To eliminate XY problem, here is what's my situation. I have source YouTube videos in MP4 container. I create voiceovers for them using Sony Vegas on Windows machine and then export them as WAV file, which I then use as new audio track for original video with ffmpeg. If I want to translate on-screen captions (e.g. public service announcements, signs, intro titles or anything like that), then Sony Vegas transcoding goes like forever and creates enormous files. And my kind of solution for this would be to split original video into pieces and only transcode the altered part, and then just concatenate them:
unaltered-start.mp4 + altered.mp4 + unaltered-end.mp4
using intermediate files method in Concat protocol
So my question here is how can I convert
altered.mp4 into exact same format as
unaltered-start.mp4 (resolution, encoding, bitrate, etc.)? Is there any ffmpeg flag to use in the meaning "use encoding format exactly from this media file"?