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• Transcode HLS Segments individually using FFMPEG

  27 mai 2013, par rayh

  I am recording a continuous, live stream to a high-bitrate HLS stream. I then want to asynchronously transcode this to different formats/bitrates. I have this working, mostly, except audio artefacts are appearing between each segment (gaps and pops).

  Here is an example ffmpeg command line :

  ffmpeg -threads 1 -nostdin -loglevel verbose \
  
     -nostdin -y -i input.ts -c:a libfdk_aac \
  
     -ac 2 -b:a 64k -y -metadata -vn output.ts

  Inspecting an example sound file shows that there is a gap at the end of the audio :

  

  And the start of the file looks suspiciously attenuated (although this may not be an issue) :

  

  My suspicion is that these artefacts are happening because transcoding are occurring without the context of the stream as a whole.

  Any ideas on how to convince FFMPEG to produce audio that will fit back into a HLS stream ?

  ** UPDATE 1 **

  Here are the start/end of the original segment. As you can see, the start still appears the same, but the end is cleanly ended at 30s. I expect some degree of padding with lossy encoding, but I there is some way that HLS manages to do gapless playback (is this related to iTunes method with custom metadata ?)

  
  

  ** UPDATED 2 **

  So, I converted both the original (128k aac in MPEG2 TS) and the transcoded (64k aac in aac/adts container) to WAV and put the two side-by-side. This is the result :

  
  

  I'm not sure if this is representative of how a client will play it back, but it seems a bit odd that decoding the transcoded one introduces a gap at the start and makes the segment longer. Given they are both lossy encoding, I would have expected padding to be equally present in both (if at all).

  ** UPDATE 3 **

  According to http://en.wikipedia.org/wiki/Gapless_playback - Only a handful of encoders support gapless - for MP3, I've switched to lame in ffmpeg, and the problem, so far, appears to have gone.

  For AAC (see http://en.wikipedia.org/wiki/FAAC), I have tried libfaac (as opposed to libfdk_aac) and it also seems to produce gapless audio. However, the quality of the latter isn't that great and I'd rather use libfdk_aac is possible.

• Using moviepy, how can I splice up long videos into 8-second bits ?

  18 septembre 2020, par ekinugurel

  relatively new python user here. I'm trying to use moviepy to splice up 5 min long videos into 8-second bits. I used the code in this thread to extract subclips and it works. I did the following to make it a loop that covers the whole video, but I only get one 8-sec video as an output :

  


  from moviepy.video.io.ffmpeg_tools import ffmpeg_extract_subclip
videopath = '../img/videos/Mopac+Cesarchavez-1.m4v'

for sec in videopath:
    sec = 0
    ffmpeg_extract_subclip(videopath, sec, sec+8.00, "../img/videos/subclips/testclip.mp4")
    if sec == 327:
        break


  


  Do I need to specify a naming convention so that my output isn't just one video ? How would I do that ?

  


• avcodec/cbs_av1 : remove dead code

  12 novembre 2020, par James Almer

  avcodec/cbs_av1 : remove dead code
  The other branch already covers cases where enable_order_hint is true
  
  and frame is of type Inter.
  
  Regression since ddb0e4fecdef24e8c7b90fa0a41d13e642ea732f
  Fixes Coverity issues #1469194 and #1469195.
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavcodec/cbs_av1_syntax_template.c