the pad filter instead
-padcolor color???? Removed, use the pad filter instead
-vn???????????????? disable video
-vcodec codec?????? force video codec ('copy' to copy stream)
-sameq????????????? use same quantizer as source (implies VBR)
-same_quant???????? use same quantizer as source (implies VBR)
-pass n???????????? select the pass number (1 or 2)
-passlogfile prefix? select two pass log file name prefix
-vf filter list???? video filters
-b bitrate????????? video bitrate (please use -b:v)
-dn???????????????? disable data
?
三 利用QT4做個簡單圖形界面工具
?
?
這里主要用了QProcess這個類，可以調用外部程序。
關鍵代碼：?
?
??? QString program = "D:\\maxview_video_demo\\ffmpeg\\ffmpeg-git-985e768-win64-static\\bin\\ffmpeg.exe";
??? QString inputPath = ui->videopathLineEdit->text();
??? QFile sourceFile(inputPath);
??? if(!sourceFile.exists()){
??????? QMessageBox::information(this,QString::fromUtf8("提示"),QString::fromUtf8("找不到源文件"));
??????? return;
??? }
??? QString outputPath = QFileInfo(sourceFile).absolutePath() +"/clip.mp4";
??? QFile destFile(outputPath);
??? if(destFile.exists()){
??????? destFile.remove();
??? }
??? QString startTime = ui->videoStartTimeEdit->time().toString("hh:mm:ss");
??? QString len= ui->videoLengthTimeEdit->time().toString("hh:mm:ss");
??? QStringList arguments;
??? arguments << "-i" << inputPath << "-r" << "25"<<"-ss";
??? arguments <<startTime<< "-t" <<?len<< outputPath;
??? QProcess *clipProcess = new QProcess(this);
??? connect(clipProcess,SIGNAL(finished(int)),this,SLOT(clipVideoFinished(int)));
??? clipProcess->start(program, arguments);
?
當視頻截取完成后，進程會發生信號finished(int)，并被QProcess捕捉到，這樣可以調用
clipVideoFinished函數來通知程序視頻裁剪完成了。
)
