datarhei-dragonfork-core/app/webrtc/ffmpeg_args.go

package webrtc

import (
	"fmt"

	appcfg "github.com/datarhei/core/v16/restream/app"
)

// BuildArgs emits the FFmpeg output-leg args for the WebRTC side of a
// process. It produces two separate "outputs" — one for video on
// videoPort, one for audio on videoPort+1. Each output ends with its
// UDP address so the slice is structured for consumption by
// restream.AppendOutput after splitting on the track boundary.
//
// Copy vs. re-encode: if ForceTranscode is false, we assume the upstream
// source is already H.264 + Opus and pass them through (copy). When the
// source doesn't match, FFmpeg will fail at runtime and the process will
// restart — the user can flip ForceTranscode on to get a baseline-profile
// H.264 + Opus re-encode.
func BuildArgs(cfg appcfg.ConfigWebRTC, videoPort int) []string {
	vcopy := []string{"-c:v", "copy"}
	acopy := []string{"-c:a", "copy"}
	if cfg.ForceTranscode {
		vcopy = []string{
			"-c:v", "libx264",
			"-preset", "veryfast",
			"-profile:v", "baseline",
			"-pix_fmt", "yuv420p",
			"-tune", "zerolatency",
			"-g", "60",
		}
		acopy = []string{"-c:a", "libopus", "-b:a", "96k"}
	}

	videoMap := cfg.VideoMap
	if videoMap == "" {
		videoMap = "0:v:0"
	}
	audioMap := cfg.AudioMap
	if audioMap == "" {
		audioMap = "0:a:0"
	}

	args := []string{"-map", videoMap}
	args = append(args, vcopy...)
	args = append(args,
		"-payload_type", fmt.Sprint(cfg.VideoPT),
		"-f", "rtp",
		fmt.Sprintf("udp://127.0.0.1:%d?pkt_size=1316", videoPort),
	)

	args = append(args, "-map", audioMap)
	args = append(args, acopy...)
	args = append(args,
		"-payload_type", fmt.Sprint(cfg.AudioPT),
		"-f", "rtp",
		fmt.Sprintf("udp://127.0.0.1:%d?pkt_size=1316", videoPort+1),
	)

	return args
}