<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>MP4 timing issue implementing a dash demux</TITLE> <META http-equiv=Content-Type content="text/html; charset=iso-8859-1"> <META content="MSHTML 6.00.6000.17063" name=GENERATOR></HEAD> <BODY> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2>Hi,</FONT></SPAN></DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2></FONT></SPAN> </DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2>After discussing with DASH experts, it appears that specific DASH boxes have been added to address this issue.</FONT></SPAN></DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2>The Track Fragment Decode Time (tfdt) seems in particular to be the place where the fragment offset is supposed to be specified.</FONT></SPAN></DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2>I have modified the qtdemux to parse it and add the result to the output timestamps, and it solves the playback issues.</FONT></SPAN></DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2></FONT></SPAN> </DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2>I have created a bug here: <A href="https://bugzilla.gnome.org/show_bug.cgi?id=677535"><FONT face="Times New Roman" size=3>https://bugzilla.gnome.org/show_bug.cgi?id=677535</FONT></A></FONT></SPAN></DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2></FONT></SPAN> </DIV> <DIV dir=ltr align=left><SPAN class=843200508-06062012><FONT face=Arial size=2>David</FONT> </SPAN></DIV><BR> <DIV class=OutlookMessageHeader lang=fr dir=ltr align=left> <HR tabIndex=-1> <FONT face=Tahoma size=2><B>De :</B> gstreamer-devel-bounces+david.corvoysier=orange.com@lists.freedesktop.org [mailto:gstreamer-devel-bounces+david.corvoysier=orange.com@lists.freedesktop.org] <B>De la part de</B> david.corvoysier@orange.com<BR><B>Envoyé :</B> mardi 29 mai 2012 17:08<BR><B>À :</B> gstreamer-devel@lists.freedesktop.org<BR><B>Cc :</B> sebastian.droege@collabora.co.uk<BR><B>Objet :</B> MP4 timing issue implementing a dash demux<BR></FONT><BR></DIV> <DIV></DIV> <P><FONT face=Arial size=2>Hi, </FONT></P> <P><FONT face=Arial size=2>Following Sebastian advice, we have implemented an MPEG DASH demux based on the HLS demux code.</FONT> <BR><FONT face=Arial size=2>Basically, the demux fetches the MP4 data fragments and pass them downstream.</FONT> <BR><FONT face=Arial size=2>Whenever a new bitrate is selected, a new output pad is created and decodebin2 creates the appropriate decoding chain.</FONT> <BR><FONT face=Arial size=2>In each new chain, decodebin2 instantiates in particular a new isomp4 demux, to which the DASH demux forwards an MP4 header (the initialization header), followed by as many MP4 data fragments.</FONT></P> <P><FONT face=Arial size=2>The DASH demux also sends a new segment event to specify the playback offset for that chain.</FONT> </P> <P><FONT face=Arial size=2>The issue we have is that the isomp4 demux ignores the new segment event and starts timestamping output buffers at 0.</FONT> <BR><FONT face=Arial size=2>This is harmless on some configurations where the video sink outputs frames in decoding order ignoring the timestamps, but on more restrictive configurations, it blocks playback until the new chain catches up with the playback time at which the previous one stopped (and as a nasty side effect, it rapidly drains our download queue, causing playback jerkiness).</FONT></P> <P><FONT face=Arial size=2>I am not sure how to handle this: should we force the new chain to seek up to the playback position it is supposed to start ? Should the offset rather be encoded in the MP4 enveloppe ? If so, would it even be parsed by the current isomp4 demux ?</FONT></P> <P><FONT face=Arial size=2>Thanks in advance for any explainations (I may have got it all wrong) and/or tips …</FONT> </P> <P><FONT face=Arial size=2>David Corvoysier</FONT> <BR><FONT face=Arial size=2>Orange Labs </FONT></P></BODY></HTML>