audio data rate when transcoding

[ski]

I am transcoding some video files with audio using the command line on windows. VLC version 0.84a. I always get the same audio bit rate (about 80kbps) no matter what bit rate I specify with the ab setting. Here are my settings:

"C:\Program Files\VideoLAN\VLC\vlc.exe" ".\synthetic1 qvga 30fps.avi" --sout=#transcode{vcodec=h264,vb=300,acodec=mp4a,ab=48,channels=2}:duplicate{dst=std{access=file,mux=mp4,url="..\h264 mp4 compressed files\synthetic1 300-48 test.mp4"}} vlc:quit

Any ideas? Thanks.

[DJ]

It is possible that the developer for this module put caps on the limits knowing that the format could not handle the bit rate.

What are you using to judge this?

[ski]

I use quicktime to identify the audio rate and simple math using the file size, duration, and video content data to double-check. It looks like I'm getting a default rate when transcoding to AAC audio using VLC. I'm hoping that I have a setting wrong somewhere.

[DJ]

acodec=mp4a,ab=48,channels=2

You are asking for 48k bitrate this is not samplerate as such would be considered extremely low for this format.

[ski]

I don't know why you think 48kbps is low for AAC. It is the rate typically used for video on mobile phones (Sprint TV, VCast) and for DVB-H. But that is not the question. The question is, does VLC support this rate or not? The minimum I see it producing is about 80kbps. Is this a built-in limit to VLC? What other limits are there to its encoding since I have not seen this documented?

[Jerome2]

I've got the same problem... can't get audio bitrates lower than 128 kbps...

[abuze]

try samplerate=48000 instead of ab=48 and see if that is doing what you think of.

[DJ]

try samplerate=48000 instead of ab=48 and see if that is doing what you think of.

Sample Rate is a new command for VLC 0.8.5 and governs the Sampling Frequency NOT the Bit Rate. Although lower Sampling Frequencies do generally produce smaller files at lower Bit Rates. I believe the lowest command supported is samplerate=22050 The standard ranges are: 22050, 44100 and 48000

[abuze]

Ahh but thats strange.. I use it in 0.8.4.a and I have 16000 as value and that works... hmmm

[DJ]

Ahh but thats strange.. I use it in 0.8.4.a and I have 16000 as value and that works... hmmm

Many times things are supported in the core and shut off as they don't work properly. In 0.8.4 the command was not supported and therefore not recognized (ignored).

[abuze]

Ahh then I know. Thanks.