dmf-studio-rnd/shared/FlowDef.hpp

#pragma once
#include <fstream>
#include <string>
#include <nlohmann/json.hpp>

namespace dmf {

// Generates a minimal but valid NMOS IS-04 flow definition JSON string
// for a video/v210 flow. MXL uses this to set up the ring buffer geometry.
inline std::string make_video_flow_def(
    const std::string& flow_id,
    const std::string& label,
    int width, int height,
    int fps_num, int fps_den = 1)
{
    using json = nlohmann::json;
    return json{
        {"id",             flow_id},
        {"format",         "urn:x-nmos:format:video"},
        {"label",          label},
        {"description",    label + " MXL Video Flow"},
        {"media_type",     "video/v210"},
        {"parents",        json::array()},
        {"grain_rate",     {{"numerator", fps_num}, {"denominator", fps_den}}},
        {"frame_width",    width},
        {"frame_height",   height},
        {"interlace_mode", "progressive"},
        {"colorspace",     "BT709"},
        {"tags", {
            {"urn:x-nmos:tag:grouphint/v1.0", json::array({label + ":Video"})}
        }},
        {"components", json::array({
            {{"name","Y"},  {"width",width},   {"height",height}, {"bit_depth",10}},
            {{"name","Cb"}, {"width",width/2}, {"height",height}, {"bit_depth",10}},
            {{"name","Cr"}, {"width",width/2}, {"height",height}, {"bit_depth",10}}
        })}
    }.dump();
}

// Generates a minimal but valid NMOS IS-04 flow definition JSON string
// for a raw PCM audio flow. grain_rate_num/den sets the grain delivery rate
// (default 25/1 = one grain per video frame). MXL computes grain size as
// sample_rate / grain_rate samples per grain.
inline std::string make_audio_flow_def(
    const std::string& flow_id,
    const std::string& label,
    int sample_rate,
    int channels,
    int bit_depth       = 32,
    int grain_rate_num  = 25,
    int grain_rate_den  = 1)
{
    using json = nlohmann::json;
    static const char* ch_labels[] = {"L","R","C","LFE","Ls","Rs","Lss","Rss"};
    json ch_arr = json::array();
    for (int i = 0; i < channels; ++i)
        ch_arr.push_back({{"label", i < 8 ? ch_labels[i] : ("Ch" + std::to_string(i + 1))}});
    return json{
        {"id",          flow_id},
        {"format",      "urn:x-nmos:format:audio"},
        {"label",       label},
        {"description", label + " MXL Audio Flow"},
        {"media_type",  bit_depth == 32 ? "audio/float32" : "audio/L" + std::to_string(bit_depth)},
        {"parents",     json::array()},
        {"grain_rate",  {{"numerator", grain_rate_num}, {"denominator", grain_rate_den}}},
        {"sample_rate", {{"numerator", sample_rate},    {"denominator", 1}}},
        {"channels",       ch_arr},   // NMOS IS-04 metadata (ignored by MXL)
        {"channel_count",  channels},  // MXL uses this for grain buffer geometry
        {"bit_depth",      bit_depth}, // must be 32 or 64
        {"tags", {
            {"urn:x-nmos:tag:grouphint/v1.0", json::array({label + ":Audio"})}
        }},
    }.dump();
}

// Actual video format as written into the MXL flow_def.json by a source node.
// Sink nodes use this to read width/height/fps from MXL instead of trusting config values.
struct VideoFlowInfo {
    int width   = 1920;
    int height  = 1080;
    int fps_num = 25;
    int fps_den = 1;
};

inline VideoFlowInfo read_video_flow_info(const std::string& domain, const std::string& flow_id) {
    VideoFlowInfo info;
    const std::string path = domain + "/" + flow_id + ".mxl-flow/flow_def.json";
    std::ifstream f(path);
    if (!f.is_open()) return info;
    const auto j = nlohmann::json::parse(f, nullptr, /*allow_exceptions=*/false);
    if (j.is_discarded()) return info;
    info.width   = j.value("frame_width",  1920);
    info.height  = j.value("frame_height", 1080);
    if (j.contains("grain_rate")) {
        info.fps_num = j["grain_rate"].value("numerator",   25);
        info.fps_den = j["grain_rate"].value("denominator",  1);
    }
    return info;
}

// Actual audio format as written into the MXL flow_def.json by a source node.
struct AudioFlowInfo {
    int sample_rate      = 48000;
    int channels         = 2;
    int samples_per_grain = 1920; // sample_rate * grain_rate_den / grain_rate_num
};

inline AudioFlowInfo read_audio_flow_info(const std::string& domain, const std::string& flow_id) {
    AudioFlowInfo info;
    const std::string path = domain + "/" + flow_id + ".mxl-flow/flow_def.json";
    std::ifstream f(path);
    if (!f.is_open()) return info;
    const auto j = nlohmann::json::parse(f, nullptr, /*allow_exceptions=*/false);
    if (j.is_discarded()) return info;
    if (j.contains("sample_rate"))
        info.sample_rate = j["sample_rate"].value("numerator", 48000);
    info.channels = j.value("channel_count", 2);
    if (j.contains("grain_rate") && info.sample_rate > 0) {
        const int gr_num = j["grain_rate"].value("numerator",   25);
        const int gr_den = j["grain_rate"].value("denominator",  1);
        if (gr_num > 0)
            info.samples_per_grain = info.sample_rate * gr_den / gr_num;
    }
    return info;
}

} // namespace dmf