Android NDK开发之旅–NDK-FFmpeg音频解码与播放

android ndk开发之旅30–ndk-ffmpeg音频解码与播放

音频解码实现

音频解码也是直接使用ffmpeg的api来做。

public native void sound(string input,string output);

其中，jni实现如下：

//重采样
#include "libswresample/swresample.h"

#define max_audio_frme_size 48000 * 4

jniexport void jnicall
java_com_nan_ffmpeg_utils_videoplayer_sound(jnienv *env, jobject instance, jstring input_,
                                            jstring output_) {
    const char *input = (*env)->getstringutfchars(env, input_, 0);
    const char *output = (*env)->getstringutfchars(env, output_, 0);

    //注册组件
    av_register_all();
    avformatcontext *pformatctx = avformat_alloc_context();
    //打开音频文件
    if (avformat_open_input(&pformatctx, input, null, null) != 0) {
        logi("%s", "无法打开音频文件");
        return;
    }
    //获取输入文件信息
    if (avformat_find_stream_info(pformatctx, null) < 0) {
        logi("%s", "无法获取输入文件信息");
        return;
    }
    //获取音频流索引位置
    int i = 0, audio_stream_idx = -1;
    for (; i < pformatctx->nb_streams; i++) {
        if (pformatctx->streams[i]->codec->codec_type == avmedia_type_audio) {
            audio_stream_idx = i;
            break;
        }
    }

    //获取解码器
    avcodeccontext *codecctx = pformatctx->streams[audio_stream_idx]->codec;
    avcodec *codec = avcodec_find_decoder(codecctx->codec_id);
    if (codec == null) {
        logi("%s", "无法获取解码器");
        return;
    }
    //打开解码器
    if (avcodec_open2(codecctx, codec, null) < 0) {
        logi("%s", "无法打开解码器");
        return;
    }
    //压缩数据
    avpacket *packet = (avpacket *) av_malloc(sizeof(avpacket));
    //解压缩数据
    avframe *frame = av_frame_alloc();
    //frame->16bit 44100 pcm 统一音频采样格式与采样率
    swrcontext *swrctx = swr_alloc();

    //重采样设置参数-------------start
    //输入的采样格式
    enum avsampleformat in_sample_fmt = codecctx->sample_fmt;
    //输出采样格式16bit pcm
    enum avsampleformat out_sample_fmt = av_sample_fmt_s16;
    //输入采样率
    int in_sample_rate = codecctx->sample_rate;
    //输出采样率
    int out_sample_rate = 44100;
    //获取输入的声道布局
    //根据声道个数获取默认的声道布局（2个声道，默认立体声stereo）
    //av_get_default_channel_layout(codecctx->channels);
    uint64_t in_ch_layout = codecctx->channel_layout;
    //输出的声道布局（立体声）
    uint64_t out_ch_layout = av_ch_layout_stereo;

    swr_alloc_set_opts(swrctx,
                       out_ch_layout, out_sample_fmt, out_sample_rate,
                       in_ch_layout, in_sample_fmt, in_sample_rate,
                       0, null);
    swr_init(swrctx);

    //输出的声道个数
    int out_channel_nb = av_get_channel_layout_nb_channels(out_ch_layout);

    //重采样设置参数-------------end

    //16bit 44100 pcm 数据
    uint8_t *out_buffer = (uint8_t *) av_malloc(max_audio_frme_size);

    file *fp_pcm = fopen(output, "wb");

    int got_frame = 0, index = 0, ret;
    //不断读取压缩数据
    while (av_read_frame(pformatctx, packet) >= 0) {
        //解码
        ret = avcodec_decode_audio4(codecctx, frame, &got_frame, packet);

        if (ret < 0) {
            logi("%s", "解码完成");
        }
        //解码一帧成功
        if (got_frame > 0) {
            logi("解码：%d", index++);
            swr_convert(swrctx, &out_buffer, max_audio_frme_size, frame->data, frame->nb_samples);
            //获取sample的size
            int out_buffer_size = av_samples_get_buffer_size(null, out_channel_nb,
                                                             frame->nb_samples, out_sample_fmt, 1);
            fwrite(out_buffer, 1, out_buffer_size, fp_pcm);
        }

        av_free_packet(packet);
    }

    fclose(fp_pcm);
    av_frame_free(&frame);
    av_free(out_buffer);

    swr_free(&swrctx);
    avcodec_close(codecctx);
    avformat_close_input(&pformatctx);

    (*env)->releasestringutfchars(env, input_, input);
    (*env)->releasestringutfchars(env, output_, output);
}

最终会输出pcm格式的文件。

音频播放

pcm音频播放的常用方法：

opensl rs audio track（webrtc就用到）

下面我们通过audio track来进行播放。

主要的实现思路就是：

在c层调用java层的createaudiotrack方法，创建audiotrack对象。 然后在c层调用audiotrack的pkay、write、stop等方法进行播放控制。

例子：

package com.nan.ffmpeg.utils;

public class videoplayer {

    static {
        system.loadlibrary("avutil-54");
        system.loadlibrary("swresample-1");
        system.loadlibrary("avcodec-56");
        system.loadlibrary("avformat-56");
        system.loadlibrary("swscale-3");
        system.loadlibrary("postproc-53");
        system.loadlibrary("avfilter-5");
        system.loadlibrary("avdevice-56");
        system.loadlibrary("ffmpeg-lib");
    }

    public native void render(string input, surface surface);

    public native void play(string input);

    /**
     * 创建一个audiotrac对象，用于播放
     *
     * @return
     */
    public audiotrack createaudiotrack(int samplerateinhz, int nb_channels) {
        //固定格式的音频码流
        int audioformat = audioformat.encoding_pcm_16bit;
        log.i("jason", "nb_channels:" + nb_channels);
        //声道布局
        int channelconfig;
        if (nb_channels == 1) {
            channelconfig = android.media.audioformat.channel_out_mono;
        } else if (nb_channels == 2) {
            channelconfig = android.media.audioformat.channel_out_stereo;
        } else {
            channelconfig = android.media.audioformat.channel_out_stereo;
        }

        int buffersizeinbytes = audiotrack.getminbuffersize(samplerateinhz, channelconfig, audioformat);

        audiotrack audiotrack = new audiotrack(
                audiomanager.stream_music,
                samplerateinhz, channelconfig,
                audioformat,
                buffersizeinbytes, audiotrack.mode_stream);
        //播放
        //audiotrack.play();
        //写入pcm
        //audiotrack.write(audiodata, offsetinbytes, sizeinbytes);
        //播放完调用stop即可

        audiotrack.stop();
        return audiotrack;
    }

}

jni实现如下：

//音频播放
jniexport void jnicall
java_com_nan_ffmpeg_utils_videoplayer_play(jnienv *env, jobject instance, jstring input_) {
    const char *input = (*env)->getstringutfchars(env, input_, 0);

    logi("%s", "sound");
    //注册组件
    av_register_all();
    avformatcontext *pformatctx = avformat_alloc_context();
    //打开音频文件
    if (avformat_open_input(&pformatctx, input, null, null) != 0) {
        logi("%s", "无法打开音频文件");
        return;
    }
    //获取输入文件信息
    if (avformat_find_stream_info(pformatctx, null) < 0) {
        logi("%s", "无法获取输入文件信息");
        return;
    }
    //获取音频流索引位置
    int i = 0, audio_stream_idx = -1;
    for (; i < pformatctx->nb_streams; i++) {
        if (pformatctx->streams[i]->codec->codec_type == avmedia_type_audio) {
            audio_stream_idx = i;
            break;
        }
    }

    //获取解码器
    avcodeccontext *codecctx = pformatctx->streams[audio_stream_idx]->codec;
    avcodec *codec = avcodec_find_decoder(codecctx->codec_id);
    if (codec == null) {
        logi("%s", "无法获取解码器");
        return;
    }
    //打开解码器
    if (avcodec_open2(codecctx, codec, null) < 0) {
        logi("%s", "无法打开解码器");
        return;
    }
    //压缩数据
    avpacket *packet = (avpacket *) av_malloc(sizeof(avpacket));
    //解压缩数据
    avframe *frame = av_frame_alloc();
    //frame->16bit 44100 pcm 统一音频采样格式与采样率
    swrcontext *swrctx = swr_alloc();

    //重采样设置参数-------------start
    //输入的采样格式
    enum avsampleformat in_sample_fmt = codecctx->sample_fmt;
    //输出采样格式16bit pcm
    enum avsampleformat out_sample_fmt = av_sample_fmt_s16;
    //输入采样率
    int in_sample_rate = codecctx->sample_rate;
    //输出采样率
    int out_sample_rate = in_sample_rate;
    //获取输入的声道布局
    //根据声道个数获取默认的声道布局（2个声道，默认立体声stereo）
    //av_get_default_channel_layout(codecctx->channels);
    uint64_t in_ch_layout = codecctx->channel_layout;
    //输出的声道布局（立体声）
    uint64_t out_ch_layout = av_ch_layout_stereo;

    swr_alloc_set_opts(swrctx,
                       out_ch_layout, out_sample_fmt, out_sample_rate,
                       in_ch_layout, in_sample_fmt, in_sample_rate,
                       0, null);
    swr_init(swrctx);

    //输出的声道个数
    int out_channel_nb = av_get_channel_layout_nb_channels(out_ch_layout);

    //重采样设置参数-------------end

    //jni begin------------------
    //jasonplayer
    jclass player_class = (*env)->getobjectclass(env, instance);

    //audiotrack对象
    jmethodid create_audio_track_mid = (*env)->getmethodid(env, player_class, "createaudiotrack",
                                                           "(ii)landroid/media/audiotrack;");
    jobject audio_track = (*env)->callobjectmethod(env, instance, create_audio_track_mid,
                                                   out_sample_rate, out_channel_nb);

    //调用audiotrack.play方法
    jclass audio_track_class = (*env)->getobjectclass(env, audio_track);
    jmethodid audio_track_play_mid = (*env)->getmethodid(env, audio_track_class, "play", "()v");
    jmethodid audio_track_stop_mid = (*env)->getmethodid(env, audio_track_class, "stop", "()v");
    (*env)->callvoidmethod(env, audio_track, audio_track_play_mid);

    //audiotrack.write
    jmethodid audio_track_write_mid = (*env)->getmethodid(env, audio_track_class, "write",
                                                          "([bii)i");
    //jni end------------------

    //16bit 44100 pcm 数据
    uint8_t *out_buffer = (uint8_t *) av_malloc(max_audio_frme_size);

    int got_frame = 0, index = 0, ret;
    //不断读取压缩数据
    while (av_read_frame(pformatctx, packet) >= 0) {
        //解码音频类型的packet
        if (packet->stream_index == audio_stream_idx) {
            //解码
            ret = avcodec_decode_audio4(codecctx, frame, &got_frame, packet);

            if (ret < 0) {
                logi("%s", "解码完成");
            }
            //解码一帧成功
            if (got_frame > 0) {
                logi("解码：%d", index++);
                swr_convert(swrctx, &out_buffer, max_audio_frme_size,
                            (const uint8_t **) frame->data, frame->nb_samples);
                //获取sample的size
                int out_buffer_size = av_samples_get_buffer_size(null, out_channel_nb,
                                                                 frame->nb_samples, out_sample_fmt,
                                                                 1);

                //out_buffer缓冲区数据，转成byte数组
                jbytearray audio_sample_array = (*env)->newbytearray(env, out_buffer_size);
                jbyte *sample_bytep = (*env)->getbytearrayelements(env, audio_sample_array, null);
                //out_buffer的数据复制到sampe_bytep
                memcpy(sample_bytep, out_buffer, out_buffer_size);
                //同步
                (*env)->releasebytearrayelements(env, audio_sample_array, sample_bytep, 0);

                //audiotrack.write pcm数据
                (*env)->callintmethod(env, audio_track, audio_track_write_mid,
                                      audio_sample_array, 0, out_buffer_size);
                //释放局部引用
                (*env)->deletelocalref(env, audio_sample_array);
            }
        }

        av_free_packet(packet);
    }

    (*env)->callvoidmethod(env, audio_track, audio_track_stop_mid);

    av_frame_free(&frame);
    av_free(out_buffer);

    swr_free(&swrctx);
    avcodec_close(codecctx);
    avformat_close_input(&pformatctx);

    (*env)->releasestringutfchars(env, input_, input);
}

测试：

@override
public void onclick(view v) {
    string inputvideo = environment.getexternalstoragedirectory().getabsolutepath() + file.separatorchar
            + “input.mp4”;

    string inputaudio = environment.getexternalstoragedirectory().getabsolutepath() + file.separatorchar
            + “love.mp3”;

    switch (v.getid()) {

        case r.id.btn_play_audio:

            mplayer.play(inputvideo);
            break;

    }
}