demo · v138

Encode → decode carriage check

An Android camera can capture sensor-native pixels and attach portrait orientation as VideoFrame metadata. Run a VP8 WebCodecs round-trip and inspect whether the decoded frame keeps rotation + flip or comes back normalized for this codec/backend.

checking VideoEncoder/Decoder support…

1. source frame from camera

2. after encode → chunk → decode

3. rendered from decoded metadata or sidecar

the trick

// 1. wrap the captured pixels with orientation metadata
const sourceFrame = new VideoFrame(srcCanvas, {
  timestamp: 0,
  rotation: 90,              // NEW in 138
  flip: true,                // NEW in 138 (horizontal mirror)
});

// 2. encode it
encoder.encode(sourceFrame);

// 3. on the decoder side, inspect what the codec returned.
const decoder = new VideoDecoder({
  output: (frame) => {
    const preserved =
      frame.rotation === sourceFrame.rotation &&
      frame.flip === sourceFrame.flip;
    console.log(frame.rotation, frame.flip, preserved);
    frame.close();
  },
  error: console.error,
});

Before Chrome 138, decoded frames had no standard rotation / flip fields to inspect. The fields now exist on VideoFrame; whether an encode/decode path serializes them is still codec and backend specific, so production pipelines should verify the path and keep a sidecar/container value when needed.

see also