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This page outlines some best practices; however, we advise to always consult a TSG member if you plan to run a video experiment in the labs.
This page outlines some best practices; however, we advise to always consult a TSG member if you plan to run a video experiment in the labs.
==Recording==
==Video encoding==
When recording video for stimulus material or as input for your experiment, please:
When recording video for stimulus material or as input for your experiment, please:
Use a high-quality camera, with settings appropriate for your application (e.g., frame rate, resolution).
Use a high-quality camera, with settings appropriate for your application (e.g., frame rate, resolution).
Record in a controlled environment with consistent lighting and minimal background distractions.
Record in a controlled environment with consistent lighting and minimal background distractions.
You can use the facecam for high quality video recording.
You can use the facecam for high quality video recording.
==Audio encoding==
• Codec: Use lossless or high-quality codecs to preserve timing:
o PCM (WAV): Best for accuracy, as it is uncompressed and avoids delays.
o AAC (Advanced Audio Codec): Good compromise between quality and size.
• Sample Rate: Use a standard sample rate (e.g., 44.1 kHz or 48 kHz) for synchronization with video.
o Example: -ar 44100 for 44.1 kHz.
• Channel Count: Maintain the original channel configuration (e.g., stereo or mono) for time-accurate playback.
==Synchronization==
• Ensure the audio and video streams have consistent timestamps:
o FFmpeg Options:
-fflags +genpts: Generates accurate presentation timestamps (PTS) for the video.
-async 1: Synchronizes audio and video when they drift.
-map 0:v:0 and -map 0:a:0: Explicitly map video and audio streams to avoid accidental mismatches.
==Editing==
==Editing==
We recommend using DaVinci Resolve for editing and converting video files. DaVinci Resolve is a free, professional-grade editing program, available here: https://www.blackmagicdesign.com/products/davinciresolve
We recommend using DaVinci Resolve for editing and converting video files. DaVinci Resolve is a free, professional-grade editing program, available here: https://www.blackmagicdesign.com/products/davinciresolve
==Recommended FFmpeg Command==
Here’s a command that encodes video and audio while maintaining high time accuracy:
ffmpeg -i input.mp4 \
-c:v libx264 -preset slow -crf 18 -vsync cfr -g 30 \
-c:a pcm_s16le -ar 44100 \
-fflags +genpts -async 1 \
output.mp4
• -c:v libx264: Encode video using H.264.
• -preset slow: Optimize for quality and compression efficiency.
• -crf 18: Adjusts quality (lower = better; range: 0–51).
• -vsync cfr: Enforces constant frame rate.
• -c:a pcm_s16le: Encodes audio in uncompressed WAV format.
• -ar 44100: Sets audio sample rate to 44.1 kHz.
• -fflags +genpts: Ensures accurate timestamps.
• -async 1: Synchronizes audio and video streams.
===Tips===
• Ensure Low Latency: If you're processing video/audio in real time, use low-latency settings (e.g., -tune zerolatency for H.264).
• Avoid Resampling: If possible, use the original frame rate and sample rate to avoid timing mismatches.
• Testing: Always test playback on different devices or players to confirm synchronization.
Alternatively, you can use Shotcut, a simple open-source editor, available here: https://shotcut.org/
Alternatively, you can use Shotcut, a simple open-source editor, available here: https://shotcut.org/