faq


Languages : news about manual install configuration usage advanced usage options FAQ download contact / bugs links	FAQ 1) Why no mp3 ? Tuxrip does not encode audio in mp3 format and will probably never support it (despite its GPL licence authorises any 3rd party patch). Two reasons : - a technical one : vorbis format is far better than mp3. Try it and you'll never change back. The sound has a better dynamic. Moreover, the compression rate is higher and thus more bits are reserved for the video stream, which will have a better quality. - legal and ethical : vorbis is a Free format (like Free-speech) published under a BSD-like licence. It is fully documented and not endorsed by any patent. This format will be Free forever. On the other hand, the mp3 is patented and is a proprietary format belonging by Thomson and Fraunhoeffer. Reading and encoding mp3 is for the moment free for individual use, but they may claim fees at any time. To conclude : why using a proprietary format when there is a free and better equivalent one ? 2a) OK but how do I play these .ogm files under Windows ? No problem here, just install the ogg direct show filter available here : http://tobias.everwicked.com/oggds.htm (a mirror is available on http://www.doom9.org). You may play any mpeg4 file with WMP or any other multimedia player (recommended ;)) 2b) Isn't it a pain in the *** to have to install a new codec ? Why ? It was not a pain to install a mpeg4 codec like DivX or XviD ? Note that vorbis is is natively supported in Winamp, this is not unknown under Windows. 2c) And libavcodec under Windows ? There is no particular codec to install ? libavcodec is an mpeg4 codec, not a format, like DivX or XviD. It can be read by any media player capable of reading mpeg4 video files. Any other mpeg4 codec is in general ok. You may also install the excellent playing and post-processing filters like ffdshow (http://cutka.szm.sk/ffdshow/). ffdshow is able to read any mpeg4 file (div3/4/5, xvid, libavcodec...). 3) What about XviD ? By default, tuxrip encodes the video using the libavc codec, but can also use XviD using the option --xvid. XviD and libavcodec are both mpeg4 codecs. The only difference is in the encoding algorithm, and the result image can have different look. Some people prefer libavcodec, some prefer XviD, and moreover, these two codecs are constantly updated. Try them ! And you'll get your own idea. Moreover, both codecs have a lot of different parameters (quantizers settings, dark and lumi masking,...) It seems that libavc gives a (very) little more detailed image. On the other hand, XviD has an excellent processing at high bitrate and shows less "blocks". Note that some post-processing filters can attenuate the block aspects too (you need to find a compromise beetween blur and blocks). 4) What about the DivX 5 ? The problem is the same than for the mp3 format : it is proprietary and contains a spyware (Gator). Moreover the two Free codecs libavcodec and XviD show a lot better quality. 5) I have movies in Divx3;), DivX4, DivX5, XviD, libavcodec. Do I need a different codec for each one ? No. Don't confuse codec and format. All these different codecs encode video with different algorithms, but use the same format : mpeg4. If all these project offer their own decoder, only one of them is necessary, since they need to decode only one format, the mpeg4. The best one is the only one you need : libavcodec/ffmpeg. MPlayer uses libavcodec to decode mpeg4 under Unix. Under Windows, you just need the ffdshow filters (see FAQ 2c). 6) What is the quality factor QF ? What are the recommended values ? The QF corresponds to the number of bits by pixel and by frame. As a rule of thumb, the higher it is, the better the image is. However, the size of the movie is limited by the size of the support (in general, 1 or 2 CD), thus the number of bits is limited, and a compromise has to be found between compression and quality. The QF depends on the bitrate and the image resolution. In general, to increase the QF, the movie resolution is decreased, since the bitrate depends on the support size and the movie length, which are fixed values. Below 0.18, you obtain often a low quality image, since there are not enough pixels to encode with enough detail : you get a lot of squares, a very "blocky" image. As a rule of thumb, recommended values are 0.20-0.22 for 1CD and 0.26-0.28 for 2 CDs. The QF value is variable : it is sometimes possible to go as low as 0.18 for Bergman, but not for Matrix. However, going above 0.30 is an overkill. The --check-comp option is used to make a compressibility check on a sample of the movie, taken at different positions. Thus it helps choosing the optimal QF for that particular movie. 7) What is the aspect ratio ? Is that possible to calculate with the DVD image resolution in pixels the format of the compressed movie, in pixels ? Not directly. This is because of the mpeg2 format used by the DVD : a movie can be encoded in 720x576 pixels, but displayed as a 1024x576 pixels image. It is called anamorphosis : actually the image is encoded as deformed, compressed, and has to be set right by the player. The header of a mpeg2 file contains the factor the player has to use to display the redressed image, and it is called "aspect ratio". For instance, a DVD PAL is always encoded in 720x576, thus the height and the width have a 1.25 ratio. However, the movie can have an aspect ratio of 4/3 (1.33) or 16/9 (1.78). Thus the player has to increase the length of the image by a 1.33/1.25 ratio or a 1.78/1.25 ratio, respectively. Larger ratios, like 2.35 (cinemascope) or 2.21 are obtained by adding black borders on top and bottom of a 16/9 encoded image. On the other hand, an mpeg4 video file (avi or ogm) is not anamorphosed (Note that MPlayer can support this option, but it seems to be the only one to do it !) Its pixel resolution corresponds to the displayed resolution. Then encoding a DVD in mpeg4 format leads to removing the black borders (cropping), but also calculating final resolution considering the aspect ratio. 8) What is the quality factor of the vorbis sound format ? When encoding sound with vorbis, it is better to give a quality factor instead of a bitrate to the encoder parameters. Here is the approximate relationship between bitrate and vorbis quality : `0.00 -> 64kbps 0.50 -> 72kbps 1.00 -> 80 kbps 2.00 -> 96 kbps 3.00 -> 112 kbps 4.00 -> 128 kbps 5.00 -> 160 kbps 7.00 -> 224 kbps 10.00 -> 500 kbps` Note : don't forget that vorbis has a better quality than mp3 at equal bitrate. Encoding a movie with factor 1 is in general enough, since 80kbps vorbis is at least as good as 128kbps mp3. 9) What is deinterlacing ? Interlacing is a technique developped for TV, to reduce the effect of scintillation of the screen when showing a movie at 25 i/s (PAL) or 30 i/s (NTSC). The movie is brodcast at twice this frequency, as half images containing the odd lines and then the even lines. The persisting effect of the screen makes this unnoticeable for the human eye and reduces scintillation. Most of DVD region 2 are encoded as PAL non interlaced. They do not need any image processing to be encoded. However, some titles in PAL may be interlaced (in general the bonuses) and all NTSC DVD (regions 1 and 4). When motion is high (e.g. when camera is doing a travelling), some interlacing artifacts appear (like image hashing). A deinterlacing filter is then necessary. Tuxrip is able to automatically detect if the DVD is NTSC and then uses a deinterlacing filter. However, in case of an interlaced PAL movie, tuxrip needs to be run with the --deintrelace option (see options, part 3). More information about interlacing can be found on http://nickyguides.digital-digest.com/interlace.htm. 10) And the subtitles ? Their support will be integrated in tuxrip soon. 11) I could encode last week in libavcodec and xvid. Since I use a new CVS version of MPLayer, it does not work anymore !Encoding stops with the error message : Exiting... (error parsing cmdline) It may happen that the codec options change, and their syntax become different, which makes MPlayer crash. In that case, edit the .tuxriprc file and correct the syntax. For instance : from mplayer-0.90pre10 to the CVS 7/12/2002, xvid options : min_quantizer and max_quantizer have been replaced with quant_range. You may find the changes in "man mplayer" (especially in --lavcopts and --xvidencopts sections). 12) Are there known bugs ? Yes, and not essentially in tuxrip ! There are troubles with some particular DVD title : a "bonus" (the trailer) in the UK edition of "Entrapment". The audio layer number was not corresponding with the displayed one. In that case, enter a different number (1 instead of 0). Such errors are rare though, but it is good to be aware :)

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FAQ

1) Why no mp3 ?

Tuxrip does not encode audio in mp3 format and will probably never support it (despite its GPL licence authorises any 3rd party patch). Two reasons :
- a technical one : vorbis format is far better than mp3. Try it and you'll never change back. The sound has a better dynamic. Moreover, the compression rate is higher and thus more bits are reserved for the video stream, which will have a better quality.
- legal and ethical : vorbis is a Free format (like Free-speech) published under a BSD-like licence. It is fully documented and not endorsed by any patent. This format will be Free forever. On the other hand, the mp3 is patented and is a proprietary format belonging by Thomson and Fraunhoeffer. Reading and encoding mp3 is for the moment free for individual use, but they may claim fees at any time.
To conclude : why using a proprietary format when there is a free and better equivalent one ?

2a) OK but how do I play these .ogm files under Windows ?

No problem here, just install the ogg direct show filter available here : http://tobias.everwicked.com/oggds.htm (a mirror is available on http://www.doom9.org). You may play any mpeg4 file with WMP or any other multimedia player (recommended ;))

2b) Isn't it a pain in the *** to have to install a new codec ?

Why ? It was not a pain to install a mpeg4 codec like DivX or XviD ? Note that vorbis is is natively supported in Winamp, this is not unknown under Windows.

2c) And libavcodec under Windows ? There is no particular codec to install ?

libavcodec is an mpeg4 codec, not a format, like DivX or XviD. It can be read by any media player capable of reading mpeg4 video files. Any other mpeg4 codec is in general ok. You may also install the excellent playing and post-processing filters like ffdshow (http://cutka.szm.sk/ffdshow/). ffdshow is able to read any mpeg4 file (div3/4/5, xvid, libavcodec...).

3) What about XviD ?

By default, tuxrip encodes the video using the libavc codec, but can also use XviD using the option --xvid. XviD and libavcodec are both mpeg4 codecs. The only difference is in the encoding algorithm, and the result image can have different look. Some people prefer libavcodec, some prefer XviD, and moreover, these two codecs are constantly updated. Try them ! And you'll get your own idea. Moreover, both codecs have a lot of different parameters (quantizers settings, dark and lumi masking,...)
It seems that libavc gives a (very) little more detailed image. On the other hand, XviD has an excellent processing at high bitrate and shows less "blocks". Note that some post-processing filters can attenuate the block aspects too (you need to find a compromise beetween blur and blocks).

4) What about the DivX 5 ?

The problem is the same than for the mp3 format : it is proprietary and contains a spyware (Gator). Moreover the two Free codecs libavcodec and XviD show a lot better quality.

5) I have movies in Divx3;), DivX4, DivX5, XviD, libavcodec. Do I need a different codec for each one ?

No. Don't confuse codec and format. All these different codecs encode video with different algorithms, but use the same format : mpeg4. If all these project offer their own decoder, only one of them is necessary, since they need to decode only one format, the mpeg4. The best one is the only one you need : libavcodec/ffmpeg. MPlayer uses libavcodec to decode mpeg4 under Unix. Under Windows, you just need the ffdshow filters (see FAQ 2c).

6) What is the quality factor QF ? What are the recommended values ?

The QF corresponds to the number of bits by pixel and by frame. As a rule of thumb, the higher it is, the better the image is. However, the size of the movie is limited by the size of the support (in general, 1 or 2 CD), thus the number of bits is limited, and a compromise has to be found between compression and quality. The QF depends on the bitrate and the image resolution. In general, to increase the QF, the movie resolution is decreased, since the bitrate depends on the support size and the movie length, which are fixed values.
Below 0.18, you obtain often a low quality image, since there are not enough pixels to encode with enough detail : you get a lot of squares, a very "blocky" image. As a rule of thumb, recommended values are 0.20-0.22 for 1CD and 0.26-0.28 for 2 CDs.
The QF value is variable : it is sometimes possible to go as low as 0.18 for Bergman, but not for Matrix. However, going above 0.30 is an overkill.

The --check-comp option is used to make a compressibility check on a sample of the movie, taken at different positions. Thus it helps choosing the optimal QF for that particular movie.

7) What is the aspect ratio ? Is that possible to calculate with the DVD image resolution in pixels the format of the compressed movie, in pixels ?

Not directly. This is because of the mpeg2 format used by the DVD : a movie can be encoded in 720x576 pixels, but displayed as a 1024x576 pixels image. It is called anamorphosis : actually the image is encoded as deformed, compressed, and has to be set right by the player. The header of a mpeg2 file contains the factor the player has to use to display the redressed image, and it is called "aspect ratio".
For instance, a DVD PAL is always encoded in 720x576, thus the height and the width have a 1.25 ratio. However, the movie can have an aspect ratio of 4/3 (1.33) or 16/9 (1.78). Thus the player has to increase the length of the image by a 1.33/1.25 ratio or a 1.78/1.25 ratio, respectively. Larger ratios, like 2.35 (cinemascope) or 2.21 are obtained by adding black borders on top and bottom of a 16/9 encoded image.
On the other hand, an mpeg4 video file (avi or ogm) is not anamorphosed (Note that MPlayer can support this option, but it seems to be the only one to do it !) Its pixel resolution corresponds to the displayed resolution. Then encoding a DVD in mpeg4 format leads to removing the black borders (cropping), but also calculating final resolution considering the aspect ratio.

8) What is the quality factor of the vorbis sound format ?

When encoding sound with vorbis, it is better to give a quality factor instead of a bitrate to the encoder parameters. Here is the approximate relationship between bitrate and vorbis quality :

0.00 -> 64kbps 0.50 -> 72kbps 1.00 -> 80 kbps 2.00 -> 96 kbps 3.00 -> 112 kbps 4.00 -> 128 kbps 5.00 -> 160 kbps 7.00 -> 224 kbps 10.00 -> 500 kbps

Note : don't forget that vorbis has a better quality than mp3 at equal bitrate. Encoding a movie with factor 1 is in general enough, since 80kbps vorbis is at least as good as 128kbps mp3.

9) What is deinterlacing ?

Interlacing is a technique developped for TV, to reduce the effect of scintillation of the screen when showing a movie at 25 i/s (PAL) or 30 i/s (NTSC). The movie is brodcast at twice this frequency, as half images containing the odd lines and then the even lines. The persisting effect of the screen makes this unnoticeable for the human eye and reduces scintillation.
Most of DVD region 2 are encoded as PAL non interlaced. They do not need any image processing to be encoded. However, some titles in PAL may be interlaced (in general the bonuses) and all NTSC DVD (regions 1 and 4). When motion is high (e.g. when camera is doing a travelling), some interlacing artifacts appear (like image hashing). A deinterlacing filter is then necessary.
Tuxrip is able to automatically detect if the DVD is NTSC and then uses a deinterlacing filter. However, in case of an interlaced PAL movie, tuxrip needs to be run with the --deintrelace option (see options, part 3).
More information about interlacing can be found on http://nickyguides.digital-digest.com/interlace.htm.

10) And the subtitles ?

Their support will be integrated in tuxrip soon.

11) I could encode last week in libavcodec and xvid. Since I use a new CVS version of MPLayer, it does not work anymore !Encoding stops with the error message : Exiting... (error parsing cmdline)

It may happen that the codec options change, and their syntax become different, which makes MPlayer crash. In that case, edit the .tuxriprc file and correct the syntax.
For instance : from mplayer-0.90pre10 to the CVS 7/12/2002, xvid options : min_quantizer and max_quantizer have been replaced with quant_range. You may find the changes in "man mplayer" (especially in --lavcopts and --xvidencopts sections).

12) Are there known bugs ?
Yes, and not essentially in tuxrip ! There are troubles with some particular DVD title : a "bonus" (the trailer) in the UK edition of "Entrapment". The audio layer number was not corresponding with the displayed one. In that case, enter a different number (1 instead of 0). Such errors are rare though, but it is good to be aware :)