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• Why do I get different codecs on Windows and Linux with same code ?

  27 janvier 2016, par user3277340

  I am using the API version of FFMPEG to generate a MP4 file from a series of images. I specify the output by calling

  AVFormatContext *oc = NULL ;
  avformat_alloc_output_context2 (&oc,NULL,"mp4",NULL) ;

  Running the exact same code on Windows and Linux I get different codecs assigned. On Windows, the value of oc->oformat->video_code is AV_CODEC_ID_H264 (28), but on Linux I get AV_CODEC_ID_MPEG4.

  I tracked this down because on Windows my calls to avcodec_encode_video2(.,.,.,&got_packet) were always returning got_packet=0 so I never called av_interleaved_write_frame. I added a NULL AVFrame at the end to flush the video. But it was very small and did not contain the images I expected to see there.

  But on Linux everything worked just fine. So I went ahead and manually changed the value of oc->oformat->video_code and I got the expected results.

  My questions :

  1) Why do I get different codec types on different platforms with the same code ? Is there a parameter I need to set to force MPEG4 ?

  2) Is it "legal" to change this parameter after the call to avformat_alloc_output_context2 ? My concern is that "oc" has been properly initialized and, with the change, something may be inconsistent.

  3) Is there a way to force the MPEG4 codec on any machine ?

  Thanks.

• ffmpeg output in Audacity

  9 mai 2018, par siamak

  I wanted to split the audio track of a mp4 file each receiving different filter then merge to an output mp4 file. Please note I do not wanted series filter but rather parallel filter and then merge.

  I came up with the following command.
  ffmpeg -i input.mp4 -filter_complex "[0:a]asplit[audio1][audio2];[audio1]highpass=f=200:p=1:t=h:w=50;[audio2]lowpass=f=700:p=1:t=h:w=200;[audio1][audio2]amerge=inputs=2[out]" -map "[out]" -map 0:v -c:v copy -map 0:s? -c:s copy -ac 2 -y output.mp4

  this output will play on Vlc and mpv. However, when I try to open it in Audacity, I get :
  
  Why I do get this ? I assume the index[05] is the correct audio output.
  This raise the question, which audio track is playing when opened in Vlc ? How can I create an output which has only one final audio track ?

• aacenc : add support for coding of IS spectral coefficients

  2 juillet 2015, par Rostislav Pehlivanov

  aacenc : add support for coding of IS spectral coefficients
  This commit adds support for the coding of intensity stereo spectral
  
  coefficients. It also fixes the Mid/Side coding of band_types higher
  
  than RESERVED_BT (M/S must not be applied to their spectral coefficients,
  
  but marking M/S as present in encode_ms_info() is okay). Much
  
  of the changes here were taken from the decoder and inverted.
  
  This commit does not change the functionality of the decoder as the
  
  previous patch in this series zeroes ms_mask and is_mask.
  Reviewed-by : Claudio Freire <klaussfreire@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/aacenc.c