FFmpeg多媒體文件處理
【音視頻】FFmpeg 安裝+Api使用+Android+筆記( 二）
上一章節：
- FFmpeg 打印音/視頻信息（Meta）
- FFmpeg 抽取音頻數據
- FFmpeg 抽取H264視頻頻數據
- 介紹NALU單元
- 提取流程
- FFmpeg MP4轉Flv
這一章節：
這一章節主要用到的FFmpeg模塊知識：
重要頭文件 :
libavcodec/avcodec.h
用到的函數 :
avcodec_register_all 把所有編解碼器格式註冊到程序中，形成一個列表
av_frame_get_buffer
使用該接口分配到的數據空間，是可複用的，即內部有引用計數（reference），本次對frame data使用完成， 可以解除引用，av_frame_unref(AVFrame *frame)，調用後，引用計數減1，如果引用計數變爲0，則釋放data 空間。當然，也可以添加引用，接口：av_frame_ref(AVFrame *dst, const AVFrame *src)。
重要結構體 :
1:AVCodec編解碼結構體(作用：記錄編解碼的信息)
2:AVCodecContext 編解碼上下文 (編解碼媒體文件的上下文，表示對某個文件進行某種編碼操作，調用Api的時候需要傳入此上下文結構體)
3:AVFrame 解碼後的幀 ( AVPackage 可能存在有多個幀，這些存在package裏的幀都是壓縮後的幀 ，解碼後的幀則存在AVFrame)【從攝像頭上獲取的都是未壓縮的幀，則可以存放在AVFrame】
結構體的額內存分配與釋放 :
av_frame_alloc/av_frame_free AVFrame的分配與釋放
avcodec_alloc_context3/avcodec_free _context AVCodecContext的分配與釋放
解碼步驟 :
1 : 查找解碼器 (avcodec_find_decoder) 通過ID查找編解碼器
2 : 打開解碼器(avcodec_open2) 打開後解碼器使能，後續才能做解碼工作
3 : 解碼(avcodec_decode_video2) 可以將一幀真壓縮的數據解碼成未壓縮的數據，拿到未壓縮數據進行渲染到Screen
編碼步驟 :
1 : 查找解碼器 ( avcodec_find_encoder_by_name) 的通過名字找到解碼器(編碼ID不容易記)
2 : 設置編碼參數，打開編碼器(avcodec_open2) [參數：視頻寬高，分辨率，幀率等]
3 : 編碼(avcodec_encode_ video2) 【音頻編碼(avcodec_encode_ audio2) 】
以上爲視頻編解碼，音頻編解碼步驟與之相同。
注：解碼程序爲貼出，音視頻實例代碼都爲編碼操作
3.1 FFmpeg H264編解碼
#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];
//把所有編解碼器格式註冊到程序中，形成一個列表
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
*/
//每多少幀出現關鍵幀
c->gop_size = 10;
c->max_b_frames = 1;
//原始的編碼數據格式
c->pix_fmt = AV_PIX_FMT_YUV420P;
if (codec->id == AV_CODEC_ID_H264)
//H264編碼設置參數集 ： 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);
}
//設置參數 參數可用從原始文件的上下文讀取
frame->format = c->pix_fmt;
frame->width = c->width;
frame->height = c->height;
/** 使用該接口分配到的數據空間，是可複用的，即內部有引用計數（reference），本次對frame data使用完成，
* 可以解除引用，av_frame_unref(AVFrame *frame)，調用後，引用計數減1，如果引用計數變爲0，則釋放data
* 空間。當然，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個for爲模擬數據，真實可用根據實際業務 如攝像頭讀取數據存放在frame 在進行編碼壓縮*/
/* 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 是未壓縮的數據，從原始視頻文件中讀取的 got_output判斷是否壓縮成功，pkt 存放壓縮後的數據
ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
//got_output 爲1 則就說明 壓縮好了1幀
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
//將 存放在pkt上的壓縮文件 寫入文件中
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音頻 編解碼
#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 查找編解碼器*/
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);
}
//設置音頻參數 和視頻步驟一致
/* 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;
/**
以下是模擬一段音頻數據，真正的數據如從麥克風採集PCM數據
**/
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 視頻轉圖片實戰
1：找到對應原始文件的編解碼器
2：打開解碼器將視頻壓縮的幀 解碼後形成一幀一幀的圖片
#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 先進行轉換, 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 構造 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 構造文件頭
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);
//釋放資源
//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;
}