quality of video edited is poor any suggestions

tkmsr · 11-11-2010, 01:15 AM

I edited some videos via ffmpeg
as follows (it is a Ubuntu 10.04 64 bit server on an SSH connection)

Code:

 ffmpeg -i stats_estimation.mp4 -ar 22050 -acodec libmp3lame -ab 32K -r 25  -vcodec flv out2.flv

Things started perfectly

Code:

FFmpeg version SVN-r0.5.1-4:0.5.1-1ubuntu1, Copyright (c) 2000-2009
Fabrice Bellard, et al.
  configuration: --extra-version=4:0.5.1-1ubuntu1 --prefix=/usr
--enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib
--enable-libgsm --enable-libschroedinger --enable-libspeex
--enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib
--disable-stripping --disable-vhook --enable-runtime-cpudetect
--enable-gpl --enable-postproc --enable-swscale --enable-x11grab
--enable-libdc1394 --enable-shared --disable-static
  libavutil     49.15. 0 / 49.15. 0
  libavcodec    52.20. 1 / 52.20. 1
  libavformat   52.31. 0 / 52.31. 0
  libavdevice   52. 1. 0 / 52. 1. 0
  libavfilter    0. 4. 0 /  0. 4. 0
  libswscale     0. 7. 1 /  0. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Mar  4 2010 12:41:55, gcc: 4.4.3

Seems stream 0 codec frame rate differs from container frame rate:
29.94 (5000/167) -> 44.92 (539/12)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'stats_estimation.mp4':
  Duration: 02:47:05.56, start: 0.000000, bitrate: 237 kb/s
    Stream #0.0(eng): Video: h264, yuv420p, 320x240, 44.92 tbr, 14.97
tbn, 29.94 tbc
    Stream #0.1(eng): Audio: aac, 32000 Hz, stereo, s16
Output #0, flv, to 'out2.flv':
    Stream #0.0(eng): Video: flv, yuv420p, 320x240, q=2-31, 200 kb/s,
90k tbn, 25 tbc
    Stream #0.1(eng): Audio: libmp3lame, 22050 Hz, stereo, s16, 32 kb/s
Stream mapping:
  Stream #0.0 -> #0.0

but the quality of resulting video is very poor.
What I see is when I enlarge the video there are square marks and
objects in video are blurred.

I had tried using

Code:

  ffmpeg -i stats_estimation.mp4 -ar 22050 -acodec libmp3lame -ab 32K -r 25  -s 470x290  -vcodec flv out2.flv

thinking as if size might have been the problem but that did not fixed
the issue I get the out put video as poor where as the video (which is
mp4)
is of good quality and no deterioration in its quality when I see the
unconverted video.
ffmpeg is doing some thing which makes the original quality go.
So any suggestions on this part?

H_TeXMeX_H · 11-11-2010, 11:53 AM

Use '-b' to set the video bitrate, otherwise it defaults to 200k (crap).

tkmsr · 11-11-2010, 09:51 PM

Can you give me idea of what bitrate should I choose I am not clear on this part how do you decide bitrate?

TobiSGD · 11-11-2010, 10:54 PM

It is somewhat simple: Higher bitrate means better quality, but also larger files. Just give it a try and have a look at the results. If the default (200k) is crap, then try it with 400k and look if it is better. If not raise the bitrate again. Be aware that there is no standard solution in picking the bitrate. You can get good looking videos with a lower bitrate if you encode "The Simpsons", but this doesn't have to work with an action film with explosions and stuff.

tkmsr · 11-12-2010, 12:14 AM

H_TeXMeX_H · 11-12-2010, 08:35 AM

Yeah, just pick some bitrates and see what works. If you want the same quality as the input (probably will not work properly in this case) you can use '-sameq'. For variable bit rate (if it is supported by container) use '-qscale <q> =fixed quantizer q = 1 (best) 31 (worst)'.