FFMPEG encode audio

 

#include 
#include 
#include 


extern "C"
{
#include 

#include 
#include 
#include 
#include 
}

/* check that a given sample format is supported by the encoder */
static int check_sample_fmt(const AVCodec *codec, enum AVSampleFormat sample_fmt)
{
	const enum AVSampleFormat *p = codec->sample_fmts;

	while (*p != AV_SAMPLE_FMT_NONE) {
		if (*p == sample_fmt)
			return 1;
		p++;
	}
	return 0;
}

/* just pick the highest supported samplerate */
static int select_sample_rate(const AVCodec *codec)
{
	const int *p;
	int best_samplerate = 0;

	if (!codec->supported_samplerates)
		return 44100;

	p = codec->supported_samplerates;
	while (*p) {
		if (!best_samplerate || abs(44100 - *p) < abs(44100 - best_samplerate))
			best_samplerate = *p;
		p++;
	}
	return best_samplerate;
}

/* select layout with the highest channel count */
static int select_channel_layout(const AVCodec *codec)
{
	const uint64_t *p;
	uint64_t best_ch_layout = 0;
	int best_nb_channels = 0;

	if (!codec->channel_layouts)
		return AV_CH_LAYOUT_STEREO;

	p = codec->channel_layouts;
	while (*p) {
		int nb_channels = av_get_channel_layout_nb_channels(*p);

		if (nb_channels > best_nb_channels) {
			best_ch_layout = *p;
			best_nb_channels = nb_channels;
		}
		p++;
	}
	return best_ch_layout;
}

int main(int argc, char **argv)
{

	AVPacket pkt;
	int i, j, k, ret, got_output;
	
	uint16_t *samples;

	if (argc <= 1) {
		fprintf(stderr, "Usage: %s 
\n", argv[0]);
		return 0;
	}
	const char *filename = "./beijingbeijing_8k_16bits_memo.pcm";

	/* register all the codecs */
	avcodec_register_all();

	/* find the MP2 encoder */
	const AVCodec *codec = avcodec_find_encoder(AV_CODEC_ID_MP2);
	if (!codec) {
		fprintf(stderr, "Codec not found\n");
		exit(1);
	}

	AVCodecContext *c = avcodec_alloc_context3(codec);
	if (!c) {
		fprintf(stderr, "Could not allocate audio codec context\n");
		exit(1);
	}

	/* put sample parameters */
	c->bit_rate = 64000;

	/* check that the encoder supports s16 pcm input */
	c->sample_fmt = AV_SAMPLE_FMT_S16;
	if (!check_sample_fmt(codec, c->sample_fmt)) {
		fprintf(stderr, "Encoder does not support sample format %s",
			av_get_sample_fmt_name(c->sample_fmt));
		exit(1);
	}

	/* select other audio parameters supported by the encoder */
	c->sample_rate = select_sample_rate(codec);
	c->channel_layout = select_channel_layout(codec);
	c->channels = av_get_channel_layout_nb_channels(c->channel_layout);

	/* open it */
	if (avcodec_open2(c, codec, NULL) < 0) {
		fprintf(stderr, "Could not open codec\n");
		exit(1);
	}

	FILE *f = fopen(filename, "wb");
	if (!f) {
		fprintf(stderr, "Could not open %s\n", filename);
		exit(1);
	}

	/* frame containing input raw audio */
	AVFrame *frame = av_frame_alloc();
	if (!frame) {
		fprintf(stderr, "Could not allocate audio frame\n");
		exit(1);
	}

	frame->nb_samples = c->frame_size;
	frame->format = c->sample_fmt;
	frame->channel_layout = c->channel_layout;

	/* allocate the data buffers */
	ret = av_frame_get_buffer(frame, 0);
	if (ret < 0) {
		fprintf(stderr, "Could not allocate audio data buffers\n");
		exit(1);
	}

	/* encode a single tone sound */
	float t = 0;
	float tincr = 2 * M_PI * 440.0 / c->sample_rate;
	for (i = 0; i < 200; i++) {
		av_init_packet(&pkt);
		pkt.data = NULL; // packet data will be allocated by the encoder
		pkt.size = 0;

		/* make sure the frame is writable -- makes a copy if the encoder
		* kept a reference internally */
		ret = av_frame_make_writable(frame);
		if (ret < 0)
			exit(1);
		samples = (uint16_t*)frame->data[0];

		for (j = 0; j < c->frame_size; j++) {
			samples[2 * j] = (int)(sin(t) * 10000);

			for (k = 1; k < c->channels; k++)
				samples[2 * j + k] = samples[2 * j];
			t += tincr;
		}
		/* encode the samples */
		ret = avcodec_encode_audio2(c, &pkt, frame, &got_output);
		if (ret < 0) {
			fprintf(stderr, "Error encoding audio frame\n");
			exit(1);
		}
		if (got_output) {
			fwrite(pkt.data, 1, pkt.size, f);
			av_packet_unref(&pkt);
		}
	}

	/* get the delayed frames */
	for (got_output = 1; got_output; i++) {
		ret = avcodec_encode_audio2(c, &pkt, NULL, &got_output);
		if (ret < 0) {
			fprintf(stderr, "Error encoding frame\n");
			exit(1);
		}

		if (got_output) {
			fwrite(pkt.data, 1, pkt.size, f);
			av_packet_unref(&pkt);
		}
	}
	fclose(f);

	av_frame_free(&frame);
	avcodec_free_context(&c);

	return 0;
}