mirror of
https://github.com/shaka-project/shaka-player.git
synced 2026-06-17 16:26:39 +03:00
Muhammad Haris
480d4a801a
This is an MP4 Parser which extracts CEA-708 packets from Fragmented MP4 streams. The Closed Caption Parser (shaka.media.ClosedCaptionParser) will own this MP4 Parser, and will initialize it and call it as shown. As data comes in, the parser will parse this data, and the caption packets data then be returned in a callback (on708Data), as shown. Here, a theoretical decoder (future pull request, mentioned as a Todo comment) will decode and extract the parsed captions from these packets. Issue #2648
78 lines
2.0 KiB
JavaScript
78 lines
2.0 KiB
JavaScript
/*! @license
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* Shaka Player
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* Copyright 2016 Google LLC
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* SPDX-License-Identifier: Apache-2.0
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*/
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goog.provide('shaka.cea.SeiProcessor');
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/**
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* H.264 SEI NALU Parser used for extracting 708 closed caption packets.
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*/
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shaka.cea.SeiProcessor = class {
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/**
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* Processes supplemental enhancement information data.
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* @param {!Uint8Array} naluData NALU from which SEI data is to be processed.
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* @return {!Iterable.<!Uint8Array>}
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*/
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* process(naluData) {
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const emuCount = this.removeEmu_(naluData);
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// The following is an implementation of section 7.3.2.3.1
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// in Rec. ITU-T H.264 (06/2019), the H.264 spec.
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let offset = 0;
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while (offset + emuCount < naluData.length) {
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let payloadType = 0; // SEI payload type as defined by H.264 spec
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while (naluData[offset] == 0xFF) {
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payloadType += 255;
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offset++;
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}
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payloadType += naluData[offset++];
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let payloadSize = 0; // SEI payload size as defined by H.264 spec
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while (naluData[offset] == 0xFF) {
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payloadSize += 255;
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offset++;
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}
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payloadSize += naluData[offset++];
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// Payload type 4 is user_data_registered_itu_t_t35, as per the H.264
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// spec. This payload type contains caption data.
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if (payloadType == 0x04) {
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yield naluData.subarray(offset, offset + payloadSize);
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}
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offset += payloadSize;
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}
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}
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/**
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* Removes H.264 emulation prevention bytes from the byte array.
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* @param {!Uint8Array} naluData NALU from which EMUs should be removed.
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* @return {number} The number of removed emulation prevention bytes.
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* @private
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*/
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removeEmu_(naluData) {
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let zeroCount = 0;
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let src = 0;
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let dst = 0;
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while (src < naluData.length) {
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if (zeroCount == 2 && naluData[src] == 0x03) {
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zeroCount = 0;
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} else {
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if (naluData[src] == 0x00) {
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zeroCount++;
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} else {
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zeroCount = 0;
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}
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naluData[dst] = naluData[src];
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dst++;
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}
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src++;
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}
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return (src - dst);
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}
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};
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