glimbus/video.go

package main

import (
	"encoding/json"
	"fmt"
	"log/slog"
	"os/exec"
	"strconv"
	"strings"
)

// FFprobe result structures
type ProbeResult struct {
	Streams []ProbeStream `json:"streams"`
	Format  ProbeFormat   `json:"format"`
}

type ProbeStream struct {
	RFrameRate   string `json:"r_frame_rate"`
	NbFrames     string `json:"nb_frames,omitempty"`
	NbReadFrames string `json:"nb_read_frames,omitempty"`
}

type ProbeFormat struct {
	Duration string `json:"duration,omitempty"`
}

// ffprobe runs ffprobe and returns structured metadata
func ffprobe(path string) (*ProbeResult, error) {
	cmd := exec.Command("ffprobe",
		"-v", "error",
		"-print_format", "json",
		"-show_format",
		"-show_streams",
		path,
	)

	output, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("ffprobe failed: %w", err)
	}

	var result ProbeResult
	if err := json.Unmarshal(output, &result); err != nil {
		return nil, fmt.Errorf("parse ffprobe output: %w", err)
	}

	return &result, nil
}

// ffprobeFrameRate gets frame rate via direct ffprobe call (fallback)
func ffprobeFrameRate(path string) (string, error) {
	cmd := exec.Command("ffprobe",
		"-v", "error",
		"-select_streams", "v",
		"-of", "default=noprint_wrappers=1:nokey=1",
		"-show_entries", "stream=r_frame_rate",
		path,
	)

	output, err := cmd.Output()
	if err != nil {
		return "", fmt.Errorf("ffprobe frame rate failed: %w", err)
	}

	return strings.TrimSpace(string(output)), nil
}

// ffprobeFrameCountFullDecode counts frames via full decode (slow fallback)
func ffprobeFrameCountFullDecode(path string) (uint64, error) {
	cmd := exec.Command("ffprobe",
		"-v", "error",
		"-count_frames",
		"-select_streams", "v:0",
		"-show_entries", "stream=nb_read_frames",
		"-of", "default=noprint_wrappers=1:nokey=1",
		path,
	)

	output, err := cmd.Output()
	if err != nil {
		return 0, fmt.Errorf("ffprobe count frames failed: %w", err)
	}

	count, err := strconv.ParseUint(strings.TrimSpace(string(output)), 10, 64)
	if err != nil {
		return 0, fmt.Errorf("parse frame count: %w", err)
	}

	return count, nil
}

// parseFrameRate parses "num/denom" format frame rate
func parseFrameRate(s string) (float64, error) {
	parts := strings.Split(s, "/")
	if len(parts) != 2 {
		return 0, fmt.Errorf("invalid frame rate format: %s", s)
	}

	num, err := strconv.ParseFloat(parts[0], 64)
	if err != nil {
		return 0, fmt.Errorf("parse numerator: %w", err)
	}

	denom, err := strconv.ParseFloat(parts[1], 64)
	if err != nil {
		return 0, fmt.Errorf("parse denominator: %w", err)
	}

	if num == 0 && denom == 0 {
		return 0, fmt.Errorf("zero frame rate")
	}

	return num / denom, nil
}

// calculateFrameRate gets frame rate with ffprobe fallback
func calculateFrameRate(path string, frameRateStr string, firstRun bool) (float64, error) {
	frameRate, err := parseFrameRate(frameRateStr)
	if err != nil || frameRate == 0 {
		slog.Warn("got incorrect frame rate, calling ffprobe again...")

		if !firstRun {
			return 0, fmt.Errorf("couldn't get frame rate")
		}

		// Call ffprobe directly
		newFrameRateStr, err := ffprobeFrameRate(path)
		if err != nil {
			return 0, err
		}

		slog.Debug("raw ffprobe gave", "frameRate", newFrameRateStr)
		return calculateFrameRate(path, newFrameRateStr, false)
	}

	return frameRate, nil
}

// calculateFrameCount gets total frame count with fallbacks
func calculateFrameCount(path string, stream *ProbeStream, format *ProbeFormat, frameRate float64) (uint64, error) {
	// Try stream metadata first
	if stream.NbFrames != "" {
		count, err := strconv.ParseUint(stream.NbFrames, 10, 64)
		if err == nil {
			return count, nil
		}
	}

	// Try format duration
	if format.Duration != "" {
		duration, err := strconv.ParseFloat(format.Duration, 64)
		if err == nil {
			slog.Warn("fetching duration from format metadata...")
			return uint64(duration * frameRate), nil
		}
	}

	// Fallback to full decode
	slog.Warn("file didn't provide frame metadata, calculating it ourselves...")
	return ffprobeFrameCountFullDecode(path)
}

// extractFrame extracts a single frame at the given index using ffmpeg
func extractFrame(inputPath, outputPath string, frameIndex int, frameRate float64) error {
	// Calculate timeline position
	timelineIndex := float64(frameIndex) / frameRate
	timelineStr := fmt.Sprintf("%.5f", timelineIndex)

	slog.Debug("construct command", "timelineIndex", timelineIndex, "timelineStr", timelineStr)
	slog.Info("ffmpeg command", "args", fmt.Sprintf("-nostdin -y -ss %s -i %s -vframes 1 %s", timelineStr, inputPath, outputPath))

	// Use fast seeking with -ss before -i
	cmd := exec.Command("ffmpeg",
		"-nostdin",
		"-y",
		"-ss", timelineStr,
		"-i", inputPath,
		"-vframes", "1",
		outputPath,
	)

	output, err := cmd.CombinedOutput()
	if err != nil {
		slog.Error("ffmpeg failed", "output", string(output), "error", err)
		return fmt.Errorf("ffmpeg failed: %w", err)
	}

	slog.Debug("ffmpeg output", "output", string(output))
	return nil
}

// getFrameSkipSeconds returns the frame sampling interval based on video duration
func getFrameSkipSeconds(totalSeconds int) int {
	switch {
	case totalSeconds <= 10:
		return 1
	case totalSeconds <= 60:
		return 5
	case totalSeconds <= 120:
		return 7
	case totalSeconds <= 300:
		return 10
	case totalSeconds <= 1000:
		return 15
	case totalSeconds <= 1200:
		return 20
	default:
		return 26
	}
}