Statistics
| Branch: | Revision:

ffmpeg / doc / faq.texi @ 87759af9

History | View | Annotate | Download (6.61 KB)

1
\input texinfo @c -*- texinfo -*-
2

    
3
@settitle FFmpeg FAQ
4
@titlepage
5
@sp 7
6
@center @titlefont{FFmpeg FAQ}
7
@sp 3
8
@end titlepage
9

    
10

    
11
@chapter General Problems
12

    
13
@section ffserver does not work. 
14

    
15
ffmpeg development is now concentrated on the codec and format
16
handling. New developments broke ffserver, so don't expect it to work
17
correctly. If you have time and experience, please help us fix it.
18

    
19
@section I cannot read this file although this format seems to be supported by ffmpeg.
20

    
21
Even if ffmpeg can read the file format, it may not support all its
22
codecs. Please consult the supported codec list in the ffmpeg
23
documentation.
24

    
25
@section I get audio/video synchronization problems when grabbing.
26

    
27
Currently, the grabbing stuff does not handle synchronisation
28
correctly. You are free to correct it. A fix is planned.
29

    
30
@section How do I encode JPEGs to another format ?
31

    
32
If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:
33

    
34
@example
35
  ffmpeg -i img%d.jpg /tmp/a.mpg
36
@end example
37

    
38
@samp{%d} is replaced by the image number.
39

    
40
@file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...
41

    
42
The same system is used for the other image formats.
43

    
44
@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
45

    
46
No. FFmpeg only supports open source codecs. Windows DLLs are not
47
portable, bloated and often slow.
48

    
49
@section Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
50

    
51
For multithreaded MPEG* encoding, the encoded slices must be independent,
52
otherwise thread n would practically have to wait for n-1 to finish, so it's
53
quite logical that there is a small reduction of quality. This is not a bug.
54

    
55
@section How can I read from the standard input or write to the standard output ?
56

    
57
Use @file{-} as filename.
58

    
59
@section Why does ffmpeg not decode audio in VOB files ?
60

    
61
The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
62
as the component that handles AC3 decoding (liba52) is currently released under 
63
the GPL. If you have liba52 installed on your system, enable AC3 decoding
64
with @code{./configure --enable-a52}. Take care: by
65
enabling AC3, you automatically change the license of libavcodec from
66
LGPL to GPL.
67

    
68
@section Which codecs are supported by Windows ?
69

    
70
Windows does not support standard formats like MPEG very well, unless you 
71
install some additional codecs
72

    
73
The following list of video codecs should work on most Windows systems
74
@table @option
75
@item msmpeg4v2
76
.avi/.asf
77
@item msmpeg4
78
.asf only
79
@item wmv1
80
.asf only
81
@item wmv2
82
.asf only
83
@item mpeg4
84
only if you have some MPEG-4 codec installed like ffdshow or xvid
85
@item mpeg1
86
.mpg only
87
@end table
88
Note, ASF files often have .wmv or .wma extensions in Windows. It should also 
89
be mentioned that Microsoft claims a patent on the ASF format, and may sue 
90
or threaten users who create ASF files with non-Microsoft software. It is
91
strongly advised to avoid ASF where possible.
92

    
93
The following list of audio codecs should work on most Windows systems
94
@table @option
95
@item adpcm_ima_wav
96
@item adpcm_ms
97
@item pcm
98
@item mp3
99
if some mp3 codec like LAME is installed
100
@end table
101

    
102
@section Why does the chrominance data seem to be sampled at a different time than the luminance data on bt8x8 captures on Linux?
103

    
104
This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at 
105
(@url{http://www.mplayerhq.hu/~michael/bttv-420-2.4.26.patch}). This may also
106
apply cleanly to other 2.4-series kernels.
107

    
108
@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
109

    
110
Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
111
will cause somewhat too strong filtering. A fix is to apply (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
112
or (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
113
and pass 'combfilter=2'.
114

    
115
@section I have a problem with an old version of ffmpeg; where should i report it?
116
Nowhere. Upgrade to the latest release or if there is no recent release upgrade
117
to CVS. You could also try to report it. Maybe you will get lucky and
118
become the first person in history to get an answer different from "upgrade
119
to CVS".
120

    
121
@section -f jpeg doesnt work.
122

    
123
Try '-f image -img jpeg test%d.jpg'.
124

    
125
@section Why can I not change the framerate?
126

    
127
Some codecs, like MPEG-1/2 only allow a small number of fixed framerates.
128
Choose a different codec with the -vcodec command line option.
129

    
130
@section ffmpeg does not work; What is wrong?
131

    
132
Try a 'make distclean' in the ffmpeg source directory. If this does not help see
133
(@url{ffmpeg-bugreport.html}).
134

    
135
@section How do I encode XviD or DivX video with ffmpeg?
136

    
137
Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
138
standard (note that there are many other coding formats that use this
139
same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
140
default fourcc stored in an MPEG-4-coded file will be 'DIVX'. If you want
141
a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will 
142
force the fourcc 'xvid' to be stored as the video fourcc rather than the 
143
default.
144

    
145
@chapter Development
146

    
147
@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
148

    
149
Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
150
examine the source code for one of the many open source projects that 
151
already incorporate ffmpeg at (@url{projects.php}).
152

    
153
@section Can you support my C compiler XXX ?
154

    
155
No. Only GCC is supported. GCC is ported to most systems available and there
156
is no need to pollute the source code with @code{#ifdef}s
157
related to the compiler.
158

    
159
@section Can I use FFmpeg or libavcodec under Windows ?
160

    
161
Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
162
can link the resulting DLLs with any other Windows program. Read the
163
@emph{Native Windows Compilation} section in the FFmpeg documentation
164
to find more information.
165

    
166
@section Can you add automake, libtool or autoconf support ?
167

    
168
No. These tools are too bloated and they complicate the build. Moreover,
169
since only @samp{gcc} is supported they would add little advantages in
170
terms of portability.
171

    
172
@section Why not rewrite ffmpeg in object-oriented C++ ?
173

    
174
ffmpeg is already organized in a highly modular manner and does not need to
175
be rewritten in a formal object language. Further, many of the developers 
176
favor straight C; it works for them. For more arguments on this matter,
177
read "Programming Religion" at (@url{http://lkml.org/faq/lkmlfaq-15.html}).
178

    
179
@section Why are the ffmpeg programs devoid of debugging symbols ?
180

    
181
The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
182
information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
183
you need the debug information, used the *_g versions.
184

    
185
@bye