SimpleBlock encoding support

[umstek]

I'm trying to parse a webm file, drop some SimpleBlocks, and adjust the Timecodes on each block so that I can effectively trim the video. I can create Clusters and Cluster Timecodes without an issue but encoding a SimpleBlocks is a problem. Although there is an Encoder() present, there seems to be no way to create/edit a SimpleBlock. I'm looking a function that can do the inverse of tools.readBlock.

(Currently I'm using ffmpeg (wasm) but it's a bit expensive on data.)

[alx696]

@umstek Have you found a solution?

I'm trying to play webm chunks with MediaSource. I want to skip the chunks before open stream. So i can play the stream anytime. WebM was recorded by MediaRecorder.

Some of them have been deleted, but times not right:

new Blob(
                [
                    webmChunkBufferArray.shift(),
                    webmChunkBufferArray.shift(),
                    webmChunkBufferArray.shift()
                ],
                {
                    type: mimeType
                }
            ).arrayBuffer()
            .then(buffer => {
                const decoder = new Decoder();
                const elms = decoder.decode(buffer);
                console.debug(elms);

                const recodeArray = [];
                let count = 0;
                for(const elm of elms) {
                    if (elm.name === "SimpleBlock" && count < 100) {
                        count ++;
                        continue;
                    }

                    recodeArray.push(elm);
                }
                console.debug(recodeArray);

                const encoder = new Encoder();
                const recodeBuffer = encoder.encode(recodeArray);
                console.debug(recodeBuffer);

                sourceBuffer.mode = 'sequence'; // must set!
                sourceBuffer.appendBuffer(recodeBuffer);
            });

But i do not know how to get SimpleBlock from mediaRecorder.ondataavailable() stream?

new Decoder().decode(buffer): buffer must start from the begin of the webm. If not, decode failure.