[Ffmpeg-devel] closed captioning bug?
Sat Apr 22 08:10:17 CEST 2006
Michael Niedermayer wrote:
> On Fri, Apr 21, 2006 at 01:26:09PM -0400, Cyrus A wrote:
>> Closed captioning bug report:
>> kernel - 2.6.15-1.2054_FC5
>> processor - AMD 64 X2 3800
>> ffmpeg version - cvs from April 21, 2006
>> bttv: Winfast 2000 Deluxe (seems to be in perfect working order)
>> It seems there is a but with closed captioning when using ffmpeg on
>> x86_64 architecture. The captioning I recorded (using ntsc-cc and
>> zvbi-ntsc-cc) is garbled... it's just as if every other letter or
>> sometimes groups of letters are removed. Here is an example where I
>> started ntsc-cc with tvtime, then turned on ffmpeg:
>> HUNDREDS OF DEMONSTRATORS CAME
>> OUT TO DENOUNCE CHINA'S
>> COMMUNIST GOVERNMENT AND THE BAN
>> OF FALUN GONG UNIT.
>>> WELL THE WOMA W SCREENED <------------ ffmpeg turned on
>> AT PSIDENT HU THE WTE
>> HOEYESTERY DUEN COT
>> IS AERNO BUT T CORC AN
>> RLIER CNN POR, SHE H NOT
>> BE CHAED WITH TEANG
>> FOREIGN OFFICIAL
>> IS WASNFORTIE GOT FROM
>> E HER ATTNEY.
>> The funny thing is, I tried several combinations of programs that use
>> /dev/vbi0 in some way and *sometimes* the caps work well. Ffmpeg seems
>> to be the weak link that "breaks" the captions. Here is my evidence:
>> zvbi-ntsc-cc by itself: CAPTIONS OK
>> tvtime with ntsc-cc : CAPTIONS OK
>> tvtime with zvbi-ntsc-cc: CAPTIONS OK
>> tvtime with ffmpeg with ntsc-cc: CAPTIONS OK
>> ffmpeg with zvbi-ntsc-cc: CAPTIONS GARBLED
>> ffmpeg with ntsc-cc: CAPTIONS VERY GARBLED
>> NOTE: zvbi seems to perform better than ntsc-cc when each is run alone
>> with ffmpeg
>> Here is my ffmpeg command:
>> [cyrus at localhost ~]$ /home/cyrus/ffmpeg/ffmpeg -ad /dev/audio -vd
>> /dev/video0 -s 320x256 -y -r ntsc /home/cyrus/test.mpg
>> FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
>> configuration: --enable-mp3lame --cpu=x86_64
>> libavutil version: 49.0.0
>> libavcodec version: 51.9.0
>> libavformat version: 50.4.0
>> built on Apr 21 2006 12:28:44, gcc: 4.1.0 20060304 (Red Hat 4.1.0-3)
>> Input #0, video4linux, from '':
>> Duration: N/A, bitrate: N/A
>> Stream #0.0, 29.97 fps(r): Video: rawvideo, yuv420p, 320x256, 29461 kb/s
>> Input #1, audio_device, from '':
>> Duration: N/A, bitrate: N/A
>> Stream #1.0: Audio: pcm_s16le, 44100 Hz, mono, 705 kb/s
>> Output #0, mpeg, to '/home/cyrus/test.mpg':
>> Stream #0.0, 29.97 fps(c): Video: mpeg1video, yuv420p, 320x256,
>> q=2-31, 200 kb/s
>> Stream #0.1: Audio: mp2, 44100 Hz, mono, 64 kb/s
>> Stream mapping:
>> Stream #0.0 -> #0.0
>> Stream #1.0 -> #0.1
>> Press [q] to stop encoding
>> [mpeg1video @ 0x8d0590]warning, clipping 1 dct coefficients to -255..255
>> frame= 1488 q=12.7 Lsize= 1894kB time=49.5 bitrate= 313.4kbits/s
>> video:304kB audio:387kB global headers:0kB muxing overhead 174.221079%
>> NOTE: It doesn't seem to matter which encoding scheme I'm using. mpeg1,
>> mpeg4, mp2, mp3... they all show the same behavior.
>> Any help would be greatly appreciated.
> ok, ive not the faintest idea whats wrong but does chaning the
> resolution / encoding to /dev/null using -vcodec copy help?
> btw, are there any distortions in the video vissible?
> maybe the diskaccess for encoding is causing some buffers of the
> capture hw to overrun in that case hdparm / pci settings
> might have some effect
The video recorded with ffmpeg, when played back, is slightly choppy.
Not strobe, freeze-frame choppy, but you can tell something isn't right.
It's as if it's an MTV "Cribs" effect or something. The portions of
video where tvtime is also running in the background are smoother than
those recorded with only ffmpeg running. Does this help? What can I try now?
Changing the resolution didn't help. I was unable to use /dev/null. I'm
not an ffmpeg expert so I don't know exactly what I'm doing. I just
replaced the filename with /dev/null but got an error message saying
/dev/null unavailable or something. I also tried it with -vcodec copy
and got the same error.
Also, FYI, I tested another brand and model bttv card and got the exact
Let me know what I should try next.
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