[MPlayer-cvslog] CVS: main/DOCS/tech encoding-guide.txt,1.2,1.3
Guillaume Poirier CVS
syncmail at mplayerhq.hu
Sat Feb 11 23:11:14 CET 2006
CVS change done by Guillaume Poirier CVS
Update of /cvsroot/mplayer/main/DOCS/tech
In directory mail:/var2/tmp/cvs-serv6895
Modified Files:
encoding-guide.txt
Log Message:
Remove all the sections that are now merged in the XML doc
Index: encoding-guide.txt
===================================================================
RCS file: /cvsroot/mplayer/main/DOCS/tech/encoding-guide.txt,v
retrieving revision 1.2
retrieving revision 1.3
diff -u -r1.2 -r1.3
--- encoding-guide.txt 20 Oct 2005 13:45:41 -0000 1.2
+++ encoding-guide.txt 11 Feb 2006 22:11:11 -0000 1.3
@@ -37,303 +37,6 @@
-I. Preparing to encode
-
-Before you even think about encoding a movie, you need to take several
-preliminary steps to
-
-
-I.1. Identifying source material and framerate
-
-The first and most important step before you encode should be
-determining what type of content you're dealing with. If your source
-material comes from DVD or broadcast/cable/satellite TV, it will be
-stored in one of two formats: NTSC for North America and Japan, and
-PAL for Europe, etc. But it's important to realize that this is just
-the formatting for presentation on a television, and often does NOT
-correspond to the original format of the movie. In order to produce a
-suitable encode, you need to know the original format. Failure to take
-this into account will result in ugly combing (interlacing) artifacts
-in your encode, and will greatly reduce the quality/bitrate ratio of
-the encoder!
-
-Here is a list of common types of source material, where you're likely
-to find them, and their properties:
-
-Standard Film: Produced for theatrical display at 24fps.
-
-PAL video: Recorded with a PAL video camera at 50 fields per second. A
-field consists of just the even or odd numbered lines of a frame.
-Television was designed to refresh these in alternation as a cheap
-form of analog compression. The human eye supposedly compensates for
-this, but once you understand interlacing you'll learn to see it on TV
-too and never enjoy TV again. Two fields do NOT make a complete frame,
-because they are captured 1/50 of a second apart in time, and thus
-they do not line up unless there is no motion.
-
-NTSC Video: Recorded with an NTSC video camera at 59.94 fields per
-second, or 60 fields per second in the pre-color era. Otherwise
-similar to PAL.
-
-Animation: Usually drawn at 24fps, but animation also comes in
-mixed-framerate varieties.
-
-Computer Graphics (CG): Can be any framerate, but 24 and 30 fps are
-the most frequently encountered in NTSC regions, and 25 fps in PAL
-regions.
-
-Old Film: Various lower framerates.
-
-Movies consisting of frames are referred to as progressive, while
-those consisting of independent fields are called interlaced, or
-sometimes video, although this latter term is ambiguous.
-
-To further complicate matters, some movies will be a mix of several of
-the above.
-
-The most important distinction to make between all of these formats is
-that some are frame-based, while others are field-based. WHENEVER a
-movie is prepared for display on television (including DVD), it is
-converted to a field-based format. The various methods by which this
-can be done are collectively referred to as "pulldown", of which the
-infamous NTSC "3:2 telecine" is one variety. Unless the original
-material was also field-based (and the same fieldrate), you are
-getting the movie in a format other than the original.
-
-There are several common types of pulldown:
-
-PAL 2:2 pulldown: The nicest of them all. Each frame is shown for two
-fields duration, by extracting the even and odd lines and showing them
-in alternation. If the original material is 24fps, this process speeds
-up the movie by 4%.
-
-PAL 2:2:2:2:2:2:2:2:2:2:2:3 pulldown: Every 12th frame is shown for
-three fields duration, instead of just two. This avoids the 4% speedup
-issue, but makes the process much more difficult to reverse. It is
-usually seen in musical productions where adjusting the speed by 4%
-would seriously damage the musical score.
-
-NTSC 3:2 telecine: Frames are shown alternatively for 3 fields or 2
-fields duration. This gives a fieldrate 5/2 times the original
-framerate. The result is also slowed down very slightly from 60 fields
-per second to 59.94 fields per second to maintain NTSC fieldrate.
-
-NTSC 2:2 pulldown: Used for showing 30fps material on NTSC. Nice, just
-like 2:2 PAL pulldown.
-
-There are also methods for converting between NTSC and PAL video. Such
-topics are beyond the scope of this guide. If you encounter such a
-movie and want to encode it, your best bet is to find a copy in the
-original format. NTSC/PAL conversion is highly destructive and cannot
-be reversed cleanly, so your encode will greatly suffer if it is made
-from a converted source.
-
-When video is stored on DVD, consecutive pairs of fields are grouped
-as a frame, even though they are not intended to be shown at the same
-moment in time. The MPEG2 standard used on DVD and digital TV provides
-a way to encode the original progressive frames, and store the number
-of fields for which each should be shown in the frame headers. If this
-method has been used, the term "soft telecine" will often be used to
-describe the movie, since the process only directs the DVD player to
-apply pulldown to the movie rather than altering the movie itself.
-This case is highly preferable since it can easily be reversed
-(actually ignored) by the encoder, and since it preserves maximal
-quality. However, many DVD and broadcast production studios do not use
-proper encoding techniques, and instead produce movies with "hard
-telecine", where fields are actually duplicated in the encoded MPEG2.
-
-The procedures for dealing with these cases will be covered later in
-this guide. For now, we leave you with some guides to identifying
-which type of material you're dealing with:
-
-NTSC regions:
-
-- If MPlayer prints that the framerate has changed to 23.976 when
- watching your movie, and never changes back, it's almost certainly
- 24fps content that has been "soft telecined".
-
-- If MPlayer shows the framerate switching back and forth between
- 23.976 and 29.97, and you see "combing" at times, then there are
- several possibilities. The 23.976 fps segments are almost certainly
- 24fps progressive content, "soft telecined", but the 29.97 fps parts
- could be either hard-telecined 24fps content or NTSC video content.
- Use the same guidelines as the following two cases to determine
- which.
-
-- If MPlayer never shows the framerate change, and every single frame
- with motion appears combed, your movie is NTSC video at 59.94 fields
- per second.
-
-- If MPlayer never shows the framerate change, and two frames out of
- every five appear combed, your movie is "hard telecined" 24fps
- content.
-
-PAL regions:
-
-- If you never see any combing, your movie is 2:2 pulldown.
-
-- If you see combing alternating in and out every half second, then
- your movie is 2:2:2:2:2:2:2:2:2:2:2:3 pulldown.
-
-- If you always seem combing during motion, then your movie is PAL
- video at 50 fields per second.
-
-Hint: MPlayer can slow down movie playback with the -speed option. Try
-using -speed 0.2 to watch the movie very slowly and identify the
-pattern, if you can't see it at full speed.
-
-
-I.2. Selecting the quality you want
-
-It's possible to encode your movie at a wide range of qualities. With
-modern video encoders and a bit of pre-codec compression (downscaling
-and denoising), it's possible to achieve very good quality at 700 MB,
-for a 90-110 minute widescreen movie. And all but the longest movies
-can be encoded with near-perfect quality at 1400 MB.
-
-If you do not plan to store your movies on CD or other size-limited
-media, and you want maximal quality at all costs, you can encode in
-constant quantizer mode, which will not aim to meet a specific target
-bitrate or filesize but instead use the maximal accuracy encoding for
-all frames. This is not recommended in most cases, because you can
-achieve significantly smaller file sizes without noticeable loss.
-However, it may be desirable for the hardcore archivists out there.
-
-
-I.4. Cropping and scaling
-
-Recall from the previous section that the final picture size you
-encode should be a multiple of 16 (in both width and height). This can
-be achieved by cropping, scaling, or a combination of both.
-
-When cropping, there are a few guidelines that must be followed to
-avoid damaging your movie. The normal YUV format, 4:2:0, stores chroma
-(color) information subsampled, i.e. chroma is only sampled half as
-often in each direction as luma (intensity) information. Observe this
-diagram, where L indicates luma sampling points and C chroma.
-
- L L L L L L L L
- C C C C
- L L L L L L L L
-
- L L L L L L L L
- C C C C
- L L L L L L L L
-
-As you can see, rows and columns of the image naturally come in pairs.
-Thus your crop offsets and dimensions MUST be even numbers. If they
-are not, the chroma will no longer line up correctly with the luma. In
-theory, it's possible to crop with odd offsets, but it requires
-resampling the chroma which is potentially a lossy operation and not
-supported by the crop filter.
-
-Further, interlaced video is sampled as follows:
-
- TOP FIELD BOTTOM FIELD
-
- L L L L L L L L
- C C C C
- L L L L L L L L
-
- L L L L L L L L
- C C C C
- L L L L L L L L
-
- L L L L L L L L
- C C C C
- L L L L L L L L
-
- L L L L L L L L
- C C C C
- L L L L L L L L
-
-As you can see, the pattern does not repeat until after 4 lines. So
-for interlaced video, your y-offset and height for cropping must be
-multiples of 4.
-
-So how do you determine a crop rectangle to begin with? Sometimes you
-can guess, but the cropdetect filter in MPlayer can make it easy. Run
-MPlayer with -vf cropdetect and it will print out the crop settings to
-remove the borders. You should let the movie run long enough that the
-whole picture area is used, in order to get accurate crop values.
-Then, test the values you get with MPlayer, using the command line
-cropdetect printed, and adjust the rectangle as needed. The rectangle
-filter can help by allowing you to interactively position the crop
-rectangle over your movie. Remember to follow the above divisibility
-guidelines so that you do not misalign the chroma planes.
-
-If you will be scaling your movie, it's usually best to crop only the
-black borders and noise, then scale so that the resulting dimensions
-are multiples of 16. This can slightly distort the aspect ratio of
-your movie, but in practice the error cannot be seen. It's certainly
-much less visible than the MPEG artifacts you will see from failing to
-crop & scale well.
-
-In certain cases, scaling may be undesirable. Scaling in the vertical
-direction is difficult with interlaced video, and if you wish to
-preserve the interlacing, you should usually refrain from scaling. If
-you will not be scaling but you still want to use multiple-of-16
-dimensions, you will have to overcrop. Do not undercrop, since black
-borders are very bad for encoding!
-
-
-
-
-I.5. Choosing resolution and bitrate
-
-If you will not be encoding in constant quantizer mode, you need to
-select a bitrate. The concept of bitrate is quite simple. It's the
-(average) number of bits that will be consumed to store your movie,
-per second. Normally bitrate is measured in kilobits (1000 bits) per
-second. The size of your movie on disk is the bitrate times the length
-of the movie in time, plus a small amount of "overhead" (see the
-section on codecs and containers). Other parameters such as scaling,
-cropping, etc. will NOT alter the file size unless you change the
-bitrate as well!
-
-Bitrate does NOT scale proportional to resolution. That is to say, a
-320x240 file at 200 kbit/sec will not be the same quality as the same
-movie at 640x480 and 800 kbit/sec! There are two reasons for this:
-
-1. Perceptual: You notice MPEG artifacts more if they're scaled up
- bigger! Artifacts appear on the scale of blocks (8x8). Your eye
- will not see errors in 4800 small blocks as easily as it sees
- errors in 1200 large blocks (assuming you'll be scaling both to
- fullscreen).
-
-2. Theoretical: When you scale down an image but still use the same
- size (8x8) blocks for the frequency space transform, you move more
- data to the high frequency bands. Roughly speaking, each pixel
- contains more of the detail than it did before. So even though your
- scaled-down picture contains 1/4 the information in the spacial
- directions, it could still contain a large portion of the
- information in the frequency domain (assuming that the high
- frequencies were underutilized in the original 640x480 image).
-
-Past guides have recommended choosing a bitrate and resolution based
-on a "bits per pixel" approach, but this is usually not valid due to
-the above reasons. A better estimate seems to be that bitrates scale
-proportional to the square root of resolution, so that 320x240 and 400
-kbit/sec would be comparable to 640x480 at 800 kbit/sec. However this
-has not been verified with theoretical or empirical rigor. Further,
-given that movies vary greatly with regard to noise, detail, degree of
-motion, etc., it's futile to make general recommendations for bits per
-length-of-diagonal (the analogue of bits per pixel, using the square
-root).
-
-So far we have discussed the difficulty of choosing a bitrate and
-resolution.
-
-.................
-
-
-
-
-
-
-
-
-
II. Containers and codecs
@@ -364,353 +67,6 @@
ratio encoding stored in MPEG-4 avi files.
-II.2. Constraints of DVD, SVCD, and VCD
-
-Unfortunately, the DVD, SVCD, and VCD formats are subject to heavy
-constraints. Only a small selection of encoded picture sizes & aspect
-ratios are available. If your movie does not meet one of these, you
-must scale and crop or add black borders (which are bad for quality!)
-to make it compliant.
-
-Format Resolution V.Codec A.Codec FPS Aspect
-NTSC DVD 720x480 MPEG-2 AC3,PCM 24,30 4:3,16:9
-NTSC DVD 352x240 * MPEG-1 AC3,PCM 24,30 4:3
-NTSC SVCD 480x480 MPEG-2 MP2 30 4:3
-NTSC VCD 352x240 MPEG-1 MP2 24,30 4:3
-PAL DVD 720x576 MPEG-2 MP2,AC3,PCM 25 4:3,16:9
-PAL DVD 352x288 * MPEG-1 MP2,AC3,PCM 25 4:3
-PAL SVCD 480x576 MPEG-2 MP2 25 4:3
-PAL VCD 352x288 MPEG-1 MP2 25 4:3
-
-* These resolutions are rarely used in DVD because they are fairly low
- quality.
-
-DVD, VCD, and SVCD also constrain you to relatively low GOP sizes. 18 is
-supposed to be the largest allowed GOP size for 30 fps NTSCP material;
-for 25 or 24 fps, the GOP size should be 15.
-
-VCD video is required to be CBR at 1152 kbps. This highly limiting
-constraint also comes along with an extremly low vbv buffer size of
-327 kilobits. SVCD allows varying video bitrates up to 2500 kbps, and
-a somewhat less insane vbv buffer size of 917 kilobits is allowed. DVD
-video bitrates may range anywhere up to 9800 kbps (though typical bitrates
-are about half that), and the vbv buffer size is 1835 kilobits.
-
-Here is a list of fields in lavcopts that you may be required to change
-in order to make usable video for VCD, SVCD, or DVD:
-
-acodec: mp2 for VCD, SVCD, or PAL DVD; ac3 is most commonly used for DVD.
- PCM audio may also be used for DVD, but this is mostly a big
- waste of space. Note that mp3 audio isn't spec-compliant for
- any of these formats, but players often have no problem playing
- it anyway.
-
-abitrate: 224 for VCD; user-selectable for DVD and SVCD, but commonly used
- values range from 192 to 384 kbps.
-
-vcodec: mpeg1video for VCD; mpeg2video for SVCD; mpeg2video is usually
- used for DVD but you may also use mpeg1video for CIF resolutions.
-
-keyint: 18 for 30fps material, or 15 for 25/24 fps material. Commercial
- producers seem to prefer keyframe intervals of 12.
-
-vrc_buf_size: 327 for VCD, 917 for SVCD, and 1835 for DVD.
-
-vrc_minrate: 1152, for VCD. May be left alone for SVCD and DVD.
-
-vrc_maxrate: 1152 for VCD; 2500 for SVCD; 9800 for DVD. For SVCD and DVD,
- you might wish to use lower values depending on your own
- personal preferences and requirements.
-
-vbitrate: 1152 for vcd; up to 2500 for SVCD; up to 9800 for DVD. For the
- latter two formats, vbitrate should be set based on personal
- preference. For instance, if you insist on fitting 20 or so
- hours on a DVD, you could use vbitrate=400. The resulting
- video quality would probably be quite bad. If you are trying
- to squeeze out the maximum possible quality on a DVD, use
- vbitrate=9800, but be warned that this could constrain you to
- less than an hour of video on a single-layer DVD.
-
-Here is a typical minimum set of lavcopts for encoding video for a VCD:
-
--lavcopts vcodec=mpeg1video:vrc_buf_size=327:vrc_minrate=1152:\
-vrc_maxrate=1152:vbitrate=1152:keyint=15:acodec=mp2
-
-SVCD:
-
--lavcopts vcodec=mpeg2video:vrc_buf_size=917:vrc_maxrate=2500:vbitrate=1800:\
-keyint=15:acodec=mp2
-
-DVD:
-
--lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:\
-vbitrate=5000:keyint=15:acodec=ac3
-
-For higher quality encoding, you may also wish to add quality-enhancing
-options to lavcopts, such as trell, mbd=2, and others. Note that qpel
-and v4mv, while often useful with MPEG-4, are not usable in MPEG-1 or
-MPEG-2. Also, if you are trying to make a very high quality DVD encode,
-it may be useful to add dc=10 to lavcopts. Doing so may help reduce the
-appearance of blocks in flat-colored areas. Putting it all together,
-here is an example of a set of lavcopts for a higher quality DVD:
-
--lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:\
-vbitrate=8000:keyint=15:trell:mbd=2:precmp=2:subcmp=2:cmp=2:dia=-10:\
-predia=-10:cbp:mv0:vqmin=1:lmin=1:dc=10
-
-If your movie has 2.35:1 aspect (most recent action movies), you will
-have to add black borders or crop the movie down to 16:9 to make a DVD
-or VCD. If you add black borders, try to align them at 16-pixel
-boundaries in order to minimize the impact on encoding performance.
-Thankfully DVD has sufficiently excessive bitrate that you do not have
-to worry too much about encoding efficiency, but SVCD and VCD are
-highly bitrate-starved and require effort to obtain acceptable
-quality.
-
-
-
-
-
-II.3. Limitations of the AVI container
-
-Although it's the most widely-supported format after MPEG-1, AVI also
-has some major drawbacks. Perhaps the most obvious is the overhead.
-For each chunk of the AVI file, 24 bytes are wasted on headers and
-index. This translates into a little over 5 MB per hour, or 1-2.5%
-overhead for a 700 MB movie. This may not seem like much, but it could
-mean the difference between being able to use 700 kbit/sec video or
-714 kbit/sec, and every bit of quality counts.
-
-In addition to gross inefficiency, AVI also has the following major
-limitations:
-
-1. Only fixed-fps content can be stored. This is particularly limiting
- if the original material you want to encode is mixed content, for
- example a mix of NTSC video and film material. Actually there are
- hacks that can be used to store mixed-framerate content in AVI, but
- they increase the (already huge) overhead fivefold or more so they
- are not practical.
-
-2. Audio in AVI files must be either constant-bitrate (CBR) or
- constant-framesize (i.e. all frames decode to the same number of
- samples). Unfortunately, the most efficient codec, Vorbis, does not
- meet either of these requirements. Therefore, if you plan to store
- your movie in AVI, you'll have to use a less efficient codec such
- as MP3 or AC3.
-
-With all of that said, MEncoder does not support variable-fps output
-or Vorbis encoding. Therefore, you may not see these as limitations if
-MEncoder is the only tool you will be using to produce your encodes.
-However, it is possible to use MEncoder only for the video encoding,
-and then use external tools to encode the audio and mux it into
-another container format.
-
-
-
-
-
-
-
-III. Basic MEncoder usage
-
-III.1. Selecting codecs & format
-
-Audio and video codecs for encoding are selected with the -oac and
--ovc options, respectively. The following choices are available,
-although some may not have been enabled at compiletime:
-
-Audio Codecs
-mp3lame Encode VBR or CBR MP3 with LAME
-lavc Use one of libavcodec's audio encoders
-pcm Uncompressed PCM audio
-copy Do not reencode, just copy compressed frames
-
-Video codecs
-lavc Use one of libavcodec's video encoders
-xvid XviD
-raw Uncompressed video frames
-copy Do not reencode, just copy compressed frames
-frameno Used for 3-pass encoding (not recommended)
-
-Several other video codecs are available, but not recommended. The
-lavc audio and video encoders have additional suboptions to select
-which codec to use within lavc. The syntax is:
-
- -lavcopts acodec=audio_codec_name
- -lavcopts vcodec=video_codec_name
-
-Your choices for lavc audio are mp2, ac3, and various adpcm formats
-(low efficiency). For lavc video, you have many more choices:
-
-mpeg1video MPEG-1 video
-mpeg2video MPEG-2 video
-mpeg4 MPEG-4 video, standards-compliant
-msmpeg4 Pre-standard MPEG-4 used by MS (aka DivX3)
-msmpeg4v2 Pre-standard MPEG-4 used by MS (low quality)
-msmpeg4v1 Pre-standard MPEG-4 used by MS (low quality)
-wmv1 Windows Media Video, V1 (aka WMV7)
-wmv2 Windows Media Video, V2 (aka WMV8)
-dvvideo DV video (used by DV cameras)
-mjpeg Motion JPEG
-ljpeg Lossless JPEG
-ffv1 Lossless FFmpeg video codec #1 (slow)
-huffyuv A standard lossless codec
-
-...and lots more that aren't worth mentioning for most people.
-
-
-
-III.2. Selecting input file or device
-
-MEncoder can encode from files or directly from a DVD or VCD disc.
-Simply include the filename on the command line to encode from a file,
-or dvd://titlenumber or vcd://tracknumber to encode from a DVD title
-or VCD track. If you have already copied a DVD to your hard drive and
-wish to encode from the copy, you should still use the dvd:// syntax,
-along with -dvd-device followed by the path to the copied DVD root.
-The -dvd-device and -cdrom-device options can also be used to override
-the paths to the device nodes for reading directly from disc, if the
-defaults of /dev/dvd and /dev/cdrom do not work on your system.
-
-When encoding from DVD, it is often desirable to select a chapter or
-range of chapters to encode. You can use the -chapter option for this
-purpose. For example, -chapter 1-4 will only encode chapters 1 through
-4 from the DVD. This is especially useful if you will be making a 1400
-MB encode targetted for two CDs, since you can ensure the split occurs
-exactly at a chapter boundary rather than in the middle of a scene.
-
-If you have a supported TV capture card, you can also encode from the
-TV-in device. Use tv://channelnumber as the filename, and -tv to
-configure various capture settings. DVB input works similarly.
-
-
-III.3. Loading video filters
-
-Learning how to use MEncoder's video filters is essential to producing
-good encodes. All video processing is performed through the filters --
-cropping, scaling, color adjustment, noise removal, sharpening,
-deinterlacing, telecine, inverse telecine, and deblocking, just to
-name a few. Along with the vast number of supported input formats, the
-variety of filters available in MEncoder is one of its main advantages
-over other similar programs.
-
-Filters are loaded in a chain using the -vf option:
-
- -vf filter1=options,filter2=options,...
-
-Most filters take several numeric options separated by colons, but the
-syntax for options varies from filter to filter, so read the man page
-for details on the filters you wish to use.
-
-Filters operate on the video in the order they are loaded. For
-example, the following chain:
-
- -vf crop=688:464:12:4,scale=640:464
-
-will first crop the 688x464 region of the picture with upper-left
-corner at (12,4), and then scale the result down to 640x464.
-
-Certain filters need to be loaded at or near the beginning of the
-filter chain, in order to take advantage of information from the video
-decoder that will be lost or invalidated by other filters. The
-principal examples are pp (postprocessing, only when it is performing
-deblock or dering operations), spp (another postprocessor to remove
-MPEG artifacts), pullup (inverse telecine), and softpulldown (for
-converting soft telecine to hard telecine).
-
-Advanced topics in filter chains and usage information for specific
-filters will follow in chapters IV and V, as they are needed for the
-topics covered.
-
-
-
-III.4. Notes on A/V sync
-
-MEncoder's audio/video synchronization algorithms were designed with
-the intention of recovering files with broken sync. However they seem
-to cause unnecessary skipping and duplication of frames, and possibly
-slight A/V desync, when used with proper input. It is therefore
-recommended that you switch to basic A/V sync with the -mc 0 option,
-or put this in your ~/.mplayer/mencoder config file, as long as you
-are only working with good sources (DVD, TV capture, high quality
-MPEG-4 rips, etc) and not broken ASF/RM/MOV files.
-
-If you want to further guard against strange frame skips and
-duplication, you can use both -mc 0 and -noskip. This will prevent ALL
-A/V sync, and copy frames one-to-one, so you cannot use it if you will
-be using any filters that unpredictably add or drop frames, or if your
-input file has variable framerate! Therefore, using -noskip is not in
-general recommended.
-
-The so-called "three-pass" encoding which MEncoder supports has been
-reported to cause A/V desync. This will definitely happen if it is
-used in conjunction with certain filters, therefore, it is now
-recommended NOT to use three-pass mode. This feature is only left for
-compatibility purposes and for expert users who understand when it is
-safe to use and when it is not. If you have never heard of three-pass
-mode before, forget that we even mentioned it!
-
-There have also been reports of A/V desync when encoding from stdin
-with MEncoder. Do not do this! Always use a file or CD/DVD/etc device
-as input.
-
-
-
-
-
-IV.1. Encoding progressive video
-
-As long as your input video is progressive (see section I.1),
-
-
-Let's finally see a few examples:
-
- Encoding from 2:2 pulldown PAL DVD, title 1
- 2.35:1 picture aspect
- 1200 kbit/sec MPEG-4 video
- 128 kbit/sec average-bitrate MP3 audio
-
- mencoder dvd://1 -vf crop=712:432,scale=640:288 -mc 0 -oac mp3lame\
- -lameopts abr:br=128 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=1200
-
-The crop size was presumably obtained by using the cropdetect filter
-in MPlayer, or experimenting first with crop rectangles in MPlayer.
-The output framerate will be 25 fps, the same as the original DVD. It
-would be preferable to adjust the playback speed to match the original
-24 fps theatrical rate, but this is not yet possible with MEncoder.
-The options we pass to libavcodec are the bare minimum, and will yield
-relatively poor quality. We will refine then in subsequent sections.
-
-Now, a second example:
-
- Encoding from soft-telecined NTSC DVD, title 3
- 2.35:1 picture aspect
- 900 kbit/sec MPEG-4 video
- Keeping the original AC3 audio
-
- mencoder dvd://1 -vf crop=708:360,scale=640:288 -mc 0 -oac copy \
- -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=900 -ofps 23.976023976
-
-This example is very similar to the first example, except for the
--ofps option to adjust the output framerate. Unless you tell it
-otherwise, MEncoder takes its output framerate from the input
-framerate. This is reported as 29.97 fps (actually 30000/1001), or
-rather, 29.97 pairs of fields per second. But since the DVD is
-soft-telecined, 1/5 of these fields are not actually present, but
-intended to be added by the player when it telecines the movie in
-realtime. There are actually only 23.976 (24000/1001) frames per
-second. If you leave the framerate at the default, 29.97, it will
-still work, but every 4th frame will get encoded in duplicate, making
-the motion appear choppy.
-
-Finally, a comment on the number 23.976023976. You'll often see
-recommendations to use -ofps 23.976, but this is wrong. MEncoder will
-reduce 23.976 to 2997/125, which is not the same as 24000/1001. So in
-order to get the right framerate written in the output file's header,
-always use plenty of precision.
-
-
-
IV.2. Two-pass encoding
@@ -780,40 +136,3 @@
The options used are slightly different, but the process is otherwise
the same.
-
-
-
-
-IV.3. Encoding interlaced video
-
-If the movie you want to encode is interlaced (NTSC video or PAL
-video), you will need to choose whether you want to deinterlace or
-not. While deinterlacing will make your movie usable on progressive
-scan displays such a computer monitors and projectors, it comes at a
-cost: the field rate of 50 or 59.94 fields per second is halved to 25
-or 29.97 frames per second, and roughly half the information in your
-movie will be lost during scenes with significant motion.
-
-Therefore, if you are encoding for high quality archival purposes, it
-is recommended not to deinterlace. You can always deinterlace the
-movie at playback time when displaying it on progressive scan devices,
-and future players will be able to deinterlace to full fieldrate,
-interpolating 50 or 59.94 entire frames per second from the interlaced
-video.
-
-Special care must be taken when working with interlaced video:
-
-1. Crop height and y-offset must be multiples of 4.
-
-2. Any vertical scaling must be performed in interlaced mode.
-
-3. Postprocessing and denoising filters may not work as expected
- unless you take special care to operate them a field at a time, and
- they may damage the video if used incorrectly.
-
-With these things in mind, here is our first example:
-
- mencoder capture.avi -mc 0 -oac lavc -ovc lavc -lavcopts \
- vcodec=mpeg2video:vbitrate=6000:ilme:ildct:acodec=mp2:abitrate=224
-
-Note the ilme and ildct options.
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