FFmpeg Implementing Audio Resample (resampling)

FFmpeg Implementing Audio Resample (resampling)

The following code is an implementation of the three main elements of audio: Channel, sample, sample rate change demo such as two channels into mono, 44100->48000,float->s16 and so on.

int AudioResampling (AVCodecContext * audio_dec_ctx, AVFrame * pAudioDecodeFrame,
int out_sample_fmt, int out_channels, int out_sample_rate, uint8_t * out_buf)
{
///////////////////////////////////////////////////////// /////////////////////////
SwrContext * swr_ctx = NULL;
int data_size = 0;
int ret = 0;
int64_t src_ch_layout = AV_CH_LAYOUT_STEREO; // Initialize this to adjust according to different files
int64_t dst_ch_layout = AV_CH_LAYOUT_STEREO; // Set ok here
int dst_nb_channels = 0;
int dst_linesize = 0;
int src_nb_samples = 0;
int dst_nb_samples = 0;
int max_dst_nb_samples = 0;
uint8_t ** dst_data = NULL;
int resampled_data_size = 0;
Ranch
// Resample
if (swr_ctx)
{
swr_free (& swr_ctx);
}
swr_ctx = swr_alloc ();
if (! swr_ctx)
{
printf ("swr_alloc error \ n");
return -1;
}

src_ch_layout = (audio_dec_ctx-> channel_layout &&
audio_dec_ctx-> channels ==
av_get_channel_layout_nb_channels (audio_dec_ctx-> channel_layout))?
audio_dec_ctx-> channel_layout:
av_get_default_channel_layout (audio_dec_ctx-> channels);

if (out_channels == 1)
{
dst_ch_layout = AV_CH_LAYOUT_MONO;
}
else if (out_channels == 2)
{
dst_ch_layout = AV_CH_LAYOUT_STEREO;
}
else
{
		//Scalable
}

if (src_ch_layout <= 0)
{
printf ("src_ch_layout error \ n");
return -1;
}

src_nb_samples = pAudioDecodeFrame-> nb_samples;
if (src_nb_samples <= 0)
{
printf ("src_nb_samples error \ n");
return -1;
}

/ * set options * /
av_opt_set_int (swr_ctx, "in_channel_layout", src_ch_layout, 0);
av_opt_set_int (swr_ctx, "in_sample_rate", audio_dec_ctx-> sample_rate, 0);
av_opt_set_sample_fmt (swr_ctx, "in_sample_fmt", audio_dec_ctx-> sample_fmt, 0);

av_opt_set_int (swr_ctx, "out_channel_layout", dst_ch_layout, 0);
av_opt_set_int (swr_ctx, "out_sample_rate", out_sample_rate, 0);
av_opt_set_sample_fmt (swr_ctx, "out_sample_fmt", (AVSampleFormat) out_sample_fmt, 0);
swr_init (swr_ctx);

max_dst_nb_samples = dst_nb_samples =
av_rescale_rnd (src_nb_samples, out_sample_rate, audio_dec_ctx-> sample_rate, AV_ROUND_UP);
if (max_dst_nb_samples <= 0)
{
printf ("av_rescale_rnd error \ n");
return -1;
}

dst_nb_channels = av_get_channel_layout_nb_channels (dst_ch_layout);
ret = av_samples_alloc_array_and_samples (& dst_data, & dst_linesize, dst_nb_channels,
dst_nb_samples, (AVSampleFormat) out_sample_fmt, 0);
if (ret <0)
{
printf ("av_samples_alloc_array_and_samples error \ n");
return -1;
}


dst_nb_samples = av_rescale_rnd (swr_get_delay (swr_ctx, audio_dec_ctx-> sample_rate) +
src_nb_samples, out_sample_rate, audio_dec_ctx-> sample_rate, AV_ROUND_UP);
if (dst_nb_samples <= 0)
{
printf ("av_rescale_rnd error \ n");
return -1;
}
if (dst_nb_samples> max_dst_nb_samples)
{
av_free (dst_data [0]);
ret = av_samples_alloc (dst_data, & dst_linesize, dst_nb_channels,
dst_nb_samples, (AVSampleFormat) out_sample_fmt, 1);
max_dst_nb_samples = dst_nb_samples;
}

data_size = av_samples_get_buffer_size (NULL, audio_dec_ctx-> channels,
pAudioDecodeFrame-> nb_samples,
audio_dec_ctx-> sample_fmt, 1);
if (data_size <= 0)
{
printf ("av_samples_get_buffer_size error \ n");
return -1;
}
resampled_data_size = data_size;
Ranch
if (swr_ctx)
{
ret = swr_convert (swr_ctx, dst_data, dst_nb_samples,
(const uint8_t **) pAudioDecodeFrame-> data, pAudioDecodeFrame-> nb_samples);
if (ret <= 0)
{
printf ("swr_convert error \ n");
return -1;
}

resampled_data_size = av_samples_get_buffer_size (& dst_linesize, dst_nb_channels,
ret, (AVSampleFormat) out_sample_fmt, 1);
if (resampled_data_size <= 0)
{
printf ("av_samples_get_buffer_size error \ n");
return -1;
}
}
else
{
printf ("swr_ctx null error \ n");
return -1;
}

// Return the value
memcpy (out_buf, dst_data [0], resampled_data_size);

if (dst_data)
{
av_freep (& dst_data [0]);
}
av_freep (& dst_data);
dst_data = NULL;

if (swr_ctx)
{
swr_free (& swr_ctx);
}
return resampled_data_size;
}

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