ffmpeg AV_SAMPLE_FMT_FLTP to AV_SAMPLE_FMT_S16

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本文介绍如何使用FFmpeg 2.0将不兼容的音频格式AV_SAMPLE_FMT_FLTP转换为Android支持的AV_SAMPLE_FMT_S16。通过创建SwrContext上下文并调用swr_convert进行重采样。

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ffmpeg 2.0 音频解码出来的数据格式不符合Android音频格式

问题原因：

ffmpeg2.0最新的解码出来的数据是sample_fmts = AV_SAMPLE_FMT_FLTP

android需要的音频格式：sample_fmts (AV_SAMPLE_FMT_S8, AV_SAMPLE_FMT_S16)

解决方法：

1，创建转换对象

void audio_swr_resampling_audio_init(SwrContext**swr_ctx,TargetAudioParams *targetAudioParams,AVCodecContext *codec){

if(codec->sample_fmt == AV_SAMPLE_FMT_S16 || codec->sample_fmt ==AV_SAMPLE_FMT_S32 ||codec->sample_fmt == AV_SAMPLE_FMT_U8){

LOGE("codec->sample_fmt:%d",codec->sample_fmt);

if(*swr_ctx){

swr_free(swr_ctx);

*swr_ctx = NULL;

}

return;

}

if(*swr_ctx){

swr_free(swr_ctx);

}

*swr_ctx =swr_alloc();

if(!*swr_ctx){

LOGE("swr_alloc failed");

return;

}

/* set options*/

av_opt_set_int(*swr_ctx, "in_channel_layout", codec->channel_layout, 0);

av_opt_set_int(*swr_ctx, "in_sample_rate", codec->sample_rate, 0);

av_opt_set_sample_fmt(*swr_ctx,"in_sample_fmt", codec->sample_fmt, 0);

av_opt_set_int(*swr_ctx, "out_channel_layout", targetAudioParams->channel_layout, 0);

av_opt_set_int(*swr_ctx, "out_sample_rate", targetAudioParams->sample_rate, 0);

av_opt_set_sample_fmt(*swr_ctx, "out_sample_fmt",targetAudioParams->sample_fmt, 0);// AV_SAMPLE_FMT_S16

/* initializethe resampling context */

int ret = 0;

if ((ret =swr_init(*swr_ctx)) < 0) {

LOGE("Failed to initialize the resampling context\n");

if(*swr_ctx){

swr_free(swr_ctx);

*swr_ctx = NULL;

}

return;

}

2，转换(AV_SAMPLE_FMT_FLTPàAV_SAMPLE_FMT_S16)

int audio_swr_resampling_audio(SwrContext*swr_ctx,TargetAudioParams *targetAudioParams,AVFrame *audioFrame,uint8_t**targetData){

int len =swr_convert(swr_ctx,targetData,audioFrame->nb_samples,audioFrame->extended_data,audioFrame->nb_samples);

if(len < 0){

LOGE("error swr_convert");

goto end;

}

int dst_bufsize= len * targetAudioParams->channels *av_get_bytes_per_sample(targetAudioParams->sample_fmt);

LOGI("dst_bufsize:%d",dst_bufsize);

returndst_bufsize;

end:

return -1;

}

3，销毁

最后处理完成销毁对象

void audio_swr_resampling_audio_destory(SwrContext**swr_ctx){

if(*swr_ctx){

swr_free(swr_ctx);

*swr_ctx =NULL;

}

参考：http://stackoverflow.com/questions/14989397/how-to-convert-sample-rate-from-av-sample-fmt-fltp-to-av-sample-fmt-s16