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.