[Libav-user] How to set bit_rate for MPEG4/2

[Harald Schlangmann]

Thanks for the reply! 

I tested it against a ffmpeg command doing approximately the same (except manipulating the individual frames, slightly different duration):

	ffmpeg -ss 00:06:48.27 -i IN.mp4 -c:v mpeg4 -c:a copy -t 00:01:11.89 -b:v 7257k OUT.mp4

This outputs 

    Stream #0:0(eng): Video: mpeg4 ( [0][0][0] / 0x0020), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 7257 kb/s, 12800 tbn, 25 tbc (default)

and generates a file of size 67.1 MB (roughly matches the expected size - 7722 kb/s).

>  At least constant quantizer vs. bitrate can (and must) be set.


bitrate is clear, constant quantizer matches which field and should be set to which value?

Greetings Harald

-
Harald Schlangmann
Antwerpener Str. 52, 50672 Köln, Germany
+49 151 2265 4439
Harry at gps-laptimer.de
www.gps-laptimer.de

On 20.04.2014, at 17:25, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:

> Harald Schlangmann <harry at ...> writes:
> 
>> Looks I’m doing something fundamentally wrong here.
> 
> Did you test with ffmpeg (the application)?
> I am not convinced that single pass encoding can 
> generally guarantee a target bitrate.
> 
>> Any hint on how to influence result file size for mpeg4?
> 
>> The only other fields I initialize for AVCodecContext 
>> are width, height, time_base, pix_fmt,  
> 
> At least constant quantiser vs. bitrate can (and must) 
> be set.
> 
> Carl Eugen
> 
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> Libav-user mailing list
> Libav-user at ffmpeg.org
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