mjpeg_howto.txt

Motion JPEG编解码器源代码

     -b 1500
        a Bitrate of 1500kBit/sec

     -n s
        the input Video norm is forced to SECAM

     -P This ensures that 2 B frames appear between adjacent I/P frames.
        Several common MPEG-1 decoders can't handle streams that do not
        have 2 B-frames between I/P frames

     -g 6 -G 20
        the encoder can dynamically change the group-of-pictures size to
        reflect scene changes. This is done by setting a maximum GOP (-G
        flag) size larger than the minimum (-g flag).  For VCDs sensible
        values might be a minimum of 9 and a maximum of 15.  For SVCD 9
        and 15 would be good values. If you only want to play it back on
        SW player you can use other min-max values.


  Example

  > lav2yuv stream*.avi | mpeg2enc -b 1500 -r 16 -4 1 -2 1 -S 630 -B 260
  -o video_n1_1500_r16_41_21_S630_B240.m1v

  lav2yuv processes all the stream files. Then mpeg2enc is given some
  options that make the encoded stream look nicer. Using -S 630 means
  that mpeg2enc marks the stream so that mplex generates a new stream
  every 630MB. One important thing is the use of the -B option which
  specifies the non-video (audio and mplex information) bitrate. The -B
  value of 260 should be fine for audio with 224kBit and mplex
  information. For further information take a look at the encoding
  scripts in the scripts directory.


  7.4.3.  MPEG1 Multiplexing Example

  Example

   >mplex sound.mp2 video.m1v -o my_video.mpg

  Puts the sound.mp2 and the video.m1v stream together to my_video.mpg.
  It only works that easy if you have CBR (the -q option was not used
  with mpeg2enc).

  Example

  mplex -V -r 1740 audio.mp2 video_vbr.m1v -o vbr_stream.mpg

  Here we multiplex a variable bitrate stream. mplex is now a single
  pass multiplexer so it can't detect the maximal bitrate and we have to
  specify it. The data rate for the output stream is: audio bitrate +
  peak videobitrate + 1-2% for mplex information. If audio (-b 224) has
  224kBit, video has 1500kBit (was encoded with -b 1500 -q 9) then we
  have 1724 * 1.01 or about 1740kBit.


  7.5.  Creating MPEG2 Videos

  MPEG2 is recommended for sources with a greater picture than 352x240
  for NTSC and 352x288 for PAL. MPEG2 can also handle interlaced sources
  like recording from TV at full resolution.

  MPEG2 allows the usage of mpeg layer 3 (mp3) sound. So you can use
  your favorite mp3encoder for the creation of the sound.  However, MP3
  audio is not valid for DVDs.  It is best to use MP2 (Layer 2) audio.
  The audio can also be a VBR Stream.
  MPEG2 is usually a VBR Stream. MPEG2 creation with optimization
  requires a lot of CPU power.  A film with the double resolution is NOT
  4 times larger than an MPEG1 Stream. Depending on your quality
  settings it will be about 1.5 up to 3 times larger than the MPEG1
  Stream at its lower resolution.

  7.5.1.  MPEG2 Audio creation Example

  > lav2wav editlist.eli | mp2enc -o sound.mp2

  This will fit the MPEG2 quite well. You can save some bits by telling
  mp2enc to use a lower bitrate (-b option) like 160 or 192 kBit/s. And
  might want to add -r 44100 so that mpeg2enc generates a 44.1kHz
  sampling rate audio file. I hope I don't need to explain the usage of
  an MP3 Encoder.  But you should not use all the fancy options that are
  available.

  7.5.2.  MPEG2 Video creation Example

  > lav2yuv editlist.eli | mpeg2enc -f 3 -b 3000 -q 9 -o video.m2v

  A very simple example for MPEG2 Video.  The most important option is
  the -f 3. That tells mpeg2enc that it should create a MPEG2 stream.
  Because it is a generic MPEG2 you have to use the -b bitrate options.
  And should use the -q option because you usually want a space saving
  VBR Stream. When using VBR streams the -b option tells mpeg2enc the
  maximum bitrate that can be used. The -q option tell mpeg2enc what
  quality the streams should have.  The bitrate has an upper bound of
  the value specified by -b.

  > lav2yuv editlist.eli | mpeg2enc -f 3 -4 1 -2 1 -q7 -b 4500 -V 300 -P
  -g 6 -G 18 -I 1 -o video.m2v

  This will generate a higher quality MPEG2 stream because the -4 1 and
  -2 1 options were used.  With -b 4500 -q 7 you tell mpeg2enc the
  maximal bitrate and the quality factor.  -V is the video buffer size
  used for decoding the stream. For SW playback it can be much higher
  than the default. Dynamic GOP is set with -g and -G.  A larger GOP
  size can help reduce the bit-rate required for a given quality but
  very large sizes can introduce artifacts due to DCT/iDCT accumulated
  rounding errors.  The -P option also ensures that 2 B frames appear
  between adjacent I/P frames. The -I 1 option tells mpeg2enc that the
  source is a interlaced material like videos. There is (time consuming)
  interlaced motion compensation logic present in mpeg2enc.  Mpeg2enc
  will use that logic if the size of the frames you encode is larger
  than the VCD size for your TV Norm.

  If you denoise the images with yuvdenoise and use the deinterlacing
  (-F) option you should tell mpeg2enc that it does not need to do
  motion estimation for interlaced material. You have to use the -I 0
  option of mpeg2enc to say that the frames are already deinterlaced.
  This will save a lot of time when encoding. If you don't use -I 0 it
  will not cause problems, the encoding will just take longer.

  You can also use scaling an options that optimize (denoise) the images
  to get smaller streams.  These options are explained in detail in the
  following sections.

  7.5.2.1.  Which values should be used for VBR Encoding

  The -q option controls the minimum quantization of the output stream.
  Quantization controls the precision with which image information is
  encoded. The lower the value the better the image quality.  Values
  below 4 are extremes and should only be used if you know what you are
  doing

  Usually you have to set up a maximum bitrate with the -b option.  The
  tricky task is to set a value for the -q option and the -b option that
  produces a nice movie without using too much bandwidth and does not
  introduce too many artifacts.

  A quality factor should be chosen that way that the mplex output of
  Peak bit-rate and average bit-rate differ by about 20-25%.  If the
  difference is very small (less than < 10%) it is likely that you will
  begin to see artifacts in high motion scenes.  The most common cause
  of the average rate being too close (or equal) to the maximum rate is
  wrong value for the maximal bitrate or a quality factor that is too
  high.

  A combination that will produce more artifacts than you can count is a
  SVCD with a maximal video bitrate of 2500kBit and a qualitfactor set
  to 1 or 2.  For SVCD with a video limit of 2500kBit a quality factor
  of 7-11 fits quite good (8 is the default). If you use filter programs
  or have a very good source like digital TV, DVD like material or
  rendered pictures you can use a quality factor of 6 when creating
  SVCDs.  If your SVCD/DVD player supports higher bitrates than the
  official 2788kBit/sec for the video and audio.   When using a higher
  bitrate and quality factor action scenes will look much better but of
  course the playing time of the disc will be less.

  The same (7-11) quality factor for a full size picture and a top
  bitrate of 3500 to 4000 kBit will produce few artifacts.

  For SVCD/DVD you can expect a result like the one described if the
  maximal bitrate is not set too low:



     q <= 6 real sharp pictures, and good quality
     q <= 8 good quality
     q >= 10 average quality
     q >= 11 not that good
     q >= 13 here even still sequences might look blocky



  7.5.2.2.  Encoding destination TV (interlaced) or Monitor (progres-
  sive)

  MPEG2 supports interlaced data in addition to the progressive format.
  A MPEG2 movie can be interlaced or progressive. It depends on the
  source (film or broadcast) and on the viewing device.

  If you encode a film both fields should be the same. Deinterlace the
  stream with yuvdenoise -F, or if you have a high quality source, and
  don't need to use the denoiser, with yuvcorrect -T NOT_INTERLACED.
  Also set the mpeg2enc interlace-mode (-I) option to 0. This means that
  there is no interlacing.  We do not really need deinterlacing here
  because there is no motion between the fields of the frame. We only
  need to unite the two fields into a single progressive frame.

  This movie should play back an any device (TV or Monitor) without
  problems.

  If you have an interlaced source (broadcast) you can encode it as
  interlaced stream. Or deinterlace the stream and encode it as
  progressive stream. If you deinterlace it with yuvdenoise -F, you will
  lose details.  But if you plan to play the recorded stream on your DVD
  player and your TV it would not be wise to perform deinterlacing.  If
  you only want to play it back on the Monitor (progressive display) the
  picture looks better when playing it back if it is deinterlaced. If
  the player you use can do deinterlacing it does not matter if your
  encoded video has interlaced frames or progressive frames.

  If you plan to deinterlace the stream you can only do this with
  yuvdenoise -F, and set the mpeg2enc -I 0. If you do not want to
  deinterlace the stream you do not need to set any special option (do
  not use yuvdenoise -F and mpeg2enc -I 0)

  If you like to pause the stream and look on the still you should
  deinterlace. Because then the image is flicker free when pausing.

  If you have a film (progressive) with parts from a broadcast
  (interlaced) mixed together (like in a documentary where some parts
  from a speaker are recorded interlaced and other parts are filmed) you
  have to choose between good film sequences with average still images
  or average looking film sequences with good still images.

  For good film with average stills do not deinterlace.  For average
  film sequences with good stills then deinterlace (using -F and -I 0).

  7.5.3.  MPEG2 Multiplexing Example

  > mplex -f 3 -b 300 -r 4750 -V audio.mp3 video.mp3 -o final.mpg

  Now both streams (a mp3 audio and a mpeg2 video) are multiplex into a
  single stream (final.mpg). You have to use the -f 3 option to tell
  mplex the output format. You also have to add the -b decoder buffers
  size with the same value used when encoding the video. -r is that rate
  of video + audio +1-2% of mplex information.

  The -V option tells that your source for mplexing is a VBR stream. If
  you don't use this option mplex creates something like a CBR Stream
  with the bitrate you have told it with the -r option.  These streams
  are usually get BIG.



  7.6.  Creating Video-CD's

  VCD is a constrained version of MEPG1 streams.  VCD format was defined
  by Philips. The goal was to use a single speed CD-drive and other
  cheap hardware (not flexible) to have a cheap HW-Player.  Because of
  that there are some limitations on VCD's.  The bitrate for video is
  1152kBit and for audio layer 2 audio 224kBit stereo.  You are not
  allowed to use the -q option, dynamic GOP sizes and the video buffer
  is limited to 46kB.  The image size is limited to 352x240 for NTSC, an
  to 352x288 for PAL.

  If you have no VCD (only) player and you plan to use your DVD player
  then it is quite possible that the DVD player will be flexible enough
  to allow higher bitrates, dynamic GOP sizes, larger video buffer and
  so on

  7.6.1.  VCD Audio creation Example

  > lav2wav stream.avi | mp2enc -V -o sound.mp2

  -V force VCD 2.0 compatible output.  There the audio samplerate is
  fixed to 44.1kHz. And  you can choose the audio bitrate for mono audio
  to be 64, 96 or 192kBit/sec. If you have stereo audio you can choose
  128, 192, 224 or 384kBit/sec.  For hardware players, you should stick
  to 44.1 224kBps Stereo layer 2 Audio.

  7.6.2.  VCD Video creation Example

  > lav2yuv stream.avi | yuvscaler -O VCD | mpeg2enc -f 1 -r 16 -o
  video.mpg
  For a VCD compatible output the -f 1 sets all options in mpeg2enc as
  needed. It seems that many VCD players (Avex for example) are not able
  to play MPEG streams that are encoded with a search radius greater
  than 16 so do not use the -r option to override the default of 16.

  > lav2yuv streams.eli | mpeg2enc -f 1 -4 1 -2 1 -S 630 -B 260 -P -o
  video.m1v

  Using '-S 630' means that mpeg2enc marks the stream so that mplex
  generates a new stream every 630MB. One important thing is the use of
  the -B option which specifies the non-video (audio and mplex
  information) bitrate. The -B value of 260 should be fine for audio
  with 224kBit and mplex information. For further information take a
  look at the encoding scripts in the scripts directory. So the
  multiplexed streams should easily fit on a CD with 650MB.

  The default value (-B) is 700MB for the video. mpeg2enc marks
  automatically every stream at that size if the -B option is not used
  to set a different value.  If you have a CD where you can write more
  data (perhaps as much as 800MB), you have to set the -S option or
  otherwise mpeg2enc will mark the stream at 700 MB, and mplex will
  split the stream there.  Which is almost certainly not what you want.



  7.6.3.  VCD Multiplexing Example

  > mplex -f 1 sound.mp2 video.mpg -o vcd_out.mpg

  The -f 1 option turns on a lot of weird stuff that otherwise has no
  place in a respectable multiplexer!

  7.6.4.  Creating the CD

  The multiplexed streams have to be converted to an VCD compatible.
  This is done by vcdimager http://www.vcdimager.org/


  > vcdimager testvideo.mpg

  Creates a videocd.bin, the data file, and a videocd.cue which is used
  as control file for cdrdao.

  You use cdrdao to burn the image. Cdrdao is yet another fine
  Sourceforge project which is found at: http://cdrdao.sourceforge.net/

  7.6.5.  Notes

  For MPEG-1 encoding a typical (45 minute running time) show or 90 odd
  minute movie from an analog broadcast a constant bit-rate of around
  1800 kBit/sec should be ideal. The resulting files are around 700M for
  45 minutes which fits nicely as a raw XA MODE2 data track on a CD-R.
  For pure digital sources (DTV or DVD streams and similar) VCD 1152
  works fine.

  Note: If you encode VBR MPEG1 (-q) remember the Hardware was probably
  not designed to do the playback because it is not in the
  specifications. If it works be very happy. I've noticed that it helps
  when you have an MPEG1 Stream to tell vcdimager that it is an SVCD.
  vcdimager complains (but only with a warning and not a fatal error)
  but you should be able to burn it. This could convince the player to
  use different routines in its firmware and play it back correct, but
  there is no guarantee of that.



  7.6.6.  Storing MPEGs

  If you record the data as XA mode 2 tracks you can fit appreciably
  more on a CD (at the expense of error correction/detection). You can
  use vcdimager to do this and vcdxrip (part of the vcdimager package)
  to extract ("rip") the resulting files. For better Quality there are
  SVCD and XVCD and DVD.

  Currently SVCD is fully supported with a pre-set format in mplex and
  tools to create disks. MPEG streams that can be played by DVD player
  hardware and software can readily produced using mpeg2enc/mplex

  If your player do