* adding Michael's explanation to the FAQ
[libav.git] / doc / faq.texi
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 doesn't 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 suppored 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 synchro problems when grabbing.
26
27 Currently, the grabbing stuff does not handle synchronisation
28 correctly. You are free to correct it. It is planned to fix it ASAP.
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 its
53 quite logic 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 Audio is not decoded in VOB files ?
60
61 AC3 decoding is optional as the codec is currently released under the
62 GPL. Enable it with @code{./configure --enable-a52}. Take care: by
63 enabling AC3, you automatically change the license of libavcodec from
64 LGPL to GPL.
65
66 @section Which codecs are supported by windows ?
67
68 Windows does not support standard formats like mpeg very well, unless you
69 install some additional codecs
70
71 The following list of video codecs should work on most windows systems
72 @table @option
73 @item msmpeg4v2
74 .avi/.asf
75 @item msmpeg4
76 .asf only
77 @item wmv1
78 .asf only
79 @item wmv2
80 .asf only
81 @item mpeg4
82 only if you have some mpeg4 codec installed like ffdshow or xvid
83 @item mpeg1
84 .mpg only
85 @end table
86 note, asf often uses .wmv or .wma extensions in windows, it should also be
87 mentioned that asf is patented, so microsoft may sue or threaten users who
88 use it if they see any reason to do so, it is strongly recommanded to avoid asf
89 for any use
90
91 The following list of audio codecs should work on most windows systems
92 @table @option
93 @item adpcm_ima_wav
94 @item adpcm_ms
95 @item pcm
96 @item mp3
97 if some mp3 codec like lame is installed
98 @end table
99
100 @section The chrominance seems to come from a different time then the luminance on bt8x8 captures on linux?
101
102 well known bug in the bt8x8 driver, for 2.4.26 theres a patch at
103 (@url{http://www.mplayerhq.hu/~michael/bttv-420-2.4.26.patch}), i suspect that
104 this will also apply cleanly to other 2.4 kernels
105
106 @section How to avoid the ugly aliassing artefacts in bt8x8 captures on linux?
107
108 pass 'combfilter=1 lumafilter=1' to the bttv driver, note though that 'combfilter=1'
109 will cause somewhat too strong filtering, a fix is too apply (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
110 or (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
111 and pass 'combfilter=2'
112
113 @section I have a problem with an old version of ffmpeg, where should i report it?
114 Nowhere, upgrade to the latest release or if there is no recent release upgrade
115 to cvs, you could also try to report it, maybe you are lucky and
116 will become the first person in history to get a different awnser from "upgrade
117 to cvs".
118
119 @section -f jpeg doesnt work.
120
121 try '-f image -img jpeg test%d.jpg'
122
123 @chapter Development
124
125 @section Are there examples of use of the FFmpeg libraries libavcodec and libavformat ?
126
127 Yes. Read the Developers Guide of the FFmpeg documentation.
128
129 @section Can you support my C compiler XXX ?
130
131 No. Only GCC is supported. GCC is ported on most systems available and I
132 don't see the need to pollute the source code with @code{#ifdef}s
133 related to the compiler.
134
135 @section Can I use FFmpeg or libavcodec under Windows ?
136
137 Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
138 can link the resulting DLLs with any other Windows program. Read the
139 @emph{Native Windows Compilation} section in the FFmpeg documentation
140 to have more information.
141
142 @section Can you add automake, libtool or autoconf support ?
143
144 No. These tools are too blowted and they complicate the build. Moreover,
145 since only @samp{gcc} is supported they would add little advantages in
146 terms of portability.
147
148 @section ffmpeg doesnt contain any debugging symbols ?
149
150 try ffmpeg_g, ffplay_g, ...
151
152 @bye