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diff --git a/DOCS/tech/encoding-guide.txt b/DOCS/tech/encoding-guide.txt deleted file mode 100644 index 0393bcbb5f..0000000000 --- a/DOCS/tech/encoding-guide.txt +++ /dev/null @@ -1,138 +0,0 @@ -Topics: - - -I. Preparing to encode - 1. Identifying source material and framerate - 2. Selecting the quality you want - 3. Constraints for efficient encoding - 4. Cropping and scaling - 5. Choosing resolution and bitrate - -II. Containers and codecs - 1. Where the movie will be played - 2. Constraints of DVD, SVCD, and VCD - 3. Limitations of AVI container - -III. Basic MEncoder usage - 1. Selecting codecs & format - 2. Selecting input file or device - 3. Loading video filters - 4. Notes on A/V sync - -IV. Encoding procedures - 1. Encoding progressive video - 2. Two-pass encoding - 3. Encoding interlaced video - 4. Deinterlacing - 5. Inverse telecine - 6. Capturing TV input - 7. Dealing with mixed-source content - 8. Low-quality & damaged sources - -V. Optimizing encoding quality - 1. Noise removal - 2. Pure quality-gain options - 3. Questionable-gain options - 4. Advanced MPEG-4 features - - - - -II. Containers and codecs - -II.1. Where the movie will be played - -Perhaps the most important factor to choosing the format in which you -will encode your movie is where you want to be able to play it. -Usually this involves a tradeoff between quality and features, since -the formats supported by the widest variety of players are also the -worst in regards to compression. - -If you want to be able to play your encode on standalone/set-top -players, your primary choices are DVD, VCD, and SVCD. There are also -extensions such as KVCD and XVCD which violate the standards but work -on many players and deliver higher quality. Modern players are -beginning to support MPEG-4 ("DivX") movies in AVI and perhaps other -containers as well, but these are often buggy and require you to -restrict your encodes to certain subsets of the full MPEG-4 -functionality. - -If you wish to be able to share your movies with Windows or Macintosh -users, without them having to install additional software, your -choices are very limited. The ancient MPEG-1 format with MP2 or PCM -audio is probably the only choice that is universally supported. -Interoperability with Windows/Mac also comes into play when deciding -how to encode and whether to scale to preserve aspect, since popular -media player applications for these systems do not honor the aspect -ratio encoding stored in MPEG-4 avi files. - - - -IV.2. Two-pass encoding - -The complexity (and thus the number of bits) required to compress the -frames of a movie can vary greatly from one scene to another. Modern -video encoders can adjust to these needs as they go and vary the -bitrate. However, they cannot exceed the requested average bitrate for -long stretches of time, because they do not know the bitrate needs of -future scenes. - -Two-pass encoding solves this problem by encoding the movie twice. -During the first pass, statistics are generated regarding the number -of bits used by each frame and the quantization level (quality) at -which it was encoded. Then, when the second pass begins, the encoder -reads these statistics and redistributes the bits from frames where -they are in excess to frames that are suffering from low quality. - -In order for the process to work properly, the encoder should be given -exactly the same sequence of frames during both passes. This means -that the same filters must be used, the same encoder parameters must -be used (with the possible exception of bitrate), and the same frame -drops and duplications (if any) must take place. - -In theory it's possible to use -oac pcm or -oac copy during the first -pass to avoid spending time encoding the audio. However, this can -result in slight variations in which frames get dropped or duplicated, -so it may be preferable to encode the audio during the first pass as -well as the second. This also allows you to examine the final audio -bitrate and filesize, and to adjust the audio or video bitrate -slightly between passes if you don't meet your target size. - -Here is an example: - - Encoding from an existing AVI file - 500 kbit/sec MPEG-4 video - 96 kbit/sec average-bitrate MP3 audio - - mencoder bar.avi -vf scale=448:336 -mc 0 -oac mp3lame -lameopts \ - abr:br=96 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=500:vpass=1 - - mencoder bar.avi -vf scale=448:336 -mc 0 -oac mp3lame -lameopts \ - abr:br=96 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=500:vpass=2 - -If you do not want to overwrite the output from the first pass when -you begin the second, you can use the -o option to choose a different -output filename. Note the addition of the vpass option in this -example. If vpass is not specified, single-pass encoding is performed. -If vpass=1, a log file is written with statistics from the first pass. -If vpass=2, the log file is read and the second pass is encoded based -on those statistics. If you are short on disk space or don't want the -extra disk wear from writing the file twice, you can use -o /dev/null -during the first pass. However, sometimes it is beneficial to watch -the first-pass file before beginning the second pass to make sure -nothing went wrong in the encoding. - -Next, an example using Xvid instead of libavcodec: - - Encoding from an existing AVI file - 500 kbit/sec MPEG-4 video - Copying the existing audio stream unmodified - - mencoder foo.avi -vf scale=320:240 -mc 0 -oac copy -ovc xvid \ - -xvidencopts bitrate=400:pass=1 - - mencoder foo.avi -vf scale=320:240 -mc 0 -oac copy -ovc xvid \ - -xvidencopts bitrate=400:pass=2 - -The options used are slightly different, but the process is otherwise -the same. |