<div dir="ltr">Here are the correct links to the documents (which are viewable).<div><ul><li>avc1:
<a href="https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=6312">https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=6312</a> <br></li><li>avc3:
<a href="https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=7825" target="_blank">https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=7825</a></li></ul><div>The links come from <a href="https://en.wikipedia.org/wiki/Advanced_Video_Coding#Versions" target="_blank">https://en.wikipedia.org/wiki/Advanced_Video_Coding#Versions</a>.</div><div><br></div><div>In both documents, page 31 / section 7.3.2.1 defines the Sequence parameter set RBSP syntax, which includes:</div><ul><li>pic_width_in_mbs_minus1</li><li>pic_height_in_map_units_minus_1</li></ul><div>Therefore I believe avc1 allows for changes to width and height via SBS (sequence parameter set).</div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Dec 4, 2019 at 10:46 AM Mathieu Duponchelle <<a href="mailto:mathieu@centricular.com">mathieu@centricular.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
I'm afraid I don't have these documents available to me anymore
(pretty sure I got them at some point).<br>
Perhaps someone else will read this and lend you their copy :)<br>
<br>
<div>On 12/4/19 7:03 PM, David Ing wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Mathieu --
<div><br>
</div>
<div>Please excuse the inadequacy of my google-fu. I am having
trouble finding any kind of authoritative reference document
which describes avc1, 2, 3, 4, ... (and the subtle differences
between them)</div>
<div>
<ul>
<li>My best guess is that avc1 refers to the first
amendment: <a href="https://www.iso.org/standard/67318.html" target="_blank">https://www.iso.org/standard/67318.html</a></li>
<li>My best guess is that avc3 refers to the third
amendment: <a href="https://www.iso.org/standard/69728.html" target="_blank">https://www.iso.org/standard/69728.html</a></li>
</ul>
</div>
<div>Also -- I am a bit surprised that we need to pay in order
to view documents like this. Does anyone know if there is a
way to view this stuff for free?<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, Dec 4, 2019 at 9:14 AM
Mathieu Duponchelle <<a href="mailto:mathieu@centricular.com" target="_blank">mathieu@centricular.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div> That's an interesting file, but I'm not sure it is a a
compliant one: the resolution change is<br>
advertised through SPS in the bitstream, but the MP4 header
says "avc1", which as far as I remembe<br>
means the H264 bitstream should not contain any SPS (please
double check this, haven't looked at the spec).<br>
<br>
Ideally, the tool you produced this file with would use an
"avc3" stream format, and not hold<br>
any parameter sets in its MP4 header. That way, you could
detect resolution changes by simply<br>
plugging a demuxer and a parser together and looking for new
caps. Currently you can only do that<br>
either by also plugging a decoder afterwards and looking for
caps changes, or analysing the SPS<br>
manually :)<br>
<br>
Best,<br>
<br>
<div>-- <br>
Mathieu Duponchelle · <a href="https://www.centricular.com" target="_blank">https://www.centricular.com</a></div>
<br>
<br>
<div>On 12/3/19 10:50 PM, David Ing wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">I have an mp4 file which changes size
during playback. But I noticed that gst-discoverer-1.0
does not report the fact that the size changes.
<div><br>
</div>
<div><span style="background-color:rgb(255,255,0)">I
have two questions</span>.</div>
<div>
<ol>
<li>In theory, what is the fastest way to scan the
file to determine where the size changes?</li>
<li>In practice, what is the easiest way (given the
current state of gstreamer) to scan the file and
determine where the size changes?</li>
</ol>
<div>
<div>Here is the file which changes size during
playback:<br>
</div>
</div>
<div><br>
</div>
<blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px">
<div>
<div><a href="https://drive.google.com/drive/folders/1f4pGNDhzCvsg1xXWj4y9DS3vXkaglOvZ?usp=sharing" target="_blank">https://drive.google.com/drive/folders/1f4pGNDhzCvsg1xXWj4y9DS3vXkaglOvZ?usp=sharing</a></div>
</div>
<div><br>
</div>
</blockquote>
Here is the gst-discoverer-1.0 output:
<div><br>
</div>
<blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px">
<div><font face="monospace">$ <b>gst-discoverer-1.0
-v screencap.m4v </b></font></div>
<div><font face="monospace">Analyzing <a>file:///home/ding/mess/repro/screencap.m4v</a></font></div>
<div><font face="monospace">Done discovering <a>file:///home/ding/mess/repro/screencap.m4v</a></font></div>
<div><font face="monospace"><br>
</font></div>
<div><font face="monospace">Topology:</font></div>
<div><font face="monospace"> container:
video/quicktime, variant=(string)iso</font></div>
<div><font face="monospace"> video: video/x-h264,
stream-format=(string)avc, alignment=(string)au,
level=(string)4.2, profile=(string)main,
codec_data=(buffer)014d402affe1002b674d402a965402a835f35602d40404050000030001000003003ce060007d0000030177009a9503b4244d4001000468ce3520,
width=(int)996, height=(int)632,
pixel-aspect-ratio=(fraction)1/1,
framerate=(fraction)30/1,
interlace-mode=(string)progressive,
chroma-format=(string)4:2:0,
bit-depth-luma=(uint)8,
bit-depth-chroma=(uint)8, parsed=(boolean)true</font></div>
<div><font face="monospace"> Tags:</font></div>
<div><font face="monospace"> video codec:
H.264 / AVC</font></div>
<div><font face="monospace"> bitrate: 309812</font></div>
<div><font face="monospace"> datetime:
2019-11-01T17:40:33Z</font></div>
<div><font face="monospace"> title: n/a</font></div>
<div><font face="monospace"> container
format: ISO MP4/M4A</font></div>
<div><font face="monospace"> </font></div>
<div><font face="monospace"> Codec:</font></div>
<div><font face="monospace"> video/x-h264,
stream-format=(string)avc, alignment=(string)au,
level=(string)4.2, profile=(string)main,
codec_data=(buffer)014d402affe1002b674d402a965402a835f35602d40404050000030001000003003ce060007d0000030177009a9503b4244d4001000468ce3520,
width=(int)996, height=(int)632,
pixel-aspect-ratio=(fraction)1/1,
framerate=(fraction)30/1,
interlace-mode=(string)progressive,
chroma-format=(string)4:2:0,
bit-depth-luma=(uint)8,
bit-depth-chroma=(uint)8, parsed=(boolean)true</font></div>
<div><font face="monospace"> Additional info:</font></div>
<div><font face="monospace"> None</font></div>
<div><font face="monospace"> Stream ID:
14c5bd3783191c8af25f30b00a879f8f7bdaa4367c8ecbd954b38e5367507175/001</font></div>
<div><font face="monospace"> Width: 1350</font></div>
<div><font face="monospace"> Height: 846</font></div>
<div><font face="monospace"> Depth: 24</font></div>
<div><font face="monospace"> Frame rate: 30/1</font></div>
<div><font face="monospace"> Pixel aspect
ratio: 1/1</font></div>
<div><font face="monospace"> Interlaced: false</font></div>
<div><font face="monospace"> Bitrate: 309812</font></div>
<div><font face="monospace"> Max bitrate: 0</font></div>
<div><font face="monospace"><br>
</font></div>
<div><font face="monospace">Properties:</font></div>
<div><font face="monospace"> Duration:
0:00:34.861322222</font></div>
<div><font face="monospace"> Seekable: yes</font></div>
<div><font face="monospace"> Live: no</font></div>
<div><font face="monospace"> Tags: </font></div>
<div><font face="monospace"> video codec: H.264
/ AVC</font></div>
<div><font face="monospace"> bitrate: 309812</font></div>
<div><font face="monospace"> datetime:
2019-11-01T17:40:33Z</font></div>
<div><font face="monospace"> title: n/a</font></div>
<div><font face="monospace"> container format:
ISO MP4/M4A</font></div>
</blockquote>
</div>
</div>
<br>
<fieldset></fieldset>
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