Android NDK开发之旅30–NDK-FFmpeg音频解码与播放

超、凢脫俗 2022-05-28 03:53 156阅读 0赞

# 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：

1.  OpenSL RS
2.  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：

1.  在C层调用Java层的createAudioTrack方法，创建AudioTrack对象。
2.  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; } }