Skip to content

Commit

Permalink
Merge pull request #713 from AOMediaCodec/issue_681
Browse files Browse the repository at this point in the history 
SHA: d0d828c
Reason: push, by sunghee-hwang

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
  • Loading branch information
@sunghee-hwang @github-actions
sunghee-hwang and github-actions[bot] committed Aug 21, 2023
1 parent c7643f9 commit 263336c
Showing 1 changed file with 3 additions and 3 deletions.
6 changes: 3 additions & 3 deletions index.html
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1490,7 +1490,7 @@
</style>
<meta content="Bikeshed version 6edc88947, updated Thu Aug 17 11:18:09 2023 -0700" name="generator">
<link href="https://aomediacodec.github.io/iamf/" rel="canonical">
<meta content="7637bbfc056f8acd88e1dfd34f62f2385919c5ae" name="document-revision">
<meta content="d0d828c4c20d9db9d31a5d0be05cf3b8c949ccd2" name="document-revision">
<style>/* Boilerplate: style-autolinks */
.css.css, .property.property, .descriptor.descriptor {
color: var(--a-normal-text);
Expand Down Expand Up @@ -2519,7 +2519,7 @@ <h3 class="heading settled" data-level="3.4" id="obu-iasequenceheader"><span cla
</pre>
<p><b>Semantics</b></p>
<p><dfn data-dfn-type="dfn" data-noexport id="ia_code">ia_code<a class="self-link" href="#ia_code"></a></dfn> is a ‘four-character code’ (4CC), <code>iamf</code>.</p>
<p class="note" role="note"><span class="marker">NOTE:</span> When IA OBUs are delivered over a protocol that does not provide explicit <a data-link-type="dfn" href="#ia-sequence" id="ref-for-ia-sequence②⓪">IA Sequence</a> boundaries, a parser may locate the <a data-link-type="dfn" href="#ia-sequence" id="ref-for-ia-sequence②①">IA Sequence</a> start by searching for the code <code>iamf</code> preceded by specific OBU header values. For example, by assuming that <a data-link-type="dfn" href="#obu_extension_flag" id="ref-for-obu_extension_flag①">obu_extension_flag</a> is set to 0 and because <a data-link-type="dfn" href="#obu_trimming_status_flag" id="ref-for-obu_trimming_status_flag">obu_trimming_status_flag</a> is set to 0 for an <a data-link-type="dfn" href="#ia-sequence-header-obu" id="ref-for-ia-sequence-header-obu⑤">IA Sequence Header OBU</a>, the OBU header can be 0xF806 or 0xFC06.</p>
<p class="note" role="note"><span class="marker">NOTE:</span> When IA OBUs are delivered over a protocol that does not provide explicit <a data-link-type="dfn" href="#ia-sequence" id="ref-for-ia-sequence②⓪">IA Sequence</a> boundaries, a parser may locate the <a data-link-type="dfn" href="#ia-sequence" id="ref-for-ia-sequence②①">IA Sequence</a> start by searching for the code <code>iamf</code> preceded by specific OBU header values. For example, by assuming that <a data-link-type="dfn" href="#obu_extension_flag" id="ref-for-obu_extension_flag①">obu_extension_flag</a> is set to 0 and because <a data-link-type="dfn" href="#obu_trimming_status_flag" id="ref-for-obu_trimming_status_flag">obu_trimming_status_flag</a> is set to 0 for an <a data-link-type="dfn" href="#ia-sequence-header-obu" id="ref-for-ia-sequence-header-obu⑤">IA Sequence Header OBU</a>, the OBU header can be either 0xF806 or 0xFC06.</p>
<p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="primary_profile">primary_profile</dfn> indicates the primary profile that this <a data-link-type="dfn" href="#ia-sequence" id="ref-for-ia-sequence②②">IA Sequence</a> complies with. Parsers compliant with this version of the specification SHOULD discard the <a data-link-type="dfn" href="#ia-sequence" id="ref-for-ia-sequence②③">IA Sequence</a> if they do not support the value indicated here.</p>
<p>The mappings below are applied for both <a data-link-type="dfn" href="#primary_profile" id="ref-for-primary_profile">primary_profile</a> and <a data-link-type="dfn" href="#additional_profile" id="ref-for-additional_profile">additional_profile</a>.</p>
<ul>
Expand Down Expand Up @@ -2563,7 +2563,7 @@ <h3 class="heading settled" data-level="3.5" id="obu-codecconfig"><span class="s
<p>Parsers compliant with this version of the specification SHOULD ignore <a data-link-type="dfn" href="#codec-config-obu" id="ref-for-codec-config-obu③">Codec Config OBU</a>s with an unknown <a data-link-type="dfn" href="#codec_id" id="ref-for-codec_id①">codec_id</a>.</p>
<p class="note" role="note"><span class="marker">NOTE:</span> <a class="property css" data-link-type="property" href="https://www.iso.org/standard/77752.html#" id="ref-for-something④">ipcm</a> should not be confused with <code>lpcm</code>, which is another 4CC to identify codecs in other container formats (e.g., QuickTime).</p>
<p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="num_samples_per_frame">num_samples_per_frame</dfn> indicates the frame length, in samples, of the <a data-link-type="dfn" href="#audio_frame" id="ref-for-audio_frame">audio_frame()</a> provided in the <code>audio_frame_obu</code>. It SHALL NOT be set to zero. If the <a data-link-type="dfn" href="#decoder_config" id="ref-for-decoder_config④">decoder_config()</a> structure for a given codec specifies a value for the frame length, the two values SHALL be equal.</p>
<p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="audio_roll_distance">audio_roll_distance</dfn> indicates how many audio frames prior to the current audio frame need to be decoded (and the decoded samples discarded) to set the encoder in a state that will produce the perfect decoded audio signal. It SHALL always be a negative value or zero. For some audio codecs, even if an audio frame can be decoded independently, the decoded signal after decoding only that frame may not represent a perfect, decoded audio signal, even ignoring compression artifacts. This can be due to overlap transforms. While potentially acceptable when starting to decode an <a data-link-type="dfn" href="#audio-substream" id="ref-for-audio-substream④⓪">Audio Substream</a>, it may be problematic when automatically switching between similar <a data-link-type="dfn" href="#audio-substream" id="ref-for-audio-substream④①">Audio Substream</a>s of different quality and/or bitrate.</p>
<p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="audio_roll_distance">audio_roll_distance</dfn> indicates how many audio frames prior to the current audio frame need to be decoded (and the decoded samples discarded) to set the decoder in a state that will produce the perfect decoded audio signal. It SHALL always be a negative value or zero. For some audio codecs, even if an audio frame can be decoded independently, the decoded signal after decoding only that frame may not represent a perfect, decoded audio signal, even ignoring compression artifacts. This can be due to overlap transforms. While potentially acceptable when starting to decode an <a data-link-type="dfn" href="#audio-substream" id="ref-for-audio-substream④⓪">Audio Substream</a>, it may be problematic when automatically switching between similar <a data-link-type="dfn" href="#audio-substream" id="ref-for-audio-substream④①">Audio Substream</a>s of different quality and/or bitrate.</p>
<ul>
<li data-md>
<p>It SHALL be set to -R when <a data-link-type="dfn" href="#codec_id" id="ref-for-codec_id②">codec_id</a> is set to <a class="property css" data-link-type="property" href="https://opus-codec.org/docs/opus_in_isobmff.html#" id="ref-for-something⑤">Opus</a>, where R is <code>ceil(3840 / <a data-link-type="dfn" href="#num_samples_per_frame" id="ref-for-num_samples_per_frame③">num_samples_per_frame</a>)</code>.</p>
Expand Down

0 comments on commit 263336c

Please sign in to comment.