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• Revision 28930 : on bouge

  31 mai 2009, par ben.spip@… — Log

  on bouge

• mp4 And Rotation - Remove Flags But Set Rotation

  7 avril 2024, par Bud

  I'm having a hard time with the rotation on some mp4 files I have. It may well be my poor understanding, so forgive me if I set out what I know (or think I know) and then what I want to happen.

  


  An mp4 has, obviously, a right way up - that is, the way you want it to show when you watch it. Call this the orientation. This isn't metadata - it's just the way you, as a person, want to see the image, with people's heads at the top of the screen and their feet at the bottom.

  


  As part of the metadata, mp4 files have a value/parameter (I believe called 'rotate') that tells how much the mp4 needs to be rotated (0, 90, 180, 270 degrees) so that it is correctly oriented. This value/parameter is observed by some players and not by some others. So if I play my video using this player, all is good (because it observes the value/parameter) - but if I play it with that other player, everything is sideways (because it doesn't observe the value/parameter).

  


  What I want to do is orient the mp4 correctly with the value/parameter set to 0, so that no matter what player plays it, it will always be played oriented correctly (because those players that observe the value/parameter will see it's 0 and do nothing). So I think what I need to do is somehow remove the value/parameter, then rotate the mp4 to the correct orientation without using the rotate value/parameter. I'm thinking of something like what FastStone Image Viewer can do with JPGs - rotate them losslessly without setting the rotate value.

  


  I've used ffmpeg and believe that it removed the rotate value/parameter (or set it to 0) because after I used it, suddenly my video appeared sideways in Windows Explorer, where previously it had appeared right way up. But how do I now rotate it to the correct orientation without changing the rotate value/parameter ?

  


  Sorry, this is very long winded and confused. Just like me.

  


• Start Android Java VM from native C code NDK (ffmpeg mediacodec use)

  19 avril 2021, par eusoubrasileiro

  I managed to cross-compile ffmpeg using the NDK for armv8a api 27 with MediaCodec hardware acceleration support.

  


  Using root after setting permissions, folders and setting properly LD_LIBRARY_PATH etc. I can run it without problems on a terminal session (ssh). Only if I don't try to use the -hwaccel option.

  


  If try to run something using -hwaccel, like :

  


  ffmpeg -rtsp_transport tcp -an -hwaccel mediacodec -c:v hevc_mediacodec -i rtsp://user:pass@192.168.0.100:554/onvif1 -f null - -benchmark


  


  I get the error bellow about No Java virtual machine.

  


  ...
Input #0, rtsp, from 'rtsp://user:pass@192.168.0.100:554/onvif1':
  Metadata:
    title           : H.265 Video, RtspServer_0.0.0.2
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: hevc (Main), yuv420p(tv, bt470bg), 1920x1080 [SAR 1:1 DAR 16:9], 10 fps, 10 tbr, 90k tbn, 10 tbc
    Stream #0:1: Audio: pcm_alaw, 8000 Hz, mono, s16, 64 kb/s
[amediaformat @ 0x7e2ea27300] No Java virtual machine has been registered
[hevc_mediacodec @ 0x7e2eb44f00] Failed to create media format
Stream mapping:
  Stream #0:0 -> #0:0 (hevc (hevc_mediacodec) -> wrapped_avframe (native))
Error while opening decoder for input stream #0:0 : Generic error in an external library


  


  Would it be possible to start (create or launch ?) the Dalvik Java VM directly from the C code ? I don't even know if those are correct terms. Make it visible for ffmpeg ?

  


  Any information that will help a Android Newbie get on his feet will be greatly appreciated. If that is possible I would write a little patch on the ffmpeg code.

  


  I really would not like to package this in an app only to be able to test around with this.