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Created September 28, 2024 13:22
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ffmpeg live capture.md

USB Video Capture with FFmpeg

This guide explains how to capture video and audio from a USB capture device and process it using FFmpeg in two steps. The current method captures video at a custom frame rate with sound, followed by a second step to process the video.

Step 1: Capture Video and Audio

The first command captures both video and audio using a USB video capture device and a virtual audio source. It records the video at 34 frames per second for 200 seconds.

ffmpeg -f dshow -rtbufsize 100M -i video="usb video" -f dshow -i audio="virtual-audio-capturer" -preset ultrafast -framerate 34 -t 200 -y output2.mp4
  • -f dshow: Uses DirectShow as the input format for capturing video and audio.
  • -rtbufsize 100M: Sets the buffer size for real-time capture.
  • -i video="usb video": Specifies the USB video capture device.
  • -i audio="virtual-audio-capturer": Specifies the virtual audio capture source.
  • -preset ultrafast: Uses the fastest compression preset.
  • -framerate 34: Sets the frame rate to 34 fps.
  • -t 200: Limits the capture duration to 200 seconds.
  • -y output2.mp4: Overwrites the output file output2.mp4 if it already exists.

Step 2: Process the Captured Video

The second command takes the captured video file output2.mp4 and processes it to ensure compatibility by converting it to the H.264 codec with AAC audio.

ffmpeg -y -i ".\output2.mp4" -pix_fmt yuv420p -vcodec h264 -t 60 -acodec aac -ac 2 ".\final_video.mp4"
  • -pix_fmt yuv420p: Ensures compatibility by using the YUV420p pixel format.
  • -vcodec h264: Converts the video to H.264 format.
  • -t 60: Limits the output video to 60 seconds.
  • -acodec aac: Encodes the audio in AAC format.
  • -ac 2: Uses 2-channel stereo audio.
  • -y final_video.mp4: Overwrites the output file final_video.mp4 if it already exists.

Proposed Single Command (Not Tested)

To merge both commands into one, you can try the following approach, although it has not been tested:

ffmpeg -f dshow -rtbufsize 100M -i video="usb video" -f dshow -i audio="virtual-audio-capturer" -preset ultrafast -framerate 34 -t 60 -pix_fmt yuv420p -vcodec h264 -acodec aac -ac 2 -y final_video.mp4

This single command attempts to capture and process the video in one step. Be sure to test it to confirm its effectiveness.

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