[原]如何在Android用FFmpeg+SDL2.0解码声音

关于如何在Android上用FFmpeg+SDL2.0解码显示图像参考[原]如何在Android用FFmpeg+SDL2.0解码显示图像，本文是基于上述文章和[原]零基础学习视频解码之解码声音来移植到Android设备上的，也是参考http://dranger.com/ffmpeg/tutorial03.html来编写的。只不过dranger的文章比较老了，FFmpeg很多接口变了，因此采用了最新的接口替换，并且采用FFmpeg+SDL2.0来做解码和输出。

博主的开发环境：Ubuntu 14.04 64位，Eclipse+CDT+ADT+NDK。

在文章开始之前假定你已经知道如何使用NDK编译FFmpeg，以及知道如何移植SDL2.0到Android平台上来并且知道如何解码显示图像了，如有不明白的可以参考文章开头的两篇文章。

工程中的目录结构和[原]如何在Android用FFmpeg+SDL2.0解码显示图像一样，只是在其基础上继续添加功能而已。解码声音的原理可以参考http://dranger.com/ffmpeg/tutorial03.html

下面直接给出解码声音的代码内容：

/* * SDL_Lesson.c * *  Created on: Aug 12, 2014 *      Author: clarck */#include <jni.h>#include <android/native_window_jni.h>#include "SDL.h"#include "SDL_thread.h"#include "SDL_events.h"#include "../include/logger.h"#include "../ffmpeg/include/libavcodec/avcodec.h"#include "../ffmpeg/include/libavformat/avformat.h"#include "../ffmpeg/include/libavutil/pixfmt.h"#include "../ffmpeg/include/libswscale/swscale.h"#define SDL_AUDIO_BUFFER_SIZE 1024#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audiotypedef struct PacketQueue {    AVPacketList *first_pkt, *last_pkt;    int nb_packets;    int size;    SDL_mutex *mutex;    SDL_cond *cond;} PacketQueue;PacketQueue audioq;int quit = 0;void packet_queue_init(PacketQueue *q) {    memset(q, 0, sizeof(PacketQueue));    q->mutex = SDL_CreateMutex();    q->cond = SDL_CreateCond();}int packet_queue_put(PacketQueue *q, AVPacket *pkt) {    AVPacketList *pkt1;    if (av_dup_packet(pkt) < 0) {        return -1;    }    pkt1 = av_malloc(sizeof(AVPacketList));    if (!pkt1)        return -1;    pkt1->pkt = *pkt;    pkt1->next = NULL;    SDL_LockMutex(q->mutex);    if (!q->last_pkt)        q->first_pkt = pkt1;    else        q->last_pkt->next = pkt1;    q->last_pkt = pkt1;    q->nb_packets++;    q->size += pkt1->pkt.size;    SDL_CondSignal(q->cond);    SDL_UnlockMutex(q->mutex);    return 0;}static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {    AVPacketList *pkt1;    int ret;    SDL_LockMutex(q->mutex);    for (;;) {        if (quit) {            ret = -1;            break;        }        pkt1 = q->first_pkt;        if (pkt1) {            q->first_pkt = pkt1->next;            if (!q->first_pkt)                q->last_pkt = NULL;            q->nb_packets--;            q->size -= pkt1->pkt.size;            *pkt = pkt1->pkt;            av_free(pkt1);            ret = 1;            break;        } else if (!block) {            ret = 0;            break;        } else {            SDL_CondWait(q->cond, q->mutex);        }    }    SDL_UnlockMutex(q->mutex);    return ret;}int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,        int buf_size) {    static AVPacket pkt;    static uint8_t *audio_pkt_data = NULL;    static int audio_pkt_size = 0;    static AVFrame frame;    int len1, data_size = 0;    for (;;) {        while (audio_pkt_size > 0) {            int got_frame = 0;            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);            if (len1 < 0) {                /* if error, skip frame */                audio_pkt_size = 0;                break;            }            audio_pkt_data += len1;            audio_pkt_size -= len1;            if (got_frame) {                data_size = frame.linesize[0];                /*                 data_size = av_samples_get_buffer_size(NULL,                 aCodecCtx->channels, frame.nb_samples,                 aCodecCtx->sample_fmt, 1);                 */                memcpy(audio_buf, frame.data[0], data_size);            }            if (data_size <= 0) {                /* No data yet, get more frames */                continue;            }            /* We have data, return it and come back for more later */            return data_size;        }        if (pkt.data)            av_free_packet(&pkt);        if (quit) {            return -1;        }        if (packet_queue_get(&audioq, &pkt, 1) < 0) {            return -1;        }        audio_pkt_data = pkt.data;        audio_pkt_size = pkt.size;    }    return 0;}void audio_callback(void *userdata, Uint8 *stream, int len) {    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;    int len1, audio_size;    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];    static unsigned int audio_buf_size = 0;    static unsigned int audio_buf_index = 0;    while (len > 0) {        if (audio_buf_index >= audio_buf_size) {            /* We have already sent all our data; get more */            audio_size = audio_decode_frame(aCodecCtx, audio_buf,                    sizeof(audio_buf));            if (audio_size < 0) {                /* If error, output silence */                audio_buf_size = 1024; // arbitrary?                memset(audio_buf, 0, audio_buf_size);            } else {                audio_buf_size = audio_size;            }            audio_buf_index = 0;        }        len1 = audio_buf_size - audio_buf_index;        if (len1 > len)            len1 = len;        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);        len -= len1;        stream += len1;        audio_buf_index += len1;    }}int main(int argc, char *argv[]) {    char *file_path = argv[1];    LOGI("file_path:%s", file_path);    AVFormatContext *pFormatCtx;    AVCodecContext *pCodecCtx;    AVCodec *pCodec;    AVFrame *pFrame, *pFrameYUV;    AVPacket *packet;    uint8_t *out_buffer;    AVCodecContext *aCodecCtx;    AVCodec *aCodec;    SDL_Texture *bmp = NULL;    SDL_Window *screen = NULL;    SDL_Rect rect;    SDL_Event event;    SDL_AudioSpec wanted_spec, spec;    static struct SwsContext *img_convert_ctx;    int videoStream, audioStream, i, numBytes;    int ret, got_picture;    av_register_all();    pFormatCtx = avformat_alloc_context();    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {        LOGE("Could not initialize SDL - %s. \n", SDL_GetError());        exit(1);    }    if (avformat_open_input(&pFormatCtx, file_path, NULL, NULL) != 0) {        LOGE("can't open the file. \n");        return -1;    }    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {        LOGE("Could't find stream infomation.\n");        return -1;    }    videoStream = 1;    audioStream = -1;    for (i = 0; i < pFormatCtx->nb_streams; i++) {        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {            videoStream = i;        }        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO                && audioStream < 0) {            audioStream = i;        }    }    LOGI("videoStream:%d", videoStream);    if (videoStream == -1) {        LOGE("Didn't find a video stream.\n");        return -1;    }    if (audioStream == -1) {        LOGE("Didn't find a audio stream.\n");        return -1;    }    aCodecCtx = pFormatCtx->streams[audioStream]->codec;    // Set audio settings from codec info    wanted_spec.freq = aCodecCtx->sample_rate;    wanted_spec.format = AUDIO_S16SYS;    wanted_spec.channels = aCodecCtx->channels;    wanted_spec.silence = 0;    wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;    wanted_spec.callback = audio_callback;    wanted_spec.userdata = aCodecCtx;    if (SDL_OpenAudio(&wanted_spec, &spec) < 0) {        LOGE("SDL_OpenAudio: %s\n", SDL_GetError());        return -1;    }    aCodec = avcodec_find_decoder(aCodecCtx->codec_id);    if (!aCodec) {        LOGE("Unsupported codec!\n");        return -1;    }    avcodec_open2(aCodecCtx, aCodec, NULL);    // audio_st = pFormatCtx->streams[index]    packet_queue_init(&audioq);    SDL_PauseAudio(0);    pCodecCtx = pFormatCtx->streams[videoStream]->codec;    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);    if (pCodec == NULL) {        LOGE("Codec not found.\n");        return -1;    }    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {        LOGE("Could not open codec.\n");        return -1;    }    pFrame = av_frame_alloc();    pFrameYUV = av_frame_alloc();    //---------------------------init sdl---------------------------//    screen = SDL_CreateWindow("My Player Window", SDL_WINDOWPOS_UNDEFINED,            SDL_WINDOWPOS_UNDEFINED, pCodecCtx->width, pCodecCtx->height,            SDL_WINDOW_FULLSCREEN | SDL_WINDOW_OPENGL);    SDL_Renderer *renderer = SDL_CreateRenderer(screen, -1, 0);    bmp = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_YV12,            SDL_TEXTUREACCESS_STREAMING, pCodecCtx->width, pCodecCtx->height);    //-------------------------------------------------------------//    numBytes = avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width,            pCodecCtx->height);    out_buffer = (uint8_t *) av_malloc(numBytes * sizeof(uint8_t));    avpicture_fill((AVPicture *) pFrameYUV, out_buffer, AV_PIX_FMT_YUV420P,            pCodecCtx->width, pCodecCtx->height);    rect.x = 0;    rect.y = 0;    rect.w = pCodecCtx->width;    rect.h = pCodecCtx->height;    int y_size = pCodecCtx->width * pCodecCtx->height;    packet = (AVPacket *) malloc(sizeof(AVPacket));    av_new_packet(packet, y_size);    av_dump_format(pFormatCtx, 0, file_path, 0);    while (av_read_frame(pFormatCtx, packet) >= 0) {        if (packet->stream_index == videoStream) {            ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture,                    packet);            if (ret < 0) {                LOGE("decode error.\n");                return -1;            }            LOGI("got_picture:%d", got_picture);            if (got_picture) {                img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,                            pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,                            AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);                sws_scale(img_convert_ctx,                        (uint8_t const * const *) pFrame->data,                        pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data,                        pFrameYUV->linesize);                sws_freeContext(img_convert_ctx);                ////iPitch 计算yuv一行数据占的字节数                SDL_UpdateYUVTexture(bmp, &rect,                        pFrameYUV->data[0], pFrameYUV->linesize[0],                        pFrameYUV->data[1], pFrameYUV->linesize[1],                        pFrameYUV->data[2], pFrameYUV->linesize[2]);                SDL_RenderClear(renderer);                SDL_RenderCopy(renderer, bmp, &rect, &rect);                SDL_RenderPresent(renderer);            }            av_free_packet(packet);        } else if (packet->stream_index == audioStream) {            packet_queue_put(&audioq, packet);        } else {            av_free_packet(packet);        }        SDL_PollEvent(&event);        switch (event.type) {        case SDL_QUIT:            SDL_Quit();            exit(0);            break;        default:            break;        }    }    SDL_DestroyTexture(bmp);    av_free(out_buffer);    av_free(pFrameYUV);    avcodec_close(pCodecCtx);    avformat_close_input(&pFormatCtx);    return 0;}

这里看到的图像比较快以及声音和图像不同步，且声音噪音很大。原因是没有做声音和图像的同步处理，这里不同步也很正常。关于噪音很大，是有一个小细节的处理不到位造成的。

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