[gst-devel] faac does not seem to respect bitrate

[LRN]

On 29.01.2010 15:06, Francis Rammeloo wrote:
> It seems that faac does not always the requested respect bitrates. I
> have tested this on my Windows machine (using the WinBuilds) by
> converting a 128kbps mp3 to several mp4 files with different bitrates:
>
> gst-launch-0.10 filesrc location=kylie.mp3 ! decodebin2 ! faac
> bitrate=16000 ! mp4mux ! filesink location=16.mp4
>
> gst-launch-0.10 filesrc location=kylie.mp3 ! decodebin2 ! faac
> bitrate=32000 ! mp4mux ! filesink location=32.mp4
>
> gst-launch-0.10 filesrc location=kylie.mp3 ! decodebin2 ! faac
> bitrate=64000 ! mp4mux ! filesink location=64.mp4
>
> gst-launch-0.10 filesrc location=kylie.mp3 ! decodebin2 ! faac
> bitrate=128000 ! mp4mux ! filesink location=128.mp4
>
> gst-launch-0.10 filesrc location=kylie.mp3 ! decodebin2 ! faac
> bitrate=256000 ! mp4mux ! filesink location=256.mp4
>
> gst-launch-0.10 filesrc location=kylie.mp3 ! decodebin2 ! faac
> bitrate=320000 ! mp4mux ! filesink location=320.mp4
>
>
> The resulting filesizes show the issue:
>
> 29/01/2010  12:57    <DIR>          .
> 29/01/2010  12:57    <DIR>          ..
> 29/01/2010  12:55         4.402.912 32.mp4
> 29/01/2010  11:57         5.071.153 kylie.mp3
> 29/01/2010  12:58         4.403.427 64.mp4
> 29/01/2010  12:59         5.164.493 128.mp4
> 29/01/2010  12:59         8.918.765 256.mp4
> 29/01/2010  13:00         8.918.881 320.mp4
> 29/01/2010  13:01         4.402.803 16.mp4
>
>
> Is there a way to make it respect the requested bitrates?
>   
Try encoding kylie.mp3 with 1,2,3,4,5,6,7,8,9...318,319,320 kbps (you'll
need a batch file or a special shell command), then look at the file
sizes (sorted by bitrate you've used). My prediction is that you'll see
that filesize(bitrate) function is monotonely rising, but will do that
by leaping at some points instead of raising steadily.