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• Decoding AAC to PCM with ffmpeg results in noise

  18 October 2022, by userDtrm

  I have a .mp4 file generated with ffmpeg as follows.

  


  


  ffmpeg -y -i video_extended.mp4 -itsoffset 00:00:04.00 -i output5-1.wav -map 0:0 -map 1:0 -c:v copy -c:a aac -ac 6 -ar 48000 -b:a 128k -async 1 mixed.mp4

  


  


  Playing mixed.mp4 file with ffplay is fine and there is no impact to the sound quality. Below is the output I get from ffplay when using the command ffplay -i  mixed.mp4

  


  > Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
> 'mixed_h264_aac_512k_async_qp0_all_I.mp4':   Metadata:
>     major_brand     : isom
>     minor_version   : 512
>     compatible_brands: isomiso2avc1mp41
>     encoder         : Lavf58.76.100   Duration: 00:00:16.02, start: 0.000000, bitrate: 49136 kb/s   Stream #0:0[0x1](und): Video: h264 (High 4:4:4 Predictive) (avc1 / 0x31637661), yuv422p10le(progressive),
> 1920x1080, 65409 kb/s, 59.94 fps, 59.94 tbr, 11988 tbn (default)
>     Metadata:
>       handler_name    : VideoHandler
>       vendor_id       : [0][0][0][0]   Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 71 kb/s (default)
>     Metadata:
>       handler_name    : SoundHandler
>       vendor_id       : [0][0][0][0] Switch subtitle stream from #-1 to #-1 vq= 1606KB sq=    0B f=0/0


  


  Then, I decode the mixed.mp4 file back to raw PCM using the following command.

  


  


  ffmpeg -i mixed.mp4 -vn -acodec pcm_s16le -f s16le -ar 48000 -ac 6 raw_audio.pcm

  


  


  However, this raw_audio.pcm contains a lot of noise and ffplay output shows the following output

  


  [s16le @ 0x7f7490000c80] Estimating duration from bitrate, this may be inaccurate
Input #0, s16le, from 'separated_audio_s16.pcm':
  Duration: 00:00:16.02, bitrate: 4607 kb/s
  Stream #0:0: Audio: pcm_s16le, 48000 Hz, 6 channels, s16, 4608 kb/s
[pcm_s16le @ 0x7f749002b940] Multiple frames in a packet.
[pcm_s16le @ 0x7f749002b940] Invalid PCM packet, data has size 8 but at least a size of 12 was expected
    Last message repeated 32 times
[pcm_s16le @ 0x7f749002b940] Invalid PCM packet, data has size 8 but at least a size of 12 was expected
    Last message repeated 11 times
Switch subtitle stream from #-1 to #-1 vq=    0KB sq=    0B f=0/0   
[pcm_s16le @ 0x7f749002b940] Invalid PCM packet, data has size 8 but at least a size of 12 was expected
    Last message repeated 11 times
[pcm_s16le @ 0x7f749002b940] Invalid PCM packet, data has size 8 but at least a size of 12 was expected
    Last message repeated 11 times
[pcm_s16le @ 0x7f749002b940] Invalid PCM packet, data has size 8 but at least a size of 12 was expected


  


  Can someone please explain the issue here? Note that the ffplay command that works correctly for mixed.mp4 shows fltp as the audio format, whereas when playing the raw_audio.pcm file, it is seen as s16.

  


  Is this a resampling issue in ffmpeg, and how can I rectify this?

  


  I’m using ffmpeg and ffplay versions 5.0.1 in a Fedora 36 system.

  


  Thank you.

  


• webm files created with ffmpeg are too long

  6 August 2022, by Azrael

  I have a folder of exactly 300 images in png format (labelled 1.png, 2.png, ..., 300.png), which I'm trying to convert to a video. I would like the video to be in the webm format, but there seems to be an issue:

  


  using the following command:

  


  ffmpeg -start_number 1 -i ./frames/%d.png -frames:v 300 -r 30 out.webm


  


  does generate an out.webm file, and, according to ffprobe -select_streams v -count_frames -show_entries stream=nb_read_frames,r_frame_rate out.webm (which is presumably quite an inefficient way to get that information, but that's besides the point), it does contain 300 frames and has a framerate of exactly 30/1, however, instead of the expected exactly 10 seconds (from 300 frames being played at 30 fps), the video lasts slightly longer (about 12 seconds).
  
This discrepancy does seem to scale up with video length; 900 frames being converted to a video the same way and with the same frame rate yield a 36 (instead of 30) second video.

  


  For testing, I also tried generating an mp4 file instead of a webm one, with the following command (exact same as above, but out.mp4 instead of out.webm), and that worked exactly as expected, out.mp4 was a 10-second long video.

  


  ffmpeg -start_number 1 -i ./frames/%d.png -frames:v 100 -r 30 out.mp4


  


  How do I fix this? is my ffmpeg command off or is this a bug within the tool?

  


• Documentation #2846: blocage des notification à cause d’une protection .htaccess

  3 May 2013, by cedric -

  Je lis que l’on peut faire quelque chose comme
  

  SetEnvIf Request_URI ^spip.php\?action=cron$ bypass=1
  Satisfy any
  Order allow,deny
  
  Allow from env=bypass
  AuthUserFile ...
  
  AuthName ...
  
  AuthType Basic
  
  Require valid-user
  

  A tester