[MEncoder-users] howto find encoding rate of existing flv?

[A. Schmid]

toben blalock wrote:
> Hello,
> 
> I am accepting incoming flv files and re-encoding them if the bit-rate is 
> greater than 500kbps.
> 
> How would I check the bit-rate of an flv file through the command line?

Hmm, that seems to be a problem - that information is obviously not 
present in the header ("mplayer -identify" as well as normal mplayer 
output always shows a bitrate of 0). Perhaps flv is always VBR?

Of course you can calculate the approximate bitrate from file size and 
playing time. For example with a small shell script:

===========================
#!/bin/sh 
 

 
 

output=`mplayer -ao null -vo null -endpos 0 -identify "$1"` 
 

 
 

seconds=`echo "$output" | grep ID_LENGTH | cut -d "=" -f 2` 
 

abitrate=`echo "$output" | grep -m1 ID_AUDIO_BITRATE | cut -d "=" -f 2` 
 

filesize=`stat -c "%s" "$1"` 
 

 
 

echo "scale=2; (8 * $filesize / $seconds - $abitrate) / 1000 " | bc 
 

=========================== 
 


This extracts length and audio bitrate from the header, looks up 
filesize, then calculates the overall bitrate and subtracts the audio 
bitrate.
This means that container overhead as well as other data streams (e.g. 
subtitles, alternative audio streams) and garbage beyond the end of the 
stream will also be counted into video bitrate.

It would be better and a little easier to dump the raw video stream into 
an extra file, but this means extra processing overhead - I don't know 
if that would be acceptable.

Regards
Alex