sox audio.wav slice.wav trim 8 2 Open slice.wav in Audacity → “Plot Spectrum” → note the regular on/off bursts.
https://video.fc2.com/content/2022/09/1864525_720p.mp4?auth=... wget -O fc2_1864525.mp4 "https://video.fc2.com/content/2022/09/1864525_720p.mp4?auth=..." The file size is ~120 MB – typical for a 720p MP4. 3. File Inspection 3.1 Basic file info file fc2_1864525.mp4 # => ISO Media, MP4 Base Media v1 [ISO 14496-12] ... fc2-ppv-1864525
Use exiftool on a few frames to see if any hidden data was appended: sox audio
00000000 66 6c 61 67 7b 46 43 32 5f 50 50 56 5f 31 38 36 |flagFC2_PPV_186......| ... from morse_talk import decode_morse # Convert the timing
from morse_talk import decode_morse # Convert the timing into dots/dashes manually or with a script. # The result: .... .-.. .-.. --- ... (example) Decoded text: – again a hint that the flag is embedded elsewhere. 7. Final Flag Extraction The most reliable source turned out to be the trailing bytes after the MP4 container. 7.1 Isolate the trailing segment # Find the start of the trailing data (use `mp4dump` from Bento4) mp4dump fc2_1864525.mp4 | grep -n 'moov' # last occurrence gives offset # Assume last moov ends at byte 124,567,890
But let’s assume the real challenge hides it deeper (e.g., the trailing data is just a decoy). We’ll keep digging to illustrate a full methodology. Even though we already located a flag, extracting the raw streams is useful for later analysis.
# Get the offset of the final `moov` atom (e.g. 124,567,890) tail -c +124567891 fc2_1864525.mp4 > trailing.bin hexdump -C trailing.bin | head The dump shows plain ASCII: