一般ffmpeg都是直接从文件中读取或者从网络流中读取，比如rtp://xx.xx.xx.xx:xxxx。
事实上也支持从内存中获取。
函数avio_alloc_context()实现该功能。
- AVIOContext *avio_alloc_context(
- unsigned char *buffer,
- int buffer_size,
- int write_flag,
- void *opaque,
- int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),//重写该函数，指定从内存中读取的方法，将buf_size字节大小的数据保存到buf
- int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),//对应的这是写内存的函数
- int64_t (*seek)(void *opaque, int64_t offset, int whence));
对于探测网络媒体流个格式，也可以用此种方法，先接收数据，然后探测。
下面贴出代码：
- /*
- *author tongli
- */
- extern "C"{
- #include "libavformat/avformat.h"
- #include "libavcodec/avcodec.h"
- #include "libavutil/avutil.h"
- }
- #define BUF_SIZE 4096*500
- FILE* file;
- //实现read_packet函数，从文件中读取模拟的是从内存中获取，同样可以实现为接收网络流
- int read_packet(void *opaque, uint8_t *buf, int buf_size)
- {
- int n = 0;
- if (!feof(file)){
- n = fread(buf, 1, buf_size, file);
- return n;
- }else
- return -1;
- }
- int main(int argc, char** argv)
- {
- file = fopen("2.mp4", "rb");
- if (file == NULL)
- return -1;
- av_register_all();
- AVIOContext* pb = NULL;
- AVInputFormat* piFmt = NULL;
- AVInputFormat* pFmt = NULL;
- uint8_t* buf = (uint8_t*)av_mallocz(sizeof(uint8_t)* BUF_SIZE);
- pb = avio_alloc_context(buf, BUF_SIZE, 0, NULL, read_packet, NULL, NULL);
- if (av_probe_input_buffer(pb, &piFmt, "", NULL, 0, 0) < 0)//探测从内存中获取到的媒体流的格式
- {
- fprintf(stderr, "probe format failed\n");
- return -1;
- }
- else{
- fprintf(stdout, "format:%s[%s]\n", piFmt->name, piFmt->long_name);
- }
- return 0;
- }
下面实现一个简单的例子，从内存中读取，然后播放。
-
- <pre name="code" class="cpp">/*
- *author tongli
- */
- #include <stdio.h>
- #include <direct.h>
- #include <io.h>
- extern "C"{
- #include "libavformat/avformat.h"
- #include "libavcodec/avcodec.h"
- #include "libavutil/avutil.h"
- #include "libswscale/swscale.h"
- #include "libavformat/avio.h"
- #include "sdl/SDL.h"
- }
- #define BUF_SIZE 4096 * 500
- FILE* file;
- int read_data(void *opaque, uint8_t *buf, int buf_size)
- {
- int n = 0;
- if (!feof(file)){
- n = fread(buf, 1, buf_size, file);
- return n;
- }
- else
- return -1;
- }
- int main(int argc, char* argv[])
- {
- av_register_all();
- //file = fopen("h2.dat", "rb");
- file = fopen("3.mp4", "rb+");
- if (file == NULL)
- return -1;
- AVFormatContext *pFormatCtx;
- int i, videoindex;
- AVCodecContext *pCodecCtx;
- AVCodec *pCodec;
- AVIOContext* pb = NULL;
- AVInputFormat* piFmt = NULL;
- uint8_t* buf = (uint8_t*)av_mallocz(sizeof(uint8_t)* BUF_SIZE);
- pb = avio_alloc_context(buf, BUF_SIZE, 0, NULL, read_data, NULL, NULL);
- if (av_probe_input_buffer(pb, &piFmt, "", NULL, 0, 0) < 0)
- {
- fprintf(stderr, "probe format failed\n");
- return -1;
- }
- else{
- fprintf(stdout, "format:%s[%s]\n", piFmt->name, piFmt->long_name);
- }
- pFormatCtx = avformat_alloc_context();
- pFormatCtx->pb = pb;
- if (avformat_open_input(&pFormatCtx, "", piFmt, NULL) != 0){//iformat，priv_data赋值，pb, nbstreams,streams为null
- printf("Couldn't open input stream.（无法打开输入流）\n");
- return -1;
- }
- if (avformat_find_stream_info(pFormatCtx, NULL)<0)//nbstreams,streams赋值， pb还是为null
- {
- printf("Couldn't find stream information.（无法获取流信息）\n");
- return -1;
- }
- videoindex = -1;
- for (i = 0; i<pFormatCtx->nb_streams; i++) //一般情况下，一个媒体只有两个流，视频和音频流即streams[0],stream[1]
- if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
- {//找到视频流
- videoindex = i;//在nb_streams视频流的索引
- break;
- }
- if (videoindex == -1)
- {
- printf("Didn't find a video stream.（没有找到视频流）\n");
- return -1;
- }
- pCodecCtx = pFormatCtx->streams[videoindex]->codec;
- pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
- if (pCodec == NULL)
- {
- printf("Codec not found.（没有找到解码器）\n");
- return -1;
- }
- if (avcodec_open2(pCodecCtx, pCodec, NULL)<0)
- {
- printf("Could not open codec.（无法打开解码器）\n");
- return -1;
- }
- AVFrame *pFrame, *pFrameYUV;
- pFrame = av_frame_alloc();
- pFrameYUV = av_frame_alloc();
- uint8_t *out_buffer;
- out_buffer = new uint8_t[avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height)];
- avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);
- //------------SDL----------------
- if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
- printf("Could not initialize SDL - %s\n", SDL_GetError());
- return -1;
- }
- SDL_Surface *screen;
- screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 0, 0);
- if (!screen) {
- printf("SDL: could not set video mode - exiting\n");
- return -1;
- }
- SDL_Overlay *bmp;
- bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height, SDL_YV12_OVERLAY, screen);
- SDL_Rect rect;
- //---------------
- int ret, got_picture;
- int y_size = pCodecCtx->width * pCodecCtx->height;
- AVPacket *packet = (AVPacket *)av_malloc(sizeof(AVPacket));
- av_new_packet(packet, y_size);
- struct SwsContext *img_convert_ctx;
- img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
- AV_PIX_FMT_YUVJ420P/*pCodecCtx->pix_fmt*/, pCodecCtx->width, pCodecCtx->height,
- PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
- //------------------------------
- while (av_read_frame(pFormatCtx, packet) >= 0)
- {
- if (packet->stream_index == videoindex)
- {
- ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
- if (ret < 0)
- {
- printf("Decode Error.（解码错误）\n");
- return -1;
- }
- if (got_picture)
- {
- sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
- SDL_LockYUVOverlay(bmp);
- bmp->pixels[0] = pFrameYUV->data[0];
- bmp->pixels[2] = pFrameYUV->data[1];
- bmp->pixels[1] = pFrameYUV->data[2];
- bmp->pitches[0] = pFrameYUV->linesize[0];
- bmp->pitches[2] = pFrameYUV->linesize[1];
- bmp->pitches[1] = pFrameYUV->linesize[2];
- SDL_UnlockYUVOverlay(bmp);
- rect.x = 0;
- rect.y = 0;
- rect.w = pCodecCtx->width;
- rect.h = pCodecCtx->height;
- SDL_DisplayYUVOverlay(bmp, &rect);
- //延时40ms
- SDL_Delay(40);
- }
- }
- av_free_packet(packet);
- }
- sws_freeContext(img_convert_ctx);
- delete[] out_buffer;
- av_free(pFrameYUV);
- avcodec_close(pCodecCtx);
- avformat_close_input(&pFormatCtx);
- return 0;
- }
