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• Will ffmpeg transcoding change the media's duration ?

  6 juillet 2012, par MaiTiano

  For example, I have a example flv media : 1775818137_1775828481_10344.flv. Only audio data has contained in it. (No video data)

  The major properties of this flv are :

  _____________________________________________________________________
  
  Format                                   : Flash Video
  
  
  
  File size                                : 87.4 KiB
  
  
  
  Duration                                 : 494 hours
  
  
  
  Overall bit rate mode                    : CBR
  
  
  
  Overall bit rate                         : 0 bps
  
  
  
  Writing application                      : Lavf53.4.0
  
  
  
  Audio
  
  
  
  Format                                   : MPEG Audio
  
  
  
  Format version                           : Version 1
  
  
  
  Format profile                           : Layer 3
  
  
  
  Mode                                     : Joint stereo
  
  
  
  Mode extension                           : MS Stereo
  
  
  
  Codec ID                                 : 2
  
  
  
  Codec ID/Hint                            : MP3
  
  
  
  Duration                                 : 49hours
  
  
  
  Bit rate mode                            : CBR
  
  
  
  Bit rate                                 : 64.0 Kbps
  
  
  
  Channel(s)                               : 2 channels
  
  
  
  Sampling rate                            : 44.1 KHz
  
  
  
  Compression mode                         : Lossy
  
  
  
  Stream size                              : 13.3 GiB
  
  
  
  _____________________________________________________________________

  Because this is the flv piece generated from the Suse10.0 server, the timestamp may be not correctly wrote into the flv metadata. Therefore, the Duration item listed above is not the real time of it.
  I has record the time in its file name.
  So, the beginning time is 1775818137 ms
  the ending time of this flv is 1775828481 ms
  The actual duation of this flv is 10344 ms which is about 10 seconds.

  **HERE IS MY QUESTION -.- **

  When I use ffmpeg to transcode flv fromat into ts format, like this,

  ./ffmpeg -i 1775818137_1775828481_10344.flv -f mpegts -vn -acodec libfaac -ar 44100 -ab 48k 1775818137_1775828481_10344.ts

  Is there possibility that the duration of final gotten ts file is not equal to the duation of original flv file ? In other words, the ts file's duration is not 10344ms.

• Size Discrepany in the ‘du’ Command

  22 juin 2012, par Multimedia Mike — General

  I had a problem today while using the common Unix command ’du’. As a refresher, ’du’ stands for disk usage and is a handy tool for understanding how much disk space is being occupied.

  I think ’du’ is probably doing the right thing. The problem might be that I’m getting strange (read : 1/2 the expected number) when running the tool against directories on vmhgfs, the VMware filesystem.

  Science Project
  On an Ubuntu Linux VMware session, my home directory is on the main file system, which is ext4. The directory /mnt/hgfs is reported by ’mount’ to be of type vmhgfs and is shared with the host machine.

  Create a directory in the home directory and generate a 10 MiB file :

  mkdir /home/melanson/dir
  dd if=/dev/urandom of=/home/melanson/dir/random-file bs=1048576 count=10
  

  Create a directory on the shared drive and copy the same file :

  mkdir /mnt/hgfs/vmshare/dir
  cp /home/melanson/dir/random-file /mnt/hgfs/vmshare/dir
  

  Run ’du’ on each directory using the -k and -h options :

  du -k /home/melanson/dir /mnt/hgfs/vmshare/dir
  10244   /home/melanson/dir
  5120    /mnt/hgfs/vmshare/dir
  du -h /home/melanson/dir /mnt/hgfs/vmshare/dir
  
  11M    /home/melanson/directory
  
  5.0M   /mnt/hgfs/vmshare/directory
  

  I noticed this discrepancy when I was trying to pack a set of files (akin to ’tar’-ing) living in a directory in the shared location. I was going mad trying to understand why the original directory was only 2 MB as reported by ’du’ but the final packed file was 4 MB.

  To be fair, the man page for ’du’ succinctly states that the tool’s purpose is merely to "estimate file space usage".

• FFmpeg X264 multithread decoding

  16 novembre 2013, par Xin He

  I want to do H264 multithread decoding using FFmpeg.
  First I use X264 to encode yuv420 to file.x264
  ./x264 -o file.x264 —slices 4 —input-res 1280x720 —fps 25 file_560x420.yuv

  The slices count is 4.

  However, when I use FFmpeg to decode,
  ./ffmpeg -y -threads 4 -thread_type slice -i file.x264 final.yuv

  FFmpeg calls func"execute_decode_slices" four times, not in a multithread way.
  I also found that in *execute_decode_slices(h, context_count)*, the context_count is 1.
  FFmpeg call this 4 times.

  Could someone help to solve this problem ?

  Thanks very much !