Record & live preview V4L2 /dev/video0 to H264 file with GStreamer

Question

How to record only video from V4L2 input device and encode it to a file using H.264 while seeing a live preview of the input at the same time?

• Using GStreamer GStreamer 0.10.36
  Command gst-launch-1.0

• Using v4l-utils 1.6.3-3
  Command v4l2-ctl

Answer 1

Determine available resolutions and formats:

v4l2-ctl -d /dev/video0 --list-formats-ext

---

Preview, record & encode at the same time:

• "format", "width", "height" and "framerate" need to be filled in.

• "keyframe_period" specifies how often a keyframe appears in the video, which is used for reconstruction of a video frame and (to my understanding) seeking.

• "min-qp" specifies compression quality where lower means better quality.

:

gst-launch-1.0 v4l2src device=/dev/video0 ! \
    video/x-raw,format=YV12,width=960,height=544,framerate=30/1 ! \
    tee name=t ! \
    queue ! \
    autovideosink sync=false t. ! \
    videorate ! \
    queue ! \
    vaapiencode_h264 keyframe_period=5 tune=high-compression min-qp=50 ! \
    queue ! \
    mpegtsmux ! \
    filesink location=FIRST.mp4

(For some reason the resulting FIRST.mp4 cannot be seeked. Something about invalid timestamps.)

Rebuilding the mp4 container without re-encoding produces a seekable mp4 file:

ffmpeg -i FIRST.mp4 -c:v copy SECOND.mp4