视频的封装和编码 ffmpeg视频格式转换

视频的封装和编码
视频格式
1.封装格式 AVI MP4 ASF
2.编码格式 H264 wmv XviD

常用的封装格式

1.AVI 压缩标准可任意选择
2.FLV ts 流媒体格式
3.ASF
4.mp4

常用编码格式
1.视频h264 (AVC Part10),wmv XviD(part2),mjpeg
2.音频acc MP3 ape flac

封装格式和编码格式

----------------------------------------------------------
封装格式(格式头) | 视频编码帧 | 音频编码帧 | 视频编码帧 | 音频编码帧     
----------------------------------------------------------

格式头：mp4(Part14) flv mov avi box音视频信息(编码和格式关键帧索引)

视频编码帧：h264 mpeg-4-10 NAL VCL SPS PPS I B P 解码YUV->转RGB显示

音频编码帧: AAC APE FLAC无损压缩PCM原始音频 解码PCM FLT->转为声卡支持的s16 播放

像素格式

1.BGRA RGBA ARGB32 RGB32 YUV420
2.R = Y + 1.4075 * (V - 128);
3.G = Y - 0.3455 * (U - 128) - 0.7169*(V - 128);
4.B = Y + 1.779 * (U - 128);

PCM音频参数
1.采样率 sample_rate 44100 (CD)
2.通道channels(左右声道)
3.样本大小（格式）sample_simple
-AV_SAMPLE_FMT_S16
-AV_SAMPLE_FMT_FLTP

样本类型planar

1.AV_SAMPLE_FMT_S16 在内存的格式为
c1,c2,c1,c2,c1,c2,…
2.AV_SAMPLE_FMT_S16P 在内存中的格式为:
c1,c1,c1…c2,c2,c2…

H.264/AVC视频编码标准

1.视频编码层面(VCL)
-视频数据的内容
2.网络抽象层面(NAL)
-格式化数据并提供头信息

NAL单元
因此我们平时的每一帧数据就是一个NAL单元(SPS与PPS除外)，在实机的h264数据
帧中，往往帧前面带有00 00 00 01或00 00 01分割符一般来说编码出来的首帧数据为PPS与SPS，接着为I帧

MPEG-4

1.MPEG-4是一套用于音频，视频信息的压缩编码标准
2.MPEG-4 Part 14 MPEG-4 文件格式Part 15 AVC文件格式
3.H264(AVC Part10)

视频转封装示例
1.解封mp4
2.封装为WMV

avformat_open_input
1.AVFormatContext **ps
2.const char *url
3.AVInputFormat *fmt
4.AVDictionary **options	

AVFormatContext

1.封装格式的上下文
2.AVIOContext *pb; //IO上下文
3.AVStream **streams; //视频音频字幕流

AVPacket

int64_t pts; //pts *(num / den)
int64_t dts;
uint8_t *data;int size;
int stream_index;
int flags;

CMakeLists.txt

cmake_minimum_required(VERSION 3.4.1)
project(ffmpeg_pro VERSION 0.1.0 LANGUAGES CXX C)
##配置 预编译库 如ffmpeg库 路径
 
# find_library(AVCODEC_LIBRARY avcodec)
# find_library(AVFORMAT_LIBRARY avformat)
# find_library(AVUTIL_LIBRARY avutil)
# find_library(AVDEVICE_LIBRARY avdevice)
##加入预编译库的头文件 如ffmpeg库 的头文件
#include_directories(include)

add_executable(ffmpeg_pro mp4_to_wmv.cpp)
message(STATUS ${AVCODEC_LIBRARY})

target_link_libraries(
	ffmpeg_pro  
	pthread 
	swresample 
	m 
	swscale 
	avformat	
	avcodec 
	avutil 
	avfilter 
	avdevice 
	postproc 
	z 
	lzma  
	rt)

mp4_to_wmv.cpp

extern "C"
{
	#include 
}
#include 
using namespace std;
int main()
{
	char infile[] = "test.mp4";
	char outfile[] = "test.wmv";	
	//muxer,demuters
	av_register_all();
	AVFormatContext *ic = NULL;

	//open input file
	avformat_open_input(&ic, infile, 0, 0);
	if(!ic)
	{
		cout<<"avformat_open_input failed!"<<endl;
		return -1;
	}
	cout<<"open "<<infile<<" success!"<<endl;

	//2 create output context
	AVFormatContext *oc = NULL;
	avformat_alloc_output_context2(&oc,NULL,NULL,outfile);
	if(!oc)
	{
		cerr<<"avformat_alloc_output_context2 failed"<<outfile;
		return -1;
	}
	///3 add the stream
	AVStream *videoStream = avformat_new_stream(oc,NULL);
	AVStream *audioStream = avformat_new_stream(oc,NULL);

	///4 copy param
	avcodec_parameters_copy(videoStream->codecpar,ic->streams[0]->codecpar);
	avcodec_parameters_copy(audioStream->codecpar,ic->streams[1]->codecpar);

	videoStream->codecpar->codec_tag = 0;
	audioStream->codecpar->codec_tag = 0;

	av_dump_format(ic,0,outfile,0);
	cout<<"==================================="<<endl;
	av_dump_format(oc,0,outfile,1);

	///5 open out file io, write head
	int ret = avio_open(&oc->pb,outfile,AVIO_FLAG_WRITE);
	if(ret < 0)
	{
		cerr<<"avio open failed!"<<endl;
		return -1;
	}

	//
	avformat_write_header(oc,NULL);
	if(ret < 0)
	{
		cerr<<"avformat_write_header failed	!"<<endl;
	}

	AVPacket pkt;

	for(;;)
	{
		int re = av_read_frame(ic, &pkt);
		if(re < 0)
			break;
		pkt.pts = av_rescale_q_rnd(pkt.pts,
			ic->streams[pkt.stream_index]->time_base,
			oc->streams[pkt.stream_index]->time_base,
			(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX)
			);
	
		pkt.dts = av_rescale_q_rnd(pkt.dts,
			ic->streams[pkt.stream_index]->time_base,
			oc->streams[pkt.stream_index]->time_base,
			(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX)
			);
		pkt.pos = -1;
		pkt.duration = av_rescale_q_rnd(pkt.duration,
			ic->streams[pkt.stream_index]->time_base,
			oc->streams[pkt.stream_index]->time_base,
			(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX)
			);
		av_write_frame(oc,&pkt);
		av_packet_unref(&pkt);
		cout<<".";
	}
	av_write_trailer(oc);
	avio_close(oc->pb);
	cout<<"\n============================end========================\n";
	return 0;
}

xz@xiaqiu:~/study/csdn/ffmpeg/mp4_to_wmv/build$ ls
CMakeCache.txt  CMakeFiles  cmake_install.cmake  ffmpeg_pro  Makefile  test.mp4  test.wmv
xz@xiaqiu:~/study/csdn/ffmpeg/mp4_to_wmv/build$ ./ffmpeg_pro 
open test.mp4 success!
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.wmv':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:00:12.58, bitrate: N/A
    Stream #0:0(und): Video: h264 (avc1 / 0x31637661), none, 1294x704, 20 kb/s, SAR 1:1 DAR 647:352, 17.31 fps, 30 tbr, 15360 tbn (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: vorbis (mp4a / 0x6134706D), 48000 Hz, 2 channels, 0 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
===================================
Output #0, asf, to 'test.wmv':
    Stream #0:0: Video: h264, none, 1294x704, q=2-31, 20 kb/s
    Stream #0:1: Audio: vorbis, 48000 Hz, 2 channels, 0 kb/s
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============================end========================
xz@xiaqiu:~/study/csdn/ffmpeg/mp4_to_wmv/build$