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• MLT melt slideshow on Windows: unable to control output video length and problems with using wildcards

  10 November 2020, by Tjk

  I am using the following command within a batch script to, hopefully, eventually programmatically create simple video slideshows with transitions:

  


  melt 131.jpg 132.jpg 133.jpg ttl=75 -attach crop center=1 -filter luma cycle=75 duration=25 -transition mix -consumer avformat:out.mp4 frame_rate_num=30 frame_rate_den=1


  


  Most of this command is an adaptation for Windows of this command on the MLT website blog (with the exception of the part that scales and transforms the image). For some reason when I run this, however, the output video file is 25 minutes long!

  


  I have two main questions:

  


  a. How do I properly control the duration of each image in the video? I have experimented quite a bit with changing the parameters and I have a semi-decent understanding of what they all mean (I am a newbie to MLT but I figured that there's no way to do something like this easily in FFMPEG alone). The only way I have found to decrease the duration with any amount of control is to increase the output framerate to absurd numbers (which, of course, is not ideal as it's a massive waste of time and energy and still doesn't really solve the issue).

  


  b. How do I use a wildcard to input all the .jpg files in a folder on Windows? I tried adding *.jpg but that didn't work and I don't know how else to do it within a batch script (I tried using the following code to get the file names as a variable, but I wasn't able to get string concatenation working correctly because it only outputs the final file name)

  


  set files=
for /r %%i in (*.jpg) do (
    echo %%i
    set files=%files% "%%i"
)
echo %files%


  


  Thank you for any suggestions!

  


• avcodec/aacenc: add strict bit rate control option

  25 April 2023, by Jeremy Wu

  avcodec/aacenc: add strict bit rate control option
  In certain use cases, controlling the maximum frame size is critical. An
  
  example is when transmitting AAC packets over Bluetooth A2DP.
  While the spec allows the packets to be fragmented (but UNRECOMMENDED),
  
  in practice most headsets do not recognize nor reassemble such packets.
  In this patch, we allow setting `bit_rate_tolerance` to 0 to indicate
  
  that the specified bit rate should be treated as an upper bound up to
  
  frame level.
  Signed-off-by: Jeremy Wu <jrwu@chromium.org>
  

  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/options_table.h

• FFmpeg avcodec_find_encoder problem

  13 November 2012, by net

  I'm newbie in ffmpeg.

  my problem is "avcodec_find_encoder(CODEC_ID_H264);" func always returning null.

  ffmpeg configure is below on my ubuntu system.

  ./ffmpeg
  
  FFmpeg version SVN-r26306, Copyright (c) 2000-2011 the FFmpeg developers
  
    built on Jan 11 2011 10:34:49 with gcc 4.4.5
  
    configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-postproc --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-x11grab
  
    libavutil     50.36. 0 / 50.36. 0
  
    libavcore      0.16. 0 /  0.16. 0
  
    libavcodec    52.108. 0 / 52.108. 0
  
    libavformat   52.92. 0 / 52.92. 0
  
    libavdevice   52. 2. 3 / 52. 2. 3
  
    libavfilter    1.72. 0 /  1.72. 0
  
    libswscale     0.12. 0 /  0.12. 0
  
    libpostproc   51. 2. 0 / 51. 2. 0

  as you can see, configuration contains —enable-libx264

  so I think avcodec_find_encoder(CODEC_ID_H264); have to return something not null...
  please let me know how to solve this problem?

  ps) I call avcodec_init() and av_register_all() in my program.

  when I compile my test program, using below

  gcc -o test test.c -lavutil -lavformat -lavcodec -lx264 -lz -lm

  thanks