Audio stream sounds very bad after video conversion to mp4

[Krakapuk]

Hi !
First of all, thanks a lot for this very helpful app !
I noticed that sound quality of the audio stream was very low after a video conversion to mp4 format.
It seems that's not the case using other video conversion formats: I tested conversions to .mpg .wmv and ogv and the audio stream quality was OK. So the problem seems specific to mp4 conversion.

Using ubuntu 12.04 LTS 64bits and Format Junkie 1.05

Thank you

[Alex Solanos (hakermania)]

Hello Krakapuk! Thanks for your interest!

Please specify what was the source format.

[Krakapuk (krakapuk)]

Sorry...
Details are :
I attached the Preferences.conf file that i use in Format junkie for these video conversion

I tested with 2 different source formats with the same results :

First source format is .avi file with those characteristics
   Video:
      Size 640 x 480
      Format XVID MPEG-4
      fps 25.000
  Audio:
      Format MPEG 1 Audio, Layer 3 (MP3)
      Bitrate 127 kbps
      Sample rate 44100 Hz
      Audio channel 2

After conversion using mp4:
   Video:
      Size 320 x 240
      Format MPEG-4 video
      fps 25.000
  Audio:
      Format AAC
      Bitrate 3 kbps (??? seems to correlate with the low quality of the audio stream)
      Sample rate 44100 Hz
      Audio channel 2

Same source file after conversion using mpg :
   Video:
      Size 320 x 240
      Format MPEG 1 Video
      fps 25.000
  Audio:
      Format MPEG 1 Audio, Layer 2
      Bitrate 128 kbps (Indeed audio stream is OK)
      Sample rate 44100 Hz
      Audio channel 2

Same source file after conversion using wmv :
   Video:
      Size 320 x 240
      Format Microsoft MPEG-4 4.3
      fps 25.000
  Audio:
      Format MPEG 1 Audio, Layer 2
      Bitrate 127 kbps (Indeed audio stream is OK)
      Sample rate 44100 Hz
      Audio channel 2

Second source format is .mkv file with those characteristics
   Video:
      Size 640 x 480
      Format On2 VP8
      fps 1000 (sounds weird but that's the result of file properties using nautilus)
  Audio:
      Format Vorbis
      Bitrate 128 kbps
      Sample rate 44100 Hz
      Audio channel 2

After conversion using mp4:
   Video:
      Size 320 x 240
      Format MPEG-4 video
      fps 25.000
  Audio:
      Format AAC
      Bitrate 22 kbps (??? seems also to correlate with the low quality of the audio stream)
      Sample rate 44100 Hz
      Audio channel 2

After conversion using mpg :
   Video:
      Size 320 x 240
      Format MPEG 1 Video
      fps 25.000
  Audio:
      Format MPEG 1 Audio, Layer 2
      Bitrate 127 kbps (Indeed audio stream is OK)
      Sample rate 44100 Hz
      Audio channel 2

After conversion using wmv :
   Video:
      Size 320 x 240
      Format Microsoft MPEG-4 4.3
      fps 25.000
  Audio:
      Format MPEG 1 Audio, Layer 2
      Bitrate 127 kbps (Indeed audio stream is OK)
      Sample rate 44100 Hz
      Audio channel 2

I hope this will be useful. Do not hesitate if you need more information.