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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<title>get_next_access_unit.py.html</title>
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<font color="#0000ff"># Pseudo-Python rendition of the code for ``get_next_access_unit()``.</font><br>
<br>
<font color="#0000ff"># ***** BEGIN LICENSE BLOCK *****</font><br>
<font color="#0000ff"># Version: MPL 1.1</font><br>
<font color="#0000ff"># </font><br>
<font color="#0000ff"># The contents of this file are subject to the Mozilla Public License Version</font><br>
<font color="#0000ff"># 1.1 (the "License"); you may not use this file except in compliance with</font><br>
<font color="#0000ff"># the License. You may obtain a copy of the License at</font><br>
<font color="#0000ff"># <a href="http://www.mozilla.org/MPL/">http://www.mozilla.org/MPL/</a></font><br>
<font color="#0000ff"># </font><br>
<font color="#0000ff"># Software distributed under the License is distributed on an "AS IS" basis,</font><br>
<font color="#0000ff"># WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License</font><br>
<font color="#0000ff"># for the specific language governing rights and limitations under the</font><br>
<font color="#0000ff"># License.</font><br>
<font color="#0000ff"># </font><br>
<font color="#0000ff"># The Original Code is the MPEG TS, PS and ES tools.</font><br>
<font color="#0000ff"># </font><br>
<font color="#0000ff"># The Initial Developer of the Original Code is Amino Communications Ltd.</font><br>
<font color="#0000ff"># Portions created by the Initial Developer are Copyright (C) 2008</font><br>
<font color="#0000ff"># the Initial Developer. All Rights Reserved.</font><br>
<font color="#0000ff"># </font><br>
<font color="#0000ff"># Contributor(s):</font><br>
<font color="#0000ff"># Amino Communications Ltd, Swavesey, Cambridge UK</font><br>
<font color="#0000ff"># </font><br>
<font color="#0000ff"># ***** END LICENSE BLOCK *****</font><br>
<br>
<font color="#a52a2a"><b>def</b></font> <font color="#008b8b">get_next_access_unit</font>(context):<br>
<span style="background-color: #f2f2f2"><font color="#ff00ff">"""Retrieve the next access unit from the file described by `context`.</font></span><br>
<span style="background-color: #f2f2f2"><font color="#ff00ff"> """</font></span><br>
access_unit = build_access_unit()<br>
<font color="#a52a2a"><b>if</b></font> context.pending_nal: <font color="#0000ff"># i.e., we already had a NAL to start this unit</font><br>
access_unit.append(context.pending_nal,TRUE,context.pending_list)<br>
context.pending_nal = NULL<br>
context.pending_list.reset(FALSE)<br>
<br>
<font color="#a52a2a"><b>while</b></font> <span style="background-color: #f2f2f2"><font color="#ff00ff">1</font></span>:<br>
<font color="#a52a2a"><b>try</b></font>:<br>
nal = context.find_next_NAL_unit()<br>
<font color="#a52a2a"><b>except</b></font> EOF:<br>
context.no_more_data = TRUE; <font color="#0000ff"># prevent future reads on this stream</font><br>
<font color="#a52a2a"><b>break</b></font><br>
<font color="#a52a2a"><b>except</b></font> BrokenNALUnit:<br>
WARNING(<span style="background-color: #f2f2f2"><font color="#ff00ff">"!!! Ignoring broken NAL unit</font></span><span style="background-color: #f2f2f2"><font color="#6a5acd">\n</font></span><span style="background-color: #f2f2f2"><font color="#ff00ff">"</font></span>)<br>
access_unit.ignored_broken_NAL_units += <span style="background-color: #f2f2f2"><font color="#ff00ff">1</font></span><br>
<font color="#a52a2a"><b>continue</b></font><br>
<br>
<font color="#a52a2a"><b>if</b></font> nal.is_slice():<br>
<font color="#a52a2a"><b>if</b></font> <font color="#a52a2a"><b>not</b></font> access_unit.started_primary_picture:<br>
<font color="#0000ff"># We're in a new access unit, but we haven't had a slice</font><br>
<font color="#0000ff"># yet, so we can be lazy and assume that this must be the</font><br>
<font color="#0000ff"># first slice</font><br>
nal.start_reason = <span style="background-color: #f2f2f2"><font color="#ff00ff">"First slice of new access unit"</font></span><br>
access_unit.append(nal,TRUE,context.pending_list)<br>
context.pending_list.reset(FALSE)<br>
context.remember_earlier_primary_start(nal)<br>
<font color="#a52a2a"><b>elif</b></font> nal.is_first_VCL_NAL(context.earlier_primary_start):<br>
<font color="#0000ff"># Regardless of what we determine next, we need to remember</font><br>
<font color="#0000ff"># that the NAL started (what may later be the previous) access</font><br>
<font color="#0000ff"># unit</font><br>
context.remember_earlier_primary_start(nal)<br>
<font color="#a52a2a"><b>if</b></font> access_unit.started_primary_picture:<br>
<font color="#0000ff"># We were already in an access unit with a primary</font><br>
<font color="#0000ff"># picture, so this NAL unit must start a new access unit.</font><br>
<font color="#0000ff"># Remember it for next time, and return the access unit so</font><br>
<font color="#0000ff"># far.</font><br>
context.pending_nal = nal<br>
<font color="#a52a2a"><b>break</b></font>; <font color="#0000ff"># Ready to return the access unit</font><br>
<font color="#a52a2a"><b>else</b></font>:<br>
<font color="#0000ff"># This access unit was waiting for its primary picture</font><br>
access_unit.append(nal,TRUE,context.pending_list)<br>
context.pending_list.reset(FALSE)<br>
<font color="#a52a2a"><b>elif</b></font> <font color="#a52a2a"><b>not</b></font> access_unit.started_primary_picture:<br>
<font color="#0000ff"># But this is not a NAL unit that may start a new</font><br>
<font color="#0000ff"># access unit. So what should we do? Ignore it?</font><br>
<font color="#a52a2a"><b>if</b></font> <font color="#a52a2a"><b>not</b></font> quiet:<br>
WARNING(<span style="background-color: #f2f2f2"><font color="#ff00ff">"!!! Ignoring VCL NAL that cannot start a new"</font></span><br>
<span style="background-color: #f2f2f2"><font color="#ff00ff">" primary picture: "</font></span><br>
nal.report(stderr)<br>
<font color="#a52a2a"><b>elif</b></font> nal_is_redundant(nal):<br>
<font color="#0000ff"># printf(" ignoring redundant NAL unit\n")</font><br>
<font color="#a52a2a"><b>pass</b></font><br>
<font color="#a52a2a"><b>else</b></font>:<br>
<font color="#0000ff"># We're part of the same access unit, but not special</font><br>
access_unit.append(nal,FALSE,context.pending_list)<br>
context.pending_list.reset(FALSE)<br>
<font color="#a52a2a"><b>elif</b></font> nal.nal_unit_type == NAL_ACCESS_UNIT_DELIM:<br>
<font color="#0000ff"># An access unit delimiter always starts a new access unit</font><br>
<font color="#a52a2a"><b>if</b></font> access_unit.started_primary_picture:<br>
context.pending_list.append(nal)<br>
<font color="#a52a2a"><b>break</b></font> <font color="#0000ff"># Ready to return the "previous" access unit</font><br>
<font color="#a52a2a"><b>else</b></font>:<br>
<font color="#0000ff"># The current access unit doesn't yet have any VCL NALs</font><br>
<font color="#a52a2a"><b>if</b></font> context.pending_list.length > <span style="background-color: #f2f2f2"><font color="#ff00ff">0</font></span>:<br>
WARNING(<span style="background-color: #f2f2f2"><font color="#ff00ff">"!!! Ignoring items after last VCL NAL and"</font></span><br>
<span style="background-color: #f2f2f2"><font color="#ff00ff">" before Access Unit Delimiter</font></span><span style="background-color: #f2f2f2"><font color="#6a5acd">\n</font></span><span style="background-color: #f2f2f2"><font color="#ff00ff">"</font></span>)<br>
context.pending_list.report(stderr,<span style="background-color: #f2f2f2"><font color="#ff00ff">" "</font></span>,NULL,)<br>
context.pending_list.reset(TRUE)<br>
<font color="#a52a2a"><b>if</b></font> access_unit.nal_units.length > <span style="background-color: #f2f2f2"><font color="#ff00ff">0</font></span>:<br>
WARNING(<span style="background-color: #f2f2f2"><font color="#ff00ff">"!!! Ignoring incomplete access unit</font></span><span style="background-color: #f2f2f2"><font color="#6a5acd">\n</font></span><span style="background-color: #f2f2f2"><font color="#ff00ff">"</font></span>)<br>
access_unit.nal_units.report(stderr,<span style="background-color: #f2f2f2"><font color="#ff00ff">" "</font></span>,NULL,)<br>
access_unit.nal_units.reset(TRUE)<br>
access_unit.append(nal,FALSE,NULL)<br>
<font color="#a52a2a"><b>elif</b></font> nal.nal_unit_type == NAL_SEI:<br>
<font color="#0000ff"># SEI units always precede the primary coded picture</font><br>
<font color="#0000ff"># - so they also implicitly end any access unit that has already</font><br>
<font color="#0000ff"># started its primary picture</font><br>
<font color="#a52a2a"><b>if</b></font> access_unit.started_primary_picture:<br>
context.pending_list.append(nal)<br>
<font color="#a52a2a"><b>break</b></font> <font color="#0000ff"># Ready to return the "previous" access unit</font><br>
<font color="#a52a2a"><b>else</b></font>:<br>
context.pending_list.append(nal)<br>
<font color="#a52a2a"><b>elif</b></font> nal.nal_unit_type <font color="#a52a2a"><b>in</b></font> [NAL_SEQ_PARAM_SET, NAL_PIC_PARAM_SET,<br>
<span style="background-color: #f2f2f2"><font color="#ff00ff">13</font></span>, <span style="background-color: #f2f2f2"><font color="#ff00ff">14</font></span>, <span style="background-color: #f2f2f2"><font color="#ff00ff">15</font></span>, <span style="background-color: #f2f2f2"><font color="#ff00ff">16</font></span>, <span style="background-color: #f2f2f2"><font color="#ff00ff">17</font></span>, <span style="background-color: #f2f2f2"><font color="#ff00ff">18</font></span>]:<br>
<font color="#0000ff"># These start a new access unit *if* they come after the last VCL</font><br>
<font color="#0000ff"># NAL of an access unit. But we can only *tell* that they are</font><br>
<font color="#0000ff"># after the last VCL NAL of an access unit when we start the next</font><br>
<font color="#0000ff"># access unit - so we need to hold them in hand until we know that</font><br>
<font color="#0000ff"># we need them. (i.e., they'll get added to an access unit just</font><br>
<font color="#0000ff"># before the next "more determined" NAL unit we add to an access</font><br>
<font color="#0000ff"># unit)</font><br>
context.pending_list.append(nal)<br>
<font color="#a52a2a"><b>elif</b></font> nal.nal_unit_type == NAL_END_OF_SEQ:<br>
<font color="#a52a2a"><b>if</b></font> context.pending_list.length > <span style="background-color: #f2f2f2"><font color="#ff00ff">0</font></span>:<br>
WARNING(<span style="background-color: #f2f2f2"><font color="#ff00ff">"!!! Ignoring items after last VCL NAL and"</font></span><br>
<span style="background-color: #f2f2f2"><font color="#ff00ff">" before End of Sequence</font></span><span style="background-color: #f2f2f2"><font color="#6a5acd">\n</font></span><span style="background-color: #f2f2f2"><font color="#ff00ff">"</font></span>)<br>
context.pending_list.report(stderr,<span style="background-color: #f2f2f2"><font color="#ff00ff">" "</font></span>,NULL,)<br>
context.pending_list.reset(TRUE)<br>
<font color="#0000ff"># And remember this as the End of Sequence marker</font><br>
context.end_of_sequence = nal<br>
<font color="#a52a2a"><b>break</b></font><br>
<font color="#a52a2a"><b>elif</b></font> nal.nal_unit_type == NAL_END_OF_STREAM:<br>
<font color="#0000ff"># And remember this as the End of Stream marker</font><br>
context.end_of_stream = nal<br>
<font color="#0000ff"># Which means there's no point in reading more from this stream</font><br>
<font color="#0000ff"># (setting no_more_data like this means that *next* time this</font><br>
<font color="#0000ff"># function is called, it will return EOF)</font><br>
context.no_more_data = TRUE<br>
<font color="#0000ff"># And we're done</font><br>
<font color="#a52a2a"><b>break</b></font><br>
<font color="#a52a2a"><b>else</b></font>:<br>
<font color="#0000ff"># It's not a slice, or an access unit delimiter, or an</font><br>
<font color="#0000ff"># end of sequence or stream, or a sequence or picture</font><br>
<font color="#0000ff"># parameter set, or various other odds and ends, so it</font><br>
<font color="#0000ff"># looks like we can ignore it.</font><br>
<font color="#a52a2a"><b>pass</b></font><br>
<br>
<font color="#0000ff"># Check for an immediate "end of file with no data"</font><br>
<font color="#0000ff"># - i.e., we read EOF or end of stream, and there was nothing</font><br>
<font color="#0000ff"># between the last access unit and such reading</font><br>
<font color="#a52a2a"><b>if</b></font> context.no_more_data <font color="#a52a2a"><b>and</b></font> access_unit.nal_units.length == <span style="background-color: #f2f2f2"><font color="#ff00ff">0</font></span>:<br>
<font color="#a52a2a"><b>raise</b></font> EOF<br>
<br>
<font color="#0000ff"># Otherwise, finish off and return the access unit we have in hand</font><br>
access_unit.end(context,show_details)<br>
<br>
<font color="#0000ff"># Remember to count it</font><br>
context.access_unit_index += <span style="background-color: #f2f2f2"><font color="#ff00ff">1</font></span><br>
<br>
<font color="#a52a2a"><b>return</b></font> access_unit<br>
</font></body>
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