feat: Write colr atom to muxed mp4

[CaitlinOCallaghan]

This PR is an extension of the full AV1 codec string feature: PR 1205 and relates to Issue 1007 and Issue 1202.

As per the AV1 spec, the codec string may contain optional color values. These color values are critical for detecting HDR video streams - see Issue 1007. Color information is extracted from the input mp4's colr atom and used to generate the full AV1 codec string. This PR preserves the color information by writing the colr atom to the muxed mp4.

References:

• AV1 Codec ISO Media File Format Binding
• AV1 Bitstream & Decoding Process
  Specification - Section 6.4.2 Color config semantics (page 117)
• QuickTime File Format Specification

Testing

Manual: AV1 video WITH colr atom

Note: Presence of the colr atom in bbbhdr_av1.mp4 was verified with a hex editor.

1. Generate Packager MPD with: ./out/Release/packager in=~/Downloads/bbbhdr_av1.mp4,stream=video,output=av1_with_colr.mp4 --mpd_output av1_with_colr.mpd
2. Check manifest generated by Shaka Packager for Representation codecs string:

<?xml version="1.0" encoding="UTF-8"?>
<!--Generated with https://github.com/shaka-project/shaka-packager version 31129ee-release-->
<MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" minBufferTime="PT2S" type="static" mediaPresentationDuration="PT1.100000023841858S">
  <Period id="0">
    <AdaptationSet id="0" contentType="video" width="640" height="360" frameRate="15360/512" subsegmentAlignment="true" par="16:9">
      <Representation id="0" bandwidth="778146" codecs="av01.1.01M.10.0.000.09.16.09.0" mimeType="video/mp4" sar="1:1">
        <BaseURL>av1_with_colr.mp4</BaseURL>
        <SegmentBase indexRange="808-851" timescale="15360">
          <Initialization range="0-807"/>
        </SegmentBase>
      </Representation>
    </AdaptationSet>
  </Period>
</MPD>

3. Check av1_with_colr.mp4 bitstream for the colr atom and cross reference the values of the atom's properties with the codec representation string found in the manifest:
   

Format

git clang-format --style Chromium --binary /usr/bin/clang-format 80e024013df87a4bfeb265c8ea83cfa2a0c5db0f

BEGIN_COMMIT_OVERRIDE
feat: Write colr atom to muxed mp4 (#1261)
Closes #1202
END_COMMIT_OVERRIDE

[cosmin]

This approach seems much cleaner to me compared to the previous attempt at re-creating the colr box from the codec string.