FFmpeg多媒体文件处理
【音视频】FFmpeg 安装+Api使用+Android+笔记( 二）
上一章节：
- FFmpeg 打印音/视频信息（Meta）
- FFmpeg 抽取音频数据
- FFmpeg 抽取H264视频频数据
- 介绍NALU单元
- 提取流程
- FFmpeg MP4转Flv
这一章节：
这一章节主要用到的FFmpeg模块知识：
重要头文件 :
libavcodec/avcodec.h
用到的函数 :
avcodec_register_all 把所有编解码器格式注册到程序中，形成一个列表
av_frame_get_buffer
使用该接口分配到的数据空间，是可复用的，即内部有引用计数（reference），本次对frame data使用完成， 可以解除引用，av_frame_unref(AVFrame *frame)，调用后，引用计数减1，如果引用计数变为0，则释放data 空间。当然，也可以添加引用，接口：av_frame_ref(AVFrame *dst, const AVFrame *src)。
重要结构体 :
1:AVCodec编解码结构体(作用：记录编解码的信息)
2:AVCodecContext 编解码上下文 (编解码媒体文件的上下文，表示对某个文件进行某种编码操作，调用Api的时候需要传入此上下文结构体)
3:AVFrame 解码后的帧 ( AVPackage 可能存在有多个帧，这些存在package里的帧都是压缩后的帧 ，解码后的帧则存在AVFrame)【从摄像头上获取的都是未压缩的帧，则可以存放在AVFrame】
结构体的额内存分配与释放 :
av_frame_alloc/av_frame_free AVFrame的分配与释放
avcodec_alloc_context3/avcodec_free _context AVCodecContext的分配与释放
解码步骤 :
1 : 查找解码器 (avcodec_find_decoder) 通过ID查找编解码器
2 : 打开解码器(avcodec_open2) 打开后解码器使能，后续才能做解码工作
3 : 解码(avcodec_decode_video2) 可以将一帧真压缩的数据解码成未压缩的数据，拿到未压缩数据进行渲染到Screen
编码步骤 :
1 : 查找解码器 ( avcodec_find_encoder_by_name) 的通过名字找到解码器(编码ID不容易记)
2 : 设置编码参数，打开编码器(avcodec_open2) [参数：视频宽高，分辨率，帧率等]
3 : 编码(avcodec_encode_ video2) 【音频编码(avcodec_encode_ audio2) 】
以上为视频编解码，音频编解码步骤与之相同。
注：解码程序为贴出，音视频实例代码都为编码操作
3.1 FFmpeg H264编解码
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libavcodec/avcodec.h>
#include <libavutil/opt.h>
#include <libavutil/imgutils.h>
int main(int argc, char **argv)
{
const char *filename, *codec_name;
const AVCodec *codec;
AVCodecContext *c= NULL;
int i, ret, x, y, got_output;
FILE *f;
AVFrame *frame;
AVPacket pkt;
uint8_t endcode[] = { 0, 0, 1, 0xb7 };
if (argc <= 2) {
fprintf(stderr, "Usage: %s <output file> <codec name>\n", argv[0]);
exit(0);
}
filename = argv[1];
codec_name = argv[2];
//把所有编解码器格式注册到程序中，形成一个列表
avcodec_register_all();
/* find the mpeg1video encoder */
codec = avcodec_find_encoder_by_name(codec_name);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
/* put sample parameters */
c->bit_rate = 400000;
/* resolution must be a multiple of two */
c->width = 352;
c->height = 288;
/* frames per second */
c->time_base = (AVRational){1, 25};
c->framerate = (AVRational){25, 1};
/* emit one intra frame every ten frames
* check frame pict_type before passing frame
* to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
* then gop_size is ignored and the output of encoder
* will always be I frame irrespective to gop_size
*/
//每多少帧出现关键帧
c->gop_size = 10;
c->max_b_frames = 1;
//原始的编码数据格式
c->pix_fmt = AV_PIX_FMT_YUV420P;
if (codec->id == AV_CODEC_ID_H264)
//H264编码设置参数集 ： slow 表示慢
av_opt_set(c->priv_data, "preset", "slow", 0);
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen(filename, "wb");
if (!f) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
//初始化avframe
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
//设置参数 参数可用从原始文件的上下文读取
frame->format = c->pix_fmt;
frame->width = c->width;
frame->height = c->height;
/** 使用该接口分配到的数据空间，是可复用的，即内部有引用计数（reference），本次对frame data使用完成，
* 可以解除引用，av_frame_unref(AVFrame *frame)，调用后，引用计数减1，如果引用计数变为0，则释放data
* 空间。当然，也可以添加引用，接口：av_frame_ref(AVFrame *dst, const AVFrame *src)。 **/
ret = av_frame_get_buffer(frame, 32);
if (ret < 0) {
fprintf(stderr, "Could not allocate the video frame data\n");
exit(1);
}
/* encode 1 second of video */
for (i = 0; i < 25; i++) {
//初始化pkt
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
fflush(stdout);
/* make sure the frame data is writable */
ret = av_frame_make_writable(frame);
if (ret < 0)
exit(1);
/*以下2个for为模拟数据，真实可用根据实际业务 如摄像头读取数据存放在frame 在进行编码压缩*/
/* prepare a dummy image */
/* Y */
for (y = 0; y < c->height; y++) {
for (x = 0; x < c->width; x++) {
frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
}
}
/* Cb and Cr */
for (y = 0; y < c->height/2; y++) {
for (x = 0; x < c->width/2; x++) {
frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
}
}
frame->pts = i;
/* encode the image */
//frame 是未压缩的数据，从原始视频文件中读取的 got_output判断是否压缩成功，pkt 存放压缩后的数据
ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
//got_output 为1 则就说明 压缩好了1帧
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
//将 存放在pkt上的压缩文件 写入文件中
fwrite(pkt.data, 1, pkt.size, f);
av_packet_unref(&pkt);
}
}
/* get the delayed frames */
for (got_output = 1; got_output; i++) {
fflush(stdout);
ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
fwrite(pkt.data, 1, pkt.size, f);
av_packet_unref(&pkt);
}
}
/* add sequence end code to have a real MPEG file */
fwrite(endcode, 1, sizeof(endcode), f);
fclose(f);
avcodec_free_context(&c);
av_frame_free(&frame);
return 0;
}
3.1 FFmpeg ACC音频 编解码
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <libavcodec/avcodec.h>
#include <libavutil/channel_layout.h>
#include <libavutil/common.h>
#include <libavutil/frame.h>
#include <libavutil/samplefmt.h>
/* 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 <output file>\n", argv[0]);
return 0;
}
filename = argv[1];
/* register all the codecs */
avcodec_register_all();
/* find the MP2 encoder 查找编解码器*/
codec = avcodec_find_encoder(AV_CODEC_ID_MP2);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
//初始化codec 上下文
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate audio codec context\n");
exit(1);
}
//设置音频参数 和视频步骤一致
/* put sample parameters */
c->bit_rate = 64000;
/* check that the encoder supports s16 pcm input */
c->sample_fmt = AV_SAMPLE_FMT_S16;
if (!check_sample_fmt(codec, c->sample_fmt)) {
fprintf(stderr, "Encoder does not support sample format %s",
av_get_sample_fmt_name(c->sample_fmt));
exit(1);
}
/* select other audio parameters supported by the encoder */
c->sample_rate = select_sample_rate(codec);
c->channel_layout = select_channel_layout(codec);
c->channels = av_get_channel_layout_nb_channels(c->channel_layout);
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen(filename, "wb");
if (!f) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
/* frame containing input raw audio */
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate audio frame\n");
exit(1);
}
frame->nb_samples = c->frame_size;
frame->format = c->sample_fmt;
frame->channel_layout = c->channel_layout;
/* allocate the data buffers */
ret = av_frame_get_buffer(frame, 0);
if (ret < 0) {
fprintf(stderr, "Could not allocate audio data buffers\n");
exit(1);
}
/* encode a single tone sound */
t = 0;
tincr = 2 * M_PI * 440.0 / c->sample_rate;
/**
以下是模拟一段音频数据，真正的数据如从麦克风采集PCM数据
**/
for (i = 0; i < 200; i++) {
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
/* make sure the frame is writable -- makes a copy if the encoder
* kept a reference internally */
ret = av_frame_make_writable(frame);
if (ret < 0)
exit(1);
samples = (uint16_t*)frame->data[0];
for (j = 0; j < c->frame_size; j++) {
samples[2*j] = (int)(sin(t) * 10000);
for (k = 1; k < c->channels; k++)
samples[2*j + k] = samples[2*j];
t += tincr;
}
/* encode the samples */
ret = avcodec_encode_audio2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding audio frame\n");
exit(1);
}
if (got_output) {
fwrite(pkt.data, 1, pkt.size, f);
av_packet_unref(&pkt);
}
}
/* get the delayed frames */
for (got_output = 1; got_output; i++) {
ret = avcodec_encode_audio2(c, &pkt, NULL, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
fwrite(pkt.data, 1, pkt.size, f);
av_packet_unref(&pkt);
}
}
fclose(f);
av_frame_free(&frame);
avcodec_free_context(&c);
return 0;
}
3.1 FFmpeg 视频转图片实战
1：找到对应原始文件的编解码器
2：打开解码器将视频压缩的帧 解码后形成一帧一帧的图片
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
#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", outfilename, *frame_count);
/*
pgm_save(frame->data[0], frame->linesize[0],
frame->width, frame->height, buf);
*/
saveBMP(img_convert_ctx, frame, buf);
(*frame_count)++;
}
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 <input file> <output file>\n", argv[0]);
exit(0);
}
filename = argv[1];
outfilename = argv[2];
/* register all formats and codecs */
av_register_all();
/* open input file, and allocate format context */
if (avformat_open_input(&fmt_ctx, filename, NULL, NULL) < 0) {
fprintf(stderr, "Could not open source file %s\n", filename);
exit(1);
}
/* retrieve stream information */
if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
fprintf(stderr, "Could not find stream information\n");
exit(1);
}
/* dump input information to stderr */
av_dump_format(fmt_ctx, 0, filename, 0);
av_init_packet(&avpkt);
/* set end of buffer to 0 (this ensures that no overreading happens for damaged MPEG streams) */
//memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
//
ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
if (ret < 0) {
fprintf(stderr, "Could not find %s stream in input file '%s'\n",
av_get_media_type_string(AVMEDIA_TYPE_VIDEO), filename);
return ret;
}
stream_index = ret;
st = fmt_ctx->streams[stream_index];
/* find decoder for the stream */
codec = avcodec_find_decoder(st->codecpar->codec_id);
if (!codec) {
fprintf(stderr, "Failed to find %s codec\n",
av_get_media_type_string(AVMEDIA_TYPE_VIDEO));
return AVERROR(EINVAL);
}
/* find the MPEG-1 video decoder */
/*
codec = avcodec_find_decoder(AV_CODEC_ID_MPEG1VIDEO);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
*/
c = avcodec_alloc_context3(NULL);
if (!c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
/* Copy codec parameters from input stream to output codec context */
if ((ret = avcodec_parameters_to_context(c, st->codecpar)) < 0) {
fprintf(stderr, "Failed to copy %s codec parameters to decoder context\n",
av_get_media_type_string(AVMEDIA_TYPE_VIDEO));
return ret;
}
/*
if (codec->capabilities & AV_CODEC_CAP_TRUNCATED)
c->flags |= AV_CODEC_FLAG_TRUNCATED; // we do not send complete frames
*/
/* For some codecs, such as msmpeg4 and mpeg4, width and height
MUST be initialized there because this information is not
available in the bitstream. */
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
/*
f = fopen(filename, "rb");
if (!f) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
*/
img_convert_ctx = sws_getContext(c->width, c->height,
c->pix_fmt,
c->width, c->height,
AV_PIX_FMT_BGR24,
SWS_BICUBIC, NULL, NULL, NULL);
if (img_convert_ctx == NULL)
{
fprintf(stderr, "Cannot initialize the conversion context\n");
exit(1);
}
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
frame_count = 0;
while (av_read_frame(fmt_ctx, &avpkt) >= 0) {
/*
avpkt.size = fread(inbuf, 1, INBUF_SIZE, f);
if (avpkt.size == 0)
break;
*/
/* NOTE1: some codecs are stream based (mpegvideo, mpegaudio)
and this is the only method to use them because you cannot
know the compressed data size before analysing it.
BUT some other codecs (msmpeg4, mpeg4) are inherently frame
based, so you must call them with all the data for one
frame exactly. You must also initialize 'width' and
'height' before initializing them. */
/* NOTE2: some codecs allow the raw parameters (frame size,
sample rate) to be changed at any frame. We handle this, so
you should also take care of it */
/* here, we use a stream based decoder (mpeg1video), so we
feed decoder and see if it could decode a frame */
//avpkt.data = inbuf;
//while (avpkt.size > 0)
if(avpkt.stream_index == stream_index){
if (decode_write_frame(outfilename, c, img_convert_ctx, frame, &frame_count, &avpkt, 0) < 0)
exit(1);
}
av_packet_unref(&avpkt);
}
/* Some codecs, such as MPEG, transmit the I- and P-frame with a
latency of one frame. You must do the following to have a
chance to get the last frame of the video. */
avpkt.data = NULL;
avpkt.size = 0;
decode_write_frame(outfilename, c, img_convert_ctx, frame, &frame_count, &avpkt, 1);
fclose(f);
avformat_close_input(&fmt_ctx);
sws_freeContext(img_convert_ctx);
avcodec_free_context(&c);
av_frame_free(&frame);
return 0;
}