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createVideoDecoder()v4.0.307

This function is a wrapper around the VideoDecoder Web API.

Create a video decoder
tsx
import {createVideoDecoder} from '@remotion/webcodecs';
 
const decoder = createVideoDecoder({
  track,
  onFrame: console.log,
  onError: console.error,
});

Differences to VideoDecoder​

API​

Takes an object with the following properties:

track​

An VideoDecoderConfig object.
You may pass a MediaParserVideoTrack object from parseMedia(), which also is an VideoDecoderConfig object.

onFrame​

A callback that is called when a frame is decoded.

Takes a single argument, which is a VideoFrame object.

If the passed callback is asynchronous, the queue size counter will be decreased only after the callback has been resolved.

However, the callback for the next frame may already be called while your callback is still running.
We do not ensure that callbacks are running sequentially.

onError​

A callback that is called when an error occurs or the decode is aborted through the controller.

Takes a single argument, which is an Error object.

controller?​

A webcodecsController() instance.

If provided, you can call .pause(), .resume() and .abort() on the controller to pause, resume and abort the decoding.

logLevel?​

string LogLevel

One of "error", "warn", "info", "debug", "trace".
Default value: "info", which logs only important information.

Return type​

Returns an object with the following properties:

waitForQueueToBeLessThan()​

Pass a number to wait for the queue to be less than the given number.

A promise that resolves when the queue size is less than the given number.
The queue is only decremented when the onFrame callback resolves.

flush()​

Flushes the decoder, forcing the queue to be cleared. Returns a promise that resolves when all frames have been cleared and the onFrame() callback has beeen resolved for all frames.

reset()​

Clears the queue and resets the decoder. Same as VideoDecoder.reset() + VideoDecoder.configure().

close()​

Closes the decoder. Same as AudioDecoder.close().

checkReset()v4.0.312​

Returns a handle with a wasReset() function. If the decoder was reset inbetween the call to .checkReset() and the call to wasReset(), wasReset() will return true. See below for an example.

getMostRecentSampleInput()v4.0.312​

Return the .timestamp of the most recently input sample.

Example usage with @remotion/media-parser​

Decode a video track
tsx
import {parseMedia} from '@remotion/media-parser';
import {createVideoDecoder} from '@remotion/webcodecs';
 
await parseMedia({
  src: 'https://parser.media/video.mp4',
  onVideoTrack: ({track, container}) => {
    const decoder = createVideoDecoder({
      track,
      onFrame: console.log,
      onError: console.error,
    });
 
    return async (sample) => {
      // Called on every sample
      await decoder.waitForQueueToBeLessThan(10);
      await decoder.decode(sample);
 
      return async () => {
        // Called when the track is done
        await decoder.flush();
        decoder.close();
      };
    };
  },
});

Checking if the decoder was reset​

A potential race condition you may face is that decoder.reset() is called while a sample is waiting for the queue to be less than a certain number. Use .checkReset() to check if the decoder was reset after any asynchronous operation, and abort the processing of the sample if needed.

Check if the decoder was reset
tsx
import {parseMedia} from '@remotion/media-parser';
import {createVideoDecoder} from '@remotion/webcodecs';
 
await parseMedia({
  src: 'https://parser.media/video.mp4',
  onVideoTrack: ({track, container}) => {
    const decoder = createVideoDecoder({
      track,
      onFrame: console.log,
      onError: console.error,
    });
 
    return async (sample) => {
      const {wasReset} = decoder.checkReset();
 
      await decoder.waitForQueueToBeLessThan(10);
      if (wasReset()) {
        return
      }
 
      await decoder.decode(sample);
      if (wasReset()) {
        return;
      }
 
      return async () => {
        if (wasReset()) {
          return;
        }
 
        // Called when the track is done
        await decoder.flush();
        decoder.close()
      };
    };
  },
});

See also​