This script modifies the timecode of videos filmed with Sony cameras (it may work on others), so that the time between the clips is accurately represented. It only has 2-second accuracy (since it's based on the time of start of recording, which only has a second accuracy), but this is enough to make a rough sync for clips. It was only tested on …

modify-timecode.sh

#!/usr/bin/env bash
# ---------------------------------------------------------------------------
#  modify-timecode.sh
#  ---------------------------------------------------------------------------
#  • First clip  -> 00:00:00:00
#  • Others      -> offset from first clip’s “Encoded date”
#  • Frames part -> always 00
#  • Streams are copied, NO re-encoding
#
#  Needs: mediainfo, ffmpeg   (brew install mediainfo ffmpeg)
# ---------------------------------------------------------------------------

set -euo pipefail
IFS=$'\n'            # keep filenames with blanks intact

# ---------------------------------------------------------------------------
# 1. Collect *.mp4 (case-insensitive) in the current directory
# ---------------------------------------------------------------------------
shopt -s nocaseglob nullglob
files=( *.mp4 )
shopt -u nocaseglob

if [ ${#files[@]} -eq 0 ]; then
    echo "No MP4 files found – aborting." >&2
    exit 1
fi

# ---------------------------------------------------------------------------
# 2. First pass – find the earliest Encoded_Date  (=> reference 0 s)
# ---------------------------------------------------------------------------
first_epoch=''
for f in "${files[@]}"; do
    enc_date=$(mediainfo --Output='General;%Encoded_Date%' -- "$f") || {
        echo "Cannot read Encoded_Date from '$f' – skipping." >&2
        continue
    }
    # expected format: “UTC 2024-06-19 13:59:57”
    enc_date=${enc_date#UTC }          # strip leading “UTC ”
    if ep=$(date -u -j -f "%Y-%m-%d %H:%M:%S" "$enc_date" "+%s" 2>/dev/null)
    then
        if [ -z "$first_epoch" ] || [ "$ep" -lt "$first_epoch" ]; then
            first_epoch=$ep
        fi
    else
        echo "Cannot parse date '$enc_date' in '$f' – skipping." >&2
    fi
done

if [ -z "$first_epoch" ]; then
    echo "No usable Encoded_Date values – aborting." >&2
    exit 1
fi

echo "Earliest clip time: $(date -u -r "$first_epoch" "+%Y-%m-%d %H:%M:%S") (t = 0)"

# ---------------------------------------------------------------------------
# 3. Second pass – compute offset for every file and inject time-code
# ---------------------------------------------------------------------------
for f in "${files[@]}"; do
    enc_date=$(mediainfo --Output='General;%Encoded_Date%' -- "$f") || continue
    enc_date=${enc_date#UTC }
    ep=$(date -u -j -f "%Y-%m-%d %H:%M:%S" "$enc_date" "+%s" 2>/dev/null) || continue

    offset=$(( ep - first_epoch ))
    [ $offset -lt 0 ] && offset=0      # shouldn’t happen, but be safe

    hh=$(( offset / 3600 ))
    mm=$(( (offset % 3600) / 60 ))
    ss=$(( offset % 60 ))
    tc=$(printf "%02d:%02d:%02d:00" "$hh" "$mm" "$ss")

    echo "[$f]  offset=${offset}s  =>  time-code $tc"

    tmp="${f%.*}.__tc__.mp4"
    ffmpeg -loglevel error -y -i "$f" \
           -codec copy \
           -timecode "$tc" \
           "$tmp"

    mv -f "$tmp" "$f"
done

echo "All done."