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Author: javascript-2020

blog/25-11-15/ex/webcodec-api.js

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+// Assuming you have:
+// - an H.264 IDR (keyframe) NAL unit(s) as a Uint8Array: keyframeBytes
+// - optional following delta frame(s): deltaBytes
+// - SPS and PPS NAL units extracted as Uint8Array: spsBytes, ppsBytes
+
+// Build an AVCDecoderConfigRecord (description) by concatenating SPS/PPS in Annex B or AVCC form.
+// For AVCC, you need a proper 'description' (AVCDecoderConfigurationRecord) buffer.
+// For a quick start, many browsers accept Annex B with parameter sets in 'description' too.
+
+        
+        var config = {
+              codec: 'avc1.42E01E', // baseline profile example; replace if needed
+              description: buildAvcDecoderConfigRecord(spsBytes, ppsBytes) // Uint8Array
+        };
+        
+        var decoder = new VideoDecoder({
+              output: async (frame) => {
+                    // Draw to canvas
+                    var bitmap = await createImageBitmap(frame);
+                    var canvas = document.createElement('canvas');
+                    canvas.width = bitmap.width;
+                    canvas.height = bitmap.height;
+                    var ctx = canvas.getContext('2d');
+                    ctx.drawImage(bitmap, 0, 0);
+                    bitmap.close();
+                    frame.close();
+        
+                    // Export JPEG
+                    canvas.toBlob(
+                          (blob) => {
+                                // blob is a JPEG; do something with it (download, upload, etc.)
+                                // e.g., createObjectURL(blob) for preview
+                          },
+                          'image/jpeg',
+                          0.92
+                    );
+              },
+              error: (e) => console.error('Decode error', e)
+        });
+        
+        decoder.configure(config);
+        
+        // Wrap raw H.264 bytes into EncodedVideoChunks (Annex B or AVCC formatted appropriately)
+        // The 'type' must be 'key' for IDR frames and 'delta' for non-key frames.
+        
+        function makeChunk(bytes, timestamp, isKey) {
+              return new EncodedVideoChunk({
+                    timestamp, // in microseconds if you care
+                    type: isKey ? 'key' : 'delta',
+                    data: bytes
+              });
+        }
+        
+        // Feed the keyframe first
+        decoder.decode(makeChunk(keyframeBytes, 0, true));
+        
+        // Optionally feed the next frame(s)
+        decoder.decode(makeChunk(deltaBytes, 33333, false)); // ~30fps timestamp