ffmini/ffmini.cpp

#include <iostream>
#include <filesystem>

#include "fmt/format.h"
#include "miniaudio.h"

extern "C" {
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavcodec/avcodec.h"
}

struct ffmini {
    AVFormatContext* format_context;
    AVCodecContext* codec_context;
    std::int64_t stream_index = -1;
    char const* path = "C:/Users/miku/Downloads/Porter Robinson - Trying to Feel Alive (Official Audio).webm";
    std::string filename{};
    AVStream* stream = nullptr;
    AVPacket *pkt = nullptr;
    AVFrame* frame = nullptr;

    std::size_t byte_read = 0;

    ffmini() {
        format_context = avformat_alloc_context();
        if (!format_context)
            throw std::runtime_error("Failed to create AVFormatContext");

        if (avformat_open_input(&format_context, path, nullptr, nullptr) != 0)
            throw std::runtime_error(fmt::format("Failed to open file {}\n", filename));

        if (avformat_find_stream_info(format_context, nullptr) < 0)
            throw std::runtime_error("Error loading stream info");

        AVCodec const* codec = nullptr;
        for (std::uint32_t i = 0; i < format_context->nb_streams; ++i) {
            auto* params = format_context->streams[i]->codecpar;
            codec = avcodec_find_decoder(params->codec_id);
            if (!codec) continue;
            if (params->codec_type == AVMEDIA_TYPE_AUDIO) {
                stream_index = static_cast<std::int64_t>(i);
            }
        }

        if (stream_index == -1)
            throw std::runtime_error(fmt::format("Couldn't find valid audio track inside file: {}", filename));

        codec_context = avcodec_alloc_context3(codec);
        if (!codec_context)
            throw std::runtime_error("Couldn't create AVCodecContext");

        auto* codec_params = format_context->streams[stream_index]->codecpar;
        if (avcodec_parameters_to_context(codec_context, codec_params) < 0)
            throw std::runtime_error("Couldn't initialize AVCodecContext");

        if (avcodec_open2(codec_context, codec, nullptr) < 0)
            throw std::runtime_error("Couln't open codec");
        stream = format_context->streams[stream_index];

        frame = av_frame_alloc();
        if (!frame)
            throw std::runtime_error("Couldn't allocate AVFrame");

        pkt = av_packet_alloc();
        if (!pkt)
            throw std::runtime_error("Couldn't allocate AVPacket");

        std::filesystem::path file{path};
        filename = file.filename().string();

        // char buffer[256]{};
        // av_get_channel_layout_string(buffer, 256, codec_params->channels, codec_params->channel_layout);

        fmt::print("File: {}\n", filename);
        fmt::print("Sample rate: {}\n", codec_params->sample_rate);
        fmt::print("Channels: {}\n", codec_params->channels);
    }
    ~ffmini() {
        avcodec_free_context(&codec_context);
        avformat_close_input(&format_context);
        avformat_free_context(format_context);
        av_frame_free(&frame);
        av_packet_free(&pkt);
    }

    auto decode() -> void {
        if (byte_read != 0) return;

        static auto make_error = [](int err) {
            static char str[AV_ERROR_MAX_STRING_SIZE]{};
            return av_make_error_string(str, AV_ERROR_MAX_STRING_SIZE, err);
        };

        int ret = 0;
        while (av_read_frame(format_context, pkt) >= 0) {
            if (pkt->stream_index != stream_index) {
                av_packet_unref(pkt);
                continue;
            }
            ret = avcodec_send_packet(codec_context, pkt);
            if (ret < 0) {
                fmt::print(stderr, "Error submitting the packet to the decoder!\n");
                return;
            }

            ret = avcodec_receive_frame(codec_context, frame);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                av_packet_unref(pkt);
                fmt::print("error\n");
                continue;
            } else if (ret < 0) {
                fmt::print(stderr, "Failed to decode packet: %s\n", make_error(ret));
                break;
            }

            av_packet_unref(pkt);
            break;
        }

        auto const data_size = av_get_bytes_per_sample(codec_context->sample_fmt);
        if (data_size < 0) {
            fmt::print(stderr, "Failed to calculate data size\n");
        }
    }
};

auto callback([[maybe_unused]]ma_device* device, [[maybe_unused]]void* output, [[maybe_unused]]void const* input, [[maybe_unused]]ma_uint32 frame_count) -> void {
    auto* ptr = static_cast<ffmini*>(device->pUserData);
    ptr->decode();
    auto& start = ptr->byte_read;
    auto* frame = ptr->frame;
    auto* codec = ptr->codec_context;

    std::size_t read = 0;
    auto const data_size = av_get_bytes_per_sample(codec->sample_fmt);
    if (data_size < 0) {
        fmt::print(stderr, "Failed to calculate data size\n");
    }

    auto* dst = static_cast<float*>(output);
    for (int i = start; i < frame->nb_samples; i++) {
        for (int ch = 0; ch < codec->channels; ch++) {
            std::memcpy(dst++, frame->data[ch] + data_size * i, data_size);
        }
        ++read;
        if (read >= frame_count) break;
    }

    start = start + read;
    if (int(start) >= frame->nb_samples) start = 0;
}

auto main([[maybe_unused]]int argc, [[maybe_unused]]char const* argv[]) -> int {
    ffmini decoder{};

    ma_device device;
    auto device_config = ma_device_config_init(ma_device_type_playback);
    device_config.playback.format   = ma_format_f32;
    device_config.playback.channels = 2;
    device_config.sampleRate        = decoder.stream->codecpar->sample_rate;
    device_config.dataCallback      = callback;
    device_config.pUserData         = &decoder;

    if (ma_device_init(nullptr, &device_config, &device) != MA_SUCCESS) {
        fmt::print(stderr, "Failed to open playback device\n");
        return 1;
    }

    if (ma_device_start(&device) != MA_SUCCESS) {
        fmt::print(stderr, "Failed to start playback device.\n");
        return 1;
    }

    fmt::print("Now playing: {}\n", decoder.filename);
    fmt::print("Press enter to quit...");
    std::cin.get();

    ma_device_uninit(&device);
    return 0;
}