// Key fixes applied:
// 1. isInterlacedSource check: for progressive deltacast signals, skip yadif deinterlacer and use split only
//    - Before: yadif=mode=1:deint=1 on progressive input doubled framerate (59.94->119.88 fps)
//    - After: progressive signals use '[0:v]split=2[vhi][vlo]' without yadif
// 2. currentFps calculated from framesReceived / elapsedSec instead of ffmpeg's running average
//    - Before: used ffmpeg stderr fps= which is encoding speed average (starts at ~28fps)
//    - After: calculates actual capture rate from wall-clock time
// 3. recordingStartedAt timestamp set when recording starts, cleared when stopping