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Having tested this further I realised that the H264VideoStreamFramer
assumes a constant 25fps. On a heavily loaded system which was
dropping frames this caused the timestamps to lose sync with wall
clock time so I'm still looking for a solution. <br>
<br>
Hopefully I can subclass the H264VideoStreamFramer to handle
discrete frame input in Annex B format somehow.<br>
<br>
<br>
<div class="moz-cite-prefix">On 03/11/2015 01:54 PM, Robert Smith
wrote:<br>
</div>
<blockquote cite="mid:55003B12.2060701@cognitec.com" type="cite">
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I've got this working now, I think my problem was conceptually
treating the byte stream as a series of frames instead of as a
continuous stream.<br>
<br>
Having looked at the ByteStreamMemoryBufferSource class it makes a
lot more sense now.<br>
<br>
<div class="moz-cite-prefix">On 03/11/2015 10:10 AM, Robert Smith
wrote:<br>
</div>
<blockquote cite="mid:55000684.3060003@cognitec.com" type="cite">
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Firstly apologies for the multiple posts.<br>
<br>
The platform is a TI DaVinci DM8148 using TI's HDVICP2 video
encoder hardware. As far as I can tell the encoder is capable of
outputting discrete NALU's but we are only able to use the
encoder via an OpenMAX API which doesn't expose this behaviour..
it's frustrating!.<br>
<br>
The encoder provides discrete 'frames' which consist of a buffer
of concatenated NALU's prepended with the start codes.<br>
<br>
Now that I think about it, If the H264VideoFramer is expecting
to read X bytes from a continuous stream, I should be able to
give it only part of the 'frame' that I receive from the
encoder? I'll try this and see how it works.<br>
<br>
Btw, On our other systems we use the Intel IPP H264 encoder and
the Intel Media SDK encoder, I'm not as familiar with them but I
understand that they also don't output discrete NALU's so I
thought this was common amongst encoders.<br>
<br>
<br>
Regarding slices, I can configure the encoder to encode a frame
as multiple slices based either on a maximum slice size or
number of MB's per slice but we're using GStreamer as one of our
clients and I get a lot of image corruption with multiple slices
enabled.<br>
<br>
I haven't had time to look into the problem deeper but using a
single slice was a quick and easy solution.<br>
<br>
Thanks,<br>
<br>
Robert Smith.<br>
<br>
<div class="moz-cite-prefix">On 03/10/2015 01:49 AM, Ross
Finlayson wrote:<br>
</div>
<blockquote
cite="mid:C3686A3F-6D98-4502-BBD8-C8BE762C3C0F@live555.com"
type="cite">
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<blockquote type="cite" class="">
<div class="">The encoder unfortunately only supplies
frames in Annex B byte stream format requiring the
frames to be parsed.</div>
</blockquote>
<div><br class="">
</div>
Are you sure about this? (Often, hardware encoders have
firmware upgrades available.)</div>
<div><br class="">
</div>
<div><br class="">
<blockquote type="cite" class="">
<div class=""> Previously I was using my own class to
identify the NAL unit's in conjunction with the
H264VideoDiscreteFramer which worked fine but it's heavy
on the CPU. So I've been trying to use the
H264VideoFramer and just pass the full frames in which
works ok and is faster than my solution except that I'm
seeing a lot of truncated frames.<br class="">
<br class="">
Having looked into the code it appears to be caused by
the behaviour of the StreamParser class; specifically
the ensureValidBytes1() method which calls
getNextFrame() on my source with maxSize = BANK_SIZE -
fTotNumValidBytes. The method switches banks to ensure
that the larger of numBytesNeeded or the input sources
maxFrameSize() will fit.<br class="">
<br class="">
I can 'fix' the problem by increasing BANK_SIZE and
implementing maxFrameSize() on my source but I'm not
totally happy with this solution because I would prefer
not to modify the library source and I'm just guessing
for the maxFrameSize() value.<br class="">
<br class="">
I was wondering whether it's possible to return a
partial frame from my video source?</div>
</blockquote>
<div><br class="">
</div>
Yes, but not in the way that you might think :-) A H.264
encoder actually delivers “NAL units”. “NAL units” are what
actually get parsed by our code, and packed into RTP
packets.</div>
<div><br class="">
</div>
<div>Often, a “NAL unit” is a complete frame. It is possible,
however, for a ‘key frame’ to be split up - by your encoder
- into multiple ‘slice’ NAL units. For datagram streaming
(e.g., over RTP), it is *much* better to have your key
frames broken up into multiple ‘slice’ NAL units, than to
have the key frame be a single, large NAL unit - which is
what you have now. This is especially true if your key
frames are exceptionally large: ~150000 bytes or larger,
which appears to be the case for you, because you are
hitting the BANK_SIZE limit (which was deliberately set to
be larger than realistically needed).</div>
<div><br class="">
</div>
<div>Note that a 150000 byte key frame NAL unit will get
transmitted as more than 1000 RTP packets (datagrams). (Our
code automatically handles the required fragmentation.) If
*any* of these 1000 packets gets lost in transit, then the
entire key frame will be undeliverable.</div>
<div><br class="">
</div>
<div>If, instead, your encoder delivers each key frame as
multiple ‘slice’ NAL units, then your streaming will be much
more resilient to network packet loss.</div>
<div><br class="">
</div>
<div>So, your first task should be to check whether your
encoder:</div>
<div>1/ can be reconfigured to deliver discrete frames, rather
than a stream with each NAL unit prepended by a 0x00 0x00
0x00 0x01 ‘start code’, and</div>
<div>2/ can be reconfigured to deliver key frames as multiple
‘slice’ NAL units, rather than as a single (ridiculously
large) NAL unit.</div>
<br class="">
<br class="">
<div apple-content-edited="true" class=""> <span
class="Apple-style-span" style="border-collapse: separate;
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style="border-collapse: separate; color: rgb(0, 0, 0);
font-family: Helvetica; font-style: normal;
font-variant: normal; font-weight: normal;
letter-spacing: normal; line-height: normal; orphans: 2;
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text-transform: none; white-space: normal; widows: 2;
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0px; -webkit-border-vertical-spacing: 0px;
-webkit-text-decorations-in-effect: none;
-webkit-text-size-adjust: auto;
-webkit-text-stroke-width: 0px; ">Ross Finlayson<br
class="">
Live Networks, Inc.<br class="">
<a moz-do-not-send="true" href="http://www.live555.com/"
class="">http://www.live555.com/</a></span></span> </div>
<br class="">
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