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/* Read decoded audio samples from stdin and send them to ALSA using ffmpeg.
* Input format:
* - two channels (front left, front right)
* - samples in interleaved format (L R L R ...)
* - samples are little-endian 32-bit floats
* - sample rate is 44100
*
* Usage:
* ./ffmpeg_play < cool_song_samples
*/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
extern "C" {
#include <libavformat/avformat.h>
#include <libavdevice/avdevice.h>
#include <libavcodec/avcodec.h>
}
int main(int argc, char** argv) {
if (argc != 1) {
fprintf(stderr, "usage: %s < input_file\n", argv[0]);
exit(1);
}
const int in_channels = 2, in_samples = 512, sample_rate = 44100;
const int bitrate = 64000;
const int max_buffer_size =
av_samples_get_buffer_size(
NULL, in_channels, in_samples, AV_SAMPLE_FMT_FLT, 1);
// register supported formats and codecs
av_register_all();
// register supported devices
avdevice_register_all();
// find output format for ALSA device
AVOutputFormat* fmt = av_guess_format("alsa", NULL, NULL);
if (!fmt) {
fprintf(stderr, "av_guess_format()\n");
exit(1);
}
// allocate empty format context
// provides methods for writing output packets
AVFormatContext* fmt_ctx = avformat_alloc_context();
if (!fmt_ctx) {
fprintf(stderr, "avformat_alloc_context()\n");
exit(1);
}
// tell format context to use ALSA as ouput device
fmt_ctx->oformat = fmt;
// add stream to format context
AVStream* stream = avformat_new_stream(fmt_ctx, NULL);
if (!stream) {
fprintf(stderr, "avformat_new_stream()\n");
exit(1);
}
// initialize stream codec context
// format conetxt uses codec context when writing packets
AVCodecContext* codec_ctx = stream->codec;
assert(codec_ctx);
codec_ctx->codec_id = CODEC_ID_PCM_F32LE;
codec_ctx->codec_type = AVMEDIA_TYPE_AUDIO;
codec_ctx->sample_fmt = AV_SAMPLE_FMT_FLT;
codec_ctx->bit_rate = bitrate;
codec_ctx->sample_rate = sample_rate;
codec_ctx->channels = in_channels;
codec_ctx->channel_layout = AV_CH_FRONT_LEFT | AV_CH_FRONT_RIGHT;
// allocate buffer for input samples
uint8_t* buffer = (uint8_t*)av_malloc(max_buffer_size);
assert(buffer);
// initialze output device
if (avformat_write_header(fmt_ctx, NULL) < 0) {
fprintf(stderr, "avformat_write_header()\n");
exit(1);
}
for (;;) {
memset(buffer, 0, max_buffer_size);
// read input buffer from stdin
ssize_t ret = read(STDIN_FILENO, buffer, max_buffer_size);
if (ret < 0) {
fprintf(stderr, "read(stdin)\n");
exit(1);
}
if (ret == 0) {
break;
}
// create output packet
AVPacket packet;
av_init_packet(&packet);
packet.data = buffer;
packet.size = max_buffer_size;
// write output packet to format context
if (av_write_frame(fmt_ctx, &packet) < 0) {
fprintf(stderr, "av_write_frame()\n");
exit(1);
}
}
av_free(buffer);
avformat_free_context(fmt_ctx);
return 0;
}