#include <iostream>
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#include <vector>
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#include <cstring>
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#include <fstream>
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extern "C" {
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#include <libavutil/opt.h>
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#include <libavcodec/avcodec.h>
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#include <libavformat/avformat.h>
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#include <libavutil/channel_layout.h>
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#include <libavutil/samplefmt.h>
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#include <libswresample/swresample.h>
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}
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int main(int argc, char* argv[]) {
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// from buff
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FILE* fp;
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fp = fopen(argv[1], "rb");
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if (fp == nullptr)
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{
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return -1;
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}
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fseek(fp, 0, SEEK_END);
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uint32_t n_file_len = ftell(fp);
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fseek(fp, 0, SEEK_SET);
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char* buf = (char *)malloc(n_file_len);
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memset(buf, 0, n_file_len);
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fread(buf, 1, n_file_len, fp);
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fclose(fp);
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AVIOContext* avio_ctx = avio_alloc_context(
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(unsigned char*)buf, // buffer
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n_file_len, // buffer size
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0, // write flag (0 for read-only)
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nullptr, // opaque pointer (not used here)
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nullptr, // read callback (not used here)
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nullptr, // write callback (not used here)
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nullptr // seek callback (not used here)
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);
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AVFormatContext* formatContext = avformat_alloc_context();
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formatContext->pb = avio_ctx;
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if (avformat_open_input(&formatContext, "", NULL, NULL) != 0) {
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printf("Error: Could not open input file.");
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avformat_close_input(&formatContext);
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avformat_free_context(formatContext);
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return -1;
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}
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// from file
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// AVFormatContext* formatContext = avformat_alloc_context();
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// if (avformat_open_input(&formatContext, argv[1], NULL, NULL) != 0) {
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// printf("Error: Could not open input file.");
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// avformat_close_input(&formatContext);
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// avformat_free_context(formatContext);
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// return -1;
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// }
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if (avformat_find_stream_info(formatContext, NULL) < 0) {
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printf("Error: Could not find stream information.");
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avformat_close_input(&formatContext);
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avformat_free_context(formatContext);
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return -1;
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}
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const AVCodec* codec = NULL;
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AVCodecParameters* codecParameters = NULL;
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int audioStreamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_AUDIO, -1, -1, &codec, 0);
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if (audioStreamIndex >= 0) {
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codecParameters = formatContext->streams[audioStreamIndex]->codecpar;
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}
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AVCodecContext* codecContext = avcodec_alloc_context3(codec);
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if (!codecContext) {
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fprintf(stderr, "Failed to allocate codec context\n");
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avformat_close_input(&formatContext);
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return -1;
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}
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if (avcodec_parameters_to_context(codecContext, codecParameters) != 0) {
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printf("Error: Could not copy codec parameters to codec context.");
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avcodec_free_context(&codecContext);
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avformat_close_input(&formatContext);
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avformat_free_context(formatContext);
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return -1;
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}
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if (avcodec_open2(codecContext, codec, NULL) < 0) {
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printf("Error: Could not open audio decoder.");
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avcodec_free_context(&codecContext);
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avformat_close_input(&formatContext);
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avformat_free_context(formatContext);
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return -1;
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}
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SwrContext *swr_ctx = swr_alloc_set_opts(
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nullptr, // allocate a new context
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AV_CH_LAYOUT_MONO, // output channel layout (stereo)
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AV_SAMPLE_FMT_S16, // output sample format (signed 16-bit)
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16000, // output sample rate (same as input)
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av_get_default_channel_layout(codecContext->channels), // input channel layout
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codecContext->sample_fmt, // input sample format
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codecContext->sample_rate, // input sample rate
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0, // logging level
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nullptr // parent context
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);
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if (swr_ctx == nullptr) {
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std::cerr << "Could not initialize resampler" << std::endl;
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avcodec_free_context(&codecContext);
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avformat_close_input(&formatContext);
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avformat_free_context(formatContext);
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return -1;
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}
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if (swr_init(swr_ctx) != 0) {
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std::cerr << "Could not initialize resampler" << std::endl;
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swr_free(&swr_ctx);
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avcodec_free_context(&codecContext);
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avformat_close_input(&formatContext);
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avformat_free_context(formatContext);
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return -1;
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}
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// to pcm
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FILE *out_file = fopen("output.pcm", "wb");
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AVPacket* packet = av_packet_alloc();
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AVFrame* frame = av_frame_alloc();
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std::vector<uint8_t> resampled_buffer;
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while (av_read_frame(formatContext, packet) >= 0) {
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if (packet->stream_index == audioStreamIndex) {
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if (avcodec_send_packet(codecContext, packet) >= 0) {
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while (avcodec_receive_frame(codecContext, frame) >= 0) {
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// Resample audio if necessary
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int in_samples = frame->nb_samples;
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uint8_t **in_data = frame->extended_data;
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int out_samples = av_rescale_rnd(in_samples,
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16000,
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codecContext->sample_rate,
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AV_ROUND_DOWN);
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int resampled_size = out_samples * av_get_bytes_per_sample(AV_SAMPLE_FMT_S16);
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if (resampled_buffer.size() < resampled_size) {
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resampled_buffer.resize(resampled_size);
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}
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uint8_t *resampled_data = resampled_buffer.data();
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int ret = swr_convert(
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swr_ctx,
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&resampled_data, // output buffer
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resampled_size, // output buffer size
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(const uint8_t **)(frame->data), //(const uint8_t **)(frame->extended_data)
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in_samples // input buffer size
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);
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if (ret < 0) {
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std::cerr << "Error resampling audio" << std::endl;
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break;
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}
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fwrite(resampled_buffer.data(), sizeof(int8_t), resampled_size, out_file);
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}
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}
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}
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av_packet_unref(packet);
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}
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fclose(out_file);
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avio_context_free(&avio_ctx);
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avformat_close_input(&formatContext);
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avformat_free_context(formatContext);
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avcodec_free_context(&codecContext);
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swr_free(&swr_ctx);
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av_packet_free(&packet);
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av_frame_free(&frame);
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}
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