Hey guys,
I'm transcoding with ffmpeg API . but the video frame rate of the target
file is far from accuracy .
such as I wanna to get a target file with h263 encode type and 22kbps video
frame rate, but I get a result file with video bitrate 26kbps, h263 encode
type , which is far from accuracy .
I test it using ffmpeg.exe official release with the same source file and
the same paremeter for target file, but get the same result.
why I cann't get the set video bitrate under CBR mode? Is there any body know
this ?
here are concrete information:
my source file parameter is :
video: encode type : wmv3 resolution ratio: 176*144 bitrate: 2000kbps
framte rate:25fps
audio: encode type: wmav2 bitrate: 128kbps sample rate: 48k Hz
channels: 2
my target file parameter is :
video: encode type: h263 resolution ratio: 176*144, bitrate: 22kbps,
frame rate: 5fps
audio: encode type:amr-nb bitrate 6kbps, Mono, sample rate 8kHz
channels: 1
I use ffmpeg.exe to transcode as follows:
ffmpeg.exe -i cq-SD.wmv -vcodec h263 -r 5 -b:v 22k -ar 8000 -s 176*144 -acodec
libopencore_amrnb -ac 1 -b:a 8k 44.3gp
and also I use ffmpeg API to transcode with the encode parameter set as follows:
AVCodecContext * c = st->codec;
br = 22000;
c->codec_id = codec_id;
c->width = 176;
c->height = 144;
c->bit_rate = 22000;
c->rc_min_rate = br;
c->rc_max_rate = br;
c->time_base.den = 5;
c->time_base.num = 1;
but the result file I get is like this:
video: encode type: h263 resolution ratio: 176*144, bitrate: 26kbps,
frame rate: 5fps
audio: encode type:amr-nb bitrate 6kbps, Mono, sample rate 8kHz
channels: 1
Any advice will be appreciated!
Thanks!
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