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Hi,<br><br>Basically I am interested in using playbin to extract video packets from a media file. <br><br>I
have replaced the video decoder element in decodebin by a identity
element, to bypass the video decoding process. I also modified playbin
such that the colorspace, videoscale, and videosink are replaced by a
filesink, to save the extracted video packets into a file. I was able
to extract video packets and save them into a file. However, there are
two problems:<br>
<br>1. using an mpeg-4 video file (only contains video stream, and
encoded by ffmpeg) as the input, the output file size is smaller than
that of the input. I would expect they have the same file size since
the input only contains video stream (ffmpeg shows there is no muxing
overhead). And the output file is not decodable by neither gstreamer
nor ffplay. As another test, I use an avi file as the input. It has
both video and audio streams. Video is encoded in H.264. The output
file size is smaller than that of the input as expected. And
interestingly, the output file, which is basically an H.264 bitstream,
is decodable by ffplay, but not by gstreamer. My question is: could
this be a threading problem since the new "playback" is much faster
than normal decode + display process? And how to solve (or investigate)
this?<br>
<br>2. verbose output shows that the offset and offset_end of identity
element in decodebin seem to be wrong (shown below). Also it seems that
the "playback" already starts before "Setting pipeline to PLAYING". I
am not sure if this is normal since I know little about the lower level
threading within gstreamer.<br>
<br>partial verbose output for a mpeg-4 video sequence "playback" is shown here:<br>/GstPlayBin:playbin0/GstBin:<div id=":1s4" class="ii gt"><wbr>vbin.GstGhostPad:sink.<wbr>GstProxyPad:proxypad2: caps = video/mpeg, mpegversion=(int)4, systemstream=(boolean)false, codec_data=(buffer)<wbr>000001b001000001b5891300000100<wbr>0000012000c48d8800cd0b04241463<wbr>000001b24c61766335322e32302e30<wbr>, width=(int)352, height=(int)288, framerate=(fraction)25/1<br>
/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (1230 bytes,
timestamp: 0:00:00.320000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 256) 0x839ae30"<br>
/GstPlayBin:playbin0/GstBin:<wbr>vbin/GstFileSink:vfsink.<wbr>GstPad:sink: caps = video/mpeg, mpegversion=(int)4, systemstream=(boolean)false, codec_data=(buffer)<wbr>000001b001000001b5891300000100<wbr>0000012000c48d8800cd0b04241463<wbr>000001b24c61766335322e32302e30<wbr>, width=(int)352, height=(int)288, framerate=(fraction)25/1<br>
/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (1282 bytes,
timestamp: 0:00:00.360000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 256) 0x839ae80"<br>
Pipeline is PREROLLED ...<br>Setting pipeline to PLAYING ...<br>/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (1153 bytes,
timestamp: 0:00:00.400000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 256) 0x839aed0"<br>
/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (1287 bytes,
timestamp: 0:00:00.440000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 256) 0x83866f0"<br>
/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (16000 bytes,
timestamp: 0:00:00.480000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 0) 0x8386600"<br>
/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (1432 bytes,
timestamp: 0:00:00.520000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 256) 0x83865b0"<br>
New clock: GstSystemClock<br>/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (2095 bytes,
timestamp: 0:00:00.560000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 256) 0x8386560"<br>
/GstPlayBin:playbin0/<wbr>GstDecodeBin:decodebin0/<wbr>GstIdentity:identity0:
last-message = "chain ******* (identity0:sink)i (2781 bytes,
timestamp: 0:00:00.600000000, duration: 0:00:00.040000000, offset: -1,
offset_end: -1, flags: 256) 0x8386510"<br>
<br><br>I am quite new to gstreamer. Hopefully some experts can give me some hints. Thanks.<br><br>Regards,<br><font color="#888888"><br>Qin</font></div><br /><hr />把MSN装进手机，更多聊天乐趣等你挖掘！ <a href='http://mobile.msn.com.cn/' target='_new'>立刻下载！</a></body>
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