# Using Raspberry Pi Camera with ffmpeg

Capturing video from the rpi camera with ffmpeg can vary from less than 5% to 100% of the CPU (rpi zero) depending on ffmpeg using the hardware acceleration or not.

On many github issues one finds the suggestion of using `h264_omx` codec to use the gpu - but it does not ship with the default `ffmpeg` on Raspbian.

Instead I found that one can use the v4l2 driver provided by raspbian to get hardware accelerated h264 output. Also setting the video size will save one from using a (cpu) scale filter.

## ffmpeg
capture h264 video from rpi camera

```bash
ffmpeg -f video4linux2 -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vcodec copy -an test.h264
```

capture jpg image from rpi camera

```bash
ffmpeg -f video4linux2 -input_format mjpeg -video_size 1280x720 -i /dev/video0 -vframes 1 -f mjpeg -
```

Note:
`ffmpeg` currently does not support setting the bitrate of v4l2 devices [see bug report](https://trac.ffmpeg.org/ticket/6639) - call `v4l2-ctl --set-ctrl video_bitrate=300000` instead (setting to 300k) 

v4l2 driver swithing to "stills mode" `modprobe bcm2835-v4l2 max_video_width=2592 max_video_height=1944` [source](https://github.com/Motion-Project/motion/issues/375#issuecomment-304304885)

## nodejs example for use with homebridge

Use [homebridge-camera-rpi](https://github.com/moritzmhmk/homebridge-camera-rpi):

```bash
npm install -g homebridge-camera-rpi
```

### Code

handleSnapshotRequest and handleStreamRequest for [hap-nodejs](https://github.com/KhaosT/HAP-NodeJS/blob/master/lib/Camera.js) or [homebridge-camera-ffmpeg](https://github.com/KhaosT/homebridge-camera-ffmpeg/blob/master/ffmpeg.js)

```js
var spawn = require('child_process').spawn
```

...

```js
handleSnapshotRequest = function (request, callback) {
  let ffmpegCommand = `\
-f video4linux2 -input_format mjpeg -video_size ${request.width}x${request.height} -i /dev/video0 \
-vframes 1 -f mjpeg -`
  console.log(ffmpegCommand)
  let ffmpeg = spawn('ffmpeg', ffmpegCommand.split(' '), {env: process.env})
  var imageBuffer = Buffer(0)
  ffmpeg.stdout.on('data', function (data) { imageBuffer = Buffer.concat([imageBuffer, data]) })
  ffmpeg.stderr.on('data', function (data) { console.log('ffmpeg', String(data)) })
  ffmpeg.on('close', function (code) { callback(undefined, imageBuffer) })
}
```

...

```js
handleStreamRequest = function (request) {
  var sessionID = request['sessionID']
  var requestType = request['type']
  if (!sessionID) return
  let sessionIdentifier = uuid.unparse(sessionID)

  if (requestType === 'start' && this.pendingSessions[sessionIdentifier]) {
    var width = 1280
    var height = 720
    var fps = 30
    var bitrate = 300

    if (request['video']) {
      width = request['video']['width']
      height = request['video']['height']
      fps = Math.min(fps, request['video']['fps'])
      bitrate = request['video']['max_bit_rate']
    }

    let srtp = this.pendingSessions[sessionIdentifier]['video_srtp'].toString('base64')
    let address = this.pendingSessions[sessionIdentifier]['address']
    let port = this.pendingSessions[sessionIdentifier]['video_port']

    let ffmpegCommand = `\
-f video4linux2 -input_format h264 -video_size ${width}x${height} -framerate ${fps} -i /dev/video0 \
-vcodec copy -an -payload_type 99 -ssrc 1 -f rtp \
-srtp_out_suite AES_CM_128_HMAC_SHA1_80 -srtp_out_params ${srtp} \
srtp://${address}:${port}?rtcpport=${port}&localrtcpport=${port}&pkt_size=1378`
    console.log(ffmpegCommand)
    let ffmpeg = spawn('ffmpeg', ffmpegCommand.split(' '), {env: process.env})
    ffmpeg.stderr.on('data', function (data) { console.log('ffmpeg', String(data)) })
    this.ongoingSessions[sessionIdentifier] = ffmpeg

    delete this.pendingSessions[sessionIdentifier]
  }
  if (requestType === 'stop' && this.ongoingSessions[sessionIdentifier]) {
    this.ongoingSessions[sessionIdentifier].kill('SIGKILL')
    delete this.ongoingSessions[sessionIdentifier]
  }
}
```