[MPlayer-users] Bug report - mencoder incorrectly handles some FLV files

[Liran Zvibel]

On 3 Sep 2012, at 18:58, Carl Eugen Hoyos wrote:
>> I'm currently using ffmpeg to decode the frames from flv 
>> files and reencode them later on. I've tried switching to 
>> mencoder, as it processes the files much faster.
> 
> This makes absolutely no sense (MEncoder is using FFmpeg 
> to decode files and it is mostly using the same encoders 
> as FFmpeg).

> Please elaborate, Carl Eugen

FLV files are encoded using variable frame-rate. FFMPEG usually recognizes it as frame-rate of 1000, 
so when just using ffmpeg to decode the frames it runs for ages and you get huge files with over-resampling of the data.

What I'm doing with ffmpeg then is :
	ffmpeg -i <FLV_FILE> -an -r 25 -f rawvideo -vcodec rawvideo -pix_fmt yuv420p -
The comparable mencoder command line is:
	mencoder <FLV_FILE> -nosound -ovc raw -of rawvideo -really-quiet  -mc 0 -noskip -o -

The ffmpeg command forces resampling of frames, and the mencoder command simply decodes the FLV Sorenson Park codec.
The mencoder command runs significantly faster than the ffmpeg command. I pick '-r 25' for the ffmpeg line as many videos approach that quality (though some have average of 15 or even 6 frames per second)

I get the number of frames in the mencoder by dividing the size of the output by the size of a single frame, and thus deduct average frame rate to use later (since I know the duration).
My method with mencoder produces adequate results and for large number of files finishes significantly faster.

Hopefully now you better understand my situation.

Thanks,
Liran Zvibel.