decodingencoding文档格式.docx
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Audioencoding\n"
）;
/*findtheMP2encoder编码器？
*/
codec=avcodec_find_encoder（CODEC_ID_MP2）;
//返回0时表明打到了，这个API返回avcodec
if（!
codec）{
fprintf（stderr,"
codecnotfound\n"
exit
（1）;
}
c=avcodec_alloc_context3（codec）;
//储存上下文环境
/*设置参数，都是AVCodecContext的成员变量putsampleparameters*/
c->
bit_rate=64000;
sample_rate=44100;
channels=2;
sample_fmt=AV_SAMPLE_FMT_S16;
/*openit打开流文件*/
if（avcodec_open（c,codec）<
0）{
couldnotopencodec\n"
/*thecodecgivesustheframesize帧尺寸,insamples*/
frame_size=c->
frame_size;
samples=malloc（frame_size*2*c->
channels）;
outbuf_size=10000;
outbuf=malloc（outbuf_size）;
//这些都是自己设置的么？
f=fopen（filename,"
wb"
//文件
f）{
couldnotopen%s\n"
filename）;
/*encodeasingletonesound编码单色声音？
核心代码吧*/
t=0;
//浮点数？
tincr=2*M_PI*440.0/c->
sample_rate;
for（i=0;
i<
200;
i++）{
for（j=0;
j<
j++）{
samples[2*j]=（int）（sin（t）*10000）;
samples[2*j+1]=samples[2*j];
t+=tincr;
/*encodethesamples*/
out_size=avcodec_encode_audio（c,outbuf,outbuf_size,samples）;
fwrite（outbuf,1,out_size,f）;
fclose（f）;
free（outbuf）;
free（samples）;
avcodec_close（c）;
av_free（c）;
}
/**Audiodecoding解码.*/
staticvoidaudio_decode_example（constchar*outfilename,constchar*filename）//解码文件
{
AVCodec*codec;
intlen;
FILE*f,*outfile;
uint8_tinbuf[AUDIO_INBUF_SIZE+FF_INPUT_BUFFER_PADDING_SIZE];
AVPacketavpkt;
AVFrame*decoded_frame=NULL;
av_init_packet（&
avpkt）;
Audiodecoding\n"
/*findthempegaudiodecoder*/
codec=avcodec_find_decoder（CODEC_ID_MP2）;
/*openit*/
rb"
outfile=fopen（outfilename,"
outfile）{
/*decodeuntileof*/
avpkt.data=inbuf;
avpkt.size=fread（inbuf,1,AUDIO_INBUF_SIZE,f）;
while（avpkt.size>
intgot_frame=0;
decoded_frame）{
（decoded_frame=avcodec_alloc_frame（）））{
outofmemory\n"
}else
avcodec_get_frame_defaults（decoded_frame）;
len=avcodec_decode_audio4（c,decoded_frame,&
got_frame,&
if（len<
Errorwhiledecoding\n"
if（got_frame）{
/*ifaframehasbeendecoded,outputit*/
intdata_size=av_samples_get_buffer_size（NULL,c->
channels,
decoded_frame->
nb_samples,
sample_fmt,1）;
fwrite（decoded_frame->
data[0],1,data_size,outfile）;
avpkt.size-=len;
avpkt.data+=len;
avpkt.dts=
avpkt.pts=AV_NOPTS_VALUE;
if（avpkt.size<
AUDIO_REFILL_THRESH）{
/*Refilltheinputbuffer,toavoidtryingtodecode
*incompleteframes.Insteadofthis,onecouldalsouse
*aparser,oruseapropercontainerformatthrough
*libavformat.*/
memmove（inbuf,avpkt.data,avpkt.size）;
len=fread（avpkt.data+avpkt.size,1,
AUDIO_INBUF_SIZE-avpkt.size,f）;
if（len>
0）
avpkt.size+=len;
fclose（outfile）;
av_free（decoded_frame）;
/**Videoencodingexample视频编码*/
staticvoidvideo_encode_example（constchar*filename,intcodec_id）
inti,out_size,size,x,y,outbuf_size;
AVFrame*picture;
Videoencoding\n"
/*findthempeg1videoencoder*/
codec=avcodec_find_encoder（codec_id）;
picture=avcodec_alloc_frame（）;
/*putsampleparameters*/
bit_rate=400000;
/*resolutionmustbeamultipleoftwo*/
width=352;
height=288;
/*framespersecond*/
time_base=（AVRational）{1,25};
gop_size=10;
/*emitoneintraframeeverytenframes*/
max_b_frames=1;
pix_fmt=PIX_FMT_YUV420P;
if（codec_id==CODEC_ID_H264）
av_opt_set（c->
priv_data,"
preset"
"
slow"
0）;
/*allocimageandoutputbuffer*/
outbuf_size=100000;
/*theimagecanbeallocatedbyanymeansandav_image_alloc（）is
*justthemostconvenientwayifav_malloc（）istobeused*/
av_image_alloc（picture->
data,picture->
linesize,
width,c->
height,c->
pix_fmt,1）;
/*encode1secondofvideo*/
25;
fflush（stdout）;
/*prepareadummyimage*/
/*Y*/
for（y=0;
y<
c->
height;
y++）{
for（x=0;
x<
width;
x++）{
picture->
data[0][y*picture->
linesize[0]+x]=x+y+i*3;
/*CbandCr*/
height/2;
width/2;
data[1][y*picture->
linesize[1]+x]=128+y+i*2;
data[2][y*picture->
linesize[2]+x]=64+x+i*5;
/*encodetheimage*/
out_size=avcodec_encode_video（c,outbuf,outbuf_size,picture）;
encodingframe%3d（size=%5d）\n"
i,out_size）;
/*getthedelayedframes*/
for（;
out_size;
i++）{
out_size=avcodec_encode_video（c,outbuf,outbuf_size,NULL）;
writeframe%3d（size=%5d）\n"
/*addsequenceendcodetohavearealmpegfile*/
outbuf[0]=0x00;
outbuf[1]=0x00;
outbuf[2]=0x01;
outbuf[3]=0xb7;
fwrite（outbuf,1,4,f）;
av_free（picture->
data[0]）;
av_free（picture）;
\n"
/**Videodecodingexample*/
staticvoidpgm_save（unsignedchar*buf,intwrap,intxsize,intysize,
char*filename）
inti;
f=fopen（filename,"
w"
fprintf（f,"
P5\n%d%d\n%d\n"
xsize,ysize,255）;
ysize;
i++）
fwrite（buf+i*wrap,1,xsize,f）;
staticvoidvideo_decode_example（constchar*outfilename,constchar*filename）
intframe,got_picture,len;
uint8_tinbuf[INBUF_SIZE+FF_INPUT_BUFFER_PADDING_SIZE];
charbuf[1024];
/*setendofbufferto0（thisensuresthatnooverreadinghappensfordamagedmpegstreams）*/
memset（inbuf+INBUF_SIZE,0,FF_INPUT_BUFFER_PADDING_SIZE）;
Videodecoding\n"
/*findthempeg1videodecoder*/
codec=avcodec_find_decoder（CODEC_ID_MPEG1VIDEO）;
if（codec->
capabilities&
CODEC_CAP_TRUNCATED）
flags|=CODEC_FLAG_TRUNCATED;
/*wedonotsendcompleteframes*/
/*Forsomecodecs,suchasmsmpeg4andmpeg4,widthandheight
MUSTbeinitializedtherebecausethisinformationisnot
availableinthebitstream.*/
/*thecodecgivesustheframesize,insamples*/
frame=0;
;
）{
avpkt.size=fread（inbuf,1,INBUF_SIZE,f）;
if（avpkt.size==0）
break;
/*NOTE1:
somecodecsarestreambased（mpegvideo,mpegaudio）
andthisistheonlymethodtousethembecauseyoucannot
knowthecompresseddatasizebeforeanalysingit.
BUTsomeothercodecs（msmpeg4,mpeg4）areinherentlyframe
based,soyoumustcallthemwithallthedataforone
frameexactly.Youmustalsoinitialize'
width'
and
'
height'
beforeinitializingthem.*/
/*NOTE2:
somecodecsallowtherawparameters（framesize,
samplerate）tobechangedatanyframe.Wehandlethis,so
youshouldalsotakecareofit*/
/*here,weuseastreambaseddecoder（mpeg1video）,sowe
feeddecoderandseeifitcoulddecodeaframe*/
len=avcodec_decode_video2（c,picture,&
got_picture,&
Errorwhiledecodingframe%d\n"
frame）;
if（got_picture）{
savingframe%3d\n"
/*thepictureisallocatedbythedecoder.noneedto
freeit*/
snprintf（buf,sizeof（buf）,outfilename,frame）;
pgm_save（picture->
data[0],picture->
linesize[0],
height,buf）;
frame++;
/*somecodecs,suchasMPEG,transmittheIandPframewitha
latencyofoneframe.Youmustdothefollowingtohavea
chancetogetthelastframeofthevi
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