ffmpeg学习9 中级开发阶段
1、课程安排
- H264的解码
- H264的编码
- AAC的解码
- ACC的编码
2、添加头文件
- libavcodec/avcodec.h
3、常用数据结构
- AVCodec 编码器结构体
- AVCodecContext 编码器上下文
- AVFrame解码后端的帧
4、结构体内存的分配与释放
- av_frame_alloc()
- av_frame_free()
- avcodec_alloc_context3()
- avcodec_free_context()
5、解码步骤
- 查找解码器(avcodec_find_decoder)
- 打开解码器(avcodec_open2)
- 解码(avcodec_decode_video2)
6、H264编码流程
6.1 API简介
- 查找编码器(avcodec_find_encoder_by_name)
- 设置编码参数，并打开编码器(avcodec_open2)
- 编码(avcodec_encode_video2)
6.2 实例
从摄像头获取到的原始数据，就需要经过编码器编码，然后在网络上传输。
#include
#include
#include
#include
#include
#include
#include
#include
/* check that a given sample format is supported by the encoder */
static int check_sample_fmt(const AVCodec *codec, enum AVSampleFormat sample_fmt)
{
const enum AVSampleFormat *p = codec->sample_fmts;
while (*p != AV_SAMPLE_FMT_NONE) {
if (*p == sample_fmt)
return 1;
p++;
}
return 0;
}
/* just pick the highest supported samplerate */
static int select_sample_rate(const AVCodec *codec)
{
const int *p;
int best_samplerate = 0;
if (!codec->supported_samplerates)
return 44100;
p = codec->supported_samplerates;
while (*p) {
if (!best_samplerate || abs(44100 - *p) < abs(44100 - best_samplerate))
best_samplerate = *p;
p++;
}
return best_samplerate;
}
/* select layout with the highest channel count */
static int select_channel_layout(const AVCodec *codec)
{
const uint64_t *p;
uint64_t best_ch_layout = 0;
int best_nb_channels = 0;
if (!codec->channel_layouts)
return AV_CH_LAYOUT_STEREO;
p = codec->channel_layouts;
while (*p) {
int nb_channels = av_get_channel_layout_nb_channels(*p);
if (nb_channels > best_nb_channels) {
best_ch_layout = *p;
best_nb_channels = nb_channels;
}
p++;
}
return best_ch_layout;
}
int main(int argc, char **argv)
{
const char *filename;
const AVCodec *codec;
AVCodecContext *c= NULL;
AVFrame *frame;
AVPacket pkt;
int i, j, k, ret, got_output;
FILE *f;
uint16_t *samples;
float t, tincr;
if (argc <= 1) {
fprintf(stderr, "Usage: %s 6.3、编译
gcc -o test encode_video.c -lavformat -lavutil -lavcodec -I "/usr/local/ffmpeg/include/" -L "/usr/local/ffmpeg/lib/"
6.4、运行
./test 1.h264 libx264
7、视频转图片
7.1、代码实战
#include
#include
#include
#include
#include
#include
#define INBUF_SIZE 4096
#define WORD uint16_t
#define DWORD uint32_t
#define LONG int32_t
#pragma pack(2)
typedef struct tagBITMAPFILEHEADER {
WORD bfType;
DWORD bfSize;
WORD bfReserved1;
WORD bfReserved2;
DWORD bfOffBits;
} BITMAPFILEHEADER, *PBITMAPFILEHEADER;
typedef struct tagBITMAPINFOHEADER {
DWORD biSize;
LONG biWidth;
LONG biHeight;
WORD biPlanes;
WORD biBitCount;
DWORD biCompression;
DWORD biSizeImage;
LONG biXPelsPerMeter;
LONG biYPelsPerMeter;
DWORD biClrUsed;
DWORD biClrImportant;
} BITMAPINFOHEADER, *PBITMAPINFOHEADER;
void saveBMP(struct SwsContext *img_convert_ctx, AVFrame *frame, char *filename)
{
//1 先进行转换, YUV420=>RGB24:
int w = frame->width;
int h = frame->height;
int numBytes=avpicture_get_size(AV_PIX_FMT_BGR24, w, h);
uint8_t *buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
AVFrame *pFrameRGB = av_frame_alloc();
/* buffer is going to be written to rawvideo file, no alignment */
/*
if (av_image_alloc(pFrameRGB->data, pFrameRGB->linesize,
w, h, AV_PIX_FMT_BGR24, pix_fmt, 1) < 0) {
fprintf(stderr, "Could not allocate destination image\n");
exit(1);
}
*/
avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_BGR24, w, h);
sws_scale(img_convert_ctx, frame->data, frame->linesize,
0, h, pFrameRGB->data, pFrameRGB->linesize);
//2 构造 BITMAPINFOHEADER
BITMAPINFOHEADER header;
header.biSize = sizeof(BITMAPINFOHEADER);
header.biWidth = w;
header.biHeight = h*(-1);
header.biBitCount = 24;
header.biCompression = 0;
header.biSizeImage = 0;
header.biClrImportant = 0;
header.biClrUsed = 0;
header.biXPelsPerMeter = 0;
header.biYPelsPerMeter = 0;
header.biPlanes = 1;
//3 构造文件头
BITMAPFILEHEADER bmpFileHeader = {0,};
//HANDLE hFile = NULL;
DWORD dwTotalWriten = 0;
DWORD dwWriten;
bmpFileHeader.bfType = 0x4d42; //'BM';
bmpFileHeader.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER)+ numBytes;
bmpFileHeader.bfOffBits=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER);
FILE* pf = fopen(filename, "wb");
fwrite(&bmpFileHeader, sizeof(BITMAPFILEHEADER), 1, pf);
fwrite(&header, sizeof(BITMAPINFOHEADER), 1, pf);
fwrite(pFrameRGB->data[0], 1, numBytes, pf);
fclose(pf);
//释放资源
//av_free(buffer);
av_freep(&pFrameRGB[0]);
av_free(pFrameRGB);
}
static void pgm_save(unsigned char *buf, int wrap, int xsize, int ysize,
char *filename)
{
FILE *f;
int i;
f = fopen(filename,"w");
fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
for (i = 0; i < ysize; i++)
fwrite(buf + i * wrap, 1, xsize, f);
fclose(f);
}
static int decode_write_frame(const char *outfilename, AVCodecContext *avctx,
struct SwsContext *img_convert_ctx, AVFrame *frame, int *frame_count, AVPacket *pkt, int last)
{
int len, got_frame;
char buf[1024];
len = avcodec_decode_video2(avctx, frame, &got_frame, pkt);
if (len < 0) {
fprintf(stderr, "Error while decoding frame %d\n", *frame_count);
return len;
}
if (got_frame) {
printf("Saving %sframe %3d\n", last ? "last " : "", *frame_count);
fflush(stdout);
/* the picture is allocated by the decoder, no need to free it */
snprintf(buf, sizeof(buf), "%s-%d.bmp","test", *frame_count);
/*
pgm_save(frame->data[0], frame->linesize[0],
frame->width, frame->height, buf);
*/
saveBMP(img_convert_ctx, frame, buf);
(*frame_count)++;
}
if (pkt->data) {
pkt->size -= len;
pkt->data += len;
}
return 0;
}
int main(int argc, char **argv)
{
int ret;
FILE *f;
const char *filename, *outfilename;
AVFormatContext *fmt_ctx = NULL;
const AVCodec *codec;
AVCodecContext *c= NULL;
AVStream *st = NULL;
int stream_index;
int frame_count;
AVFrame *frame;
struct SwsContext *img_convert_ctx;
//uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
AVPacket avpkt;
if (argc <= 2) {
fprintf(stderr, "Usage: %s <1input file> 7.2、 编译
gcc -o test decode_video.c -lavformat -lavutil -lavcodec -lswscale -I "/usr/local/ffmpeg/include/" -L "/usr/local/ffmpeg/lib/"
7.3、运行
./test 1.h264 ./
有段错误，需要处理buff
8、ffmpeg AAC编码
8.1、编码流程
- 编码流程与视频相同
- 编码函数avcodec_encodec_audio2
8.2 、代码实例
#include
#include
#include
#include
#include
#include
#include
#include
/* check that a given sample format is supported by the encoder */
static int check_sample_fmt(const AVCodec *codec, enum AVSampleFormat sample_fmt)
{
const enum AVSampleFormat *p = codec->sample_fmts;
while (*p != AV_SAMPLE_FMT_NONE) {
if (*p == sample_fmt)
return 1;
p++;
}
return 0;
}
/* just pick the highest supported samplerate */
static int select_sample_rate(const AVCodec *codec)
{
const int *p;
int best_samplerate = 0;
if (!codec->supported_samplerates)
return 44100;
p = codec->supported_samplerates;
while (*p) {
if (!best_samplerate || abs(44100 - *p) < abs(44100 - best_samplerate))
best_samplerate = *p;
p++;
}
return best_samplerate;
}
/* select layout with the highest channel count */
static int select_channel_layout(const AVCodec *codec)
{
const uint64_t *p;
uint64_t best_ch_layout = 0;
int best_nb_channels = 0;
if (!codec->channel_layouts)
return AV_CH_LAYOUT_STEREO;
p = codec->channel_layouts;
while (*p) {
int nb_channels = av_get_channel_layout_nb_channels(*p);
if (nb_channels > best_nb_channels) {
best_ch_layout = *p;
best_nb_channels = nb_channels;
}
p++;
}
return best_ch_layout;
}
int main(int argc, char **argv)
{
const char *filename;
const AVCodec *codec;
AVCodecContext *c= NULL;
AVFrame *frame;
AVPacket pkt;
int i, j, k, ret, got_output;
FILE *f;
uint16_t *samples;
float t, tincr;
if (argc <= 1) {
fprintf(stderr, "Usage: %s 8.3、编译
gcc -o test encode_audio.c -lavutil -lavcodec -lm -I "/usr/local/ffmpeg/include/" -L "/usr/local/ffmpeg/lib/"
8.4 运行
./test 3.aac
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