[vlc] x264 Encode Keyframes and Defaults

[George Bray]

I'm using VLC to transcode MPEG2-TS files to H.264 and it's working  
well.  My only complaint is that often, the first five seconds of the  
target file are all mosaic (like a Monet painting).  It seems as if  
the frequency of key frames isn't high enough, so I'm wondering which  
of the x264 settings can help me.

These ones?  What's a good value?

       --sout-x264-keyint <integer>
                                  Sets maximum interval between IDR- 
frames

       --sout-x264-scenecut <integer>
                                  Scene-cut detection.

The VLC longhelp is great, but it would be very helpful if all the  
default values (and expected ranges) could be provided for these  
parameters.

thanks very much,

George
University of Canberra, Australia



H264 encoder (using x264 library)
       --sout-x264-qp <integer>   Quantizer parameter
           This selects the quantizer to use (1 to 51). Lower values  
result in better fidelity, but higher bitrates. 26 is a good default
           value.
       --sout-x264-qp-min <integer>
                                  Minimum quantizer parameter
           Minimum quantizer, 15/35 seems to be a useful range.
       --sout-x264-qp-max <integer>
                                  Maximum quantizer parameter
           Maximum quantizer parameter.
       --sout-x264-cabac, --no-sout-x264-cabac
                                  Enable CABAC (default enabled)
           Enable CABAC (Context-Adaptive Binary Arithmetic Coding).  
Slightly slows down encoding and decoding, but should save 10-15%
           bitrate. (default enabled)
       --sout-x264-loopfilter, --no-sout-x264-loopfilter
                                  Enable loop filter (default enabled)
           Use deblocking loop filter (increases quality). (default  
enabled)
       --sout-x264-analyse {,all,normal,fast,none}
                                  Analyse mode
           This selects the analysing mode.
       --sout-x264-tolerance <float>
                                  Bitrate tolerance
           Sets the allowed variance in average bitrate.
       --sout-x264-vbv-maxrate <integer>
                                  Maximum local bitrate
           Sets a maximum local bitrate in kbits/s.
       --sout-x264-vbv-bufsize <integer>
                                  Averaging period for the maximum  
local bitrate
           Sets an averaging period for the maximum local bitrate, in  
kbits/s.
       --sout-x264-vbv-init <float>
                                  Initial buffer occupancy
           Sets the initial buffer occupancy as a fraction of the  
buffer size.
       --sout-x264-keyint <integer>
                                  Sets maximum interval between IDR- 
frames
           Larger values save bits, thus improve quality for a given  
bitrate, at the cost of seeking precision.
       --sout-x264-keyint-min <integer>
                                  Sets minimum interval between IDR- 
frames
           In H.264, I-Frames do not necessarily bound a closed GOP  
because it is allowable for a P-frame to be predicted from more frames
           than just the one frame before it (also see frameref).  
Therefore, I-frames are not necessarily seekable. IDR-Frames restrict
           subsequent P-frames from referring to any frame prior to  
the IDR-Frame.
If scenecuts appear within this interval, they are still
           encoded as I-frames, but do not start a new GOP. Default  
value is keyint * 0.4.
       --sout-x264-bframes <integer>
                                  B frames
           Number of consecutive B-Frames between I and P-frames.
       --sout-x264-bpyramid, --no-sout-x264-bpyramid
                                  B pyramid (default disabled)
           Allows B-frames to be used as references for predicting  
other frames. (default disabled)
       --sout-x264-frameref <integer>
                                  Number of previous frames used as  
predictors.
           This is effective in Anime, but seems to make little  
difference in live-action source material. Some decoders are unable  
to deal
           with large frameref values.
       --sout-x264-scenecut <integer>
                                  Scene-cut detection.
           Controls how aggressively to insert extra I-frames. With  
small values of scenecut, the codec often has to force an I-frame  
when it
           would exceed keyint. Good values of scenecut may find a  
better location for the I-frame. Large values use more I-frames than
           necessary, thus wasting bits. -1 disables scene-cut  
detection, so I-frames are be inserted only every other keyint  
frames, which
           probably leads to ugly encoding artifacts.
       --sout-x264-subpel <integer>
                                  Sub-pixel refinement quality.
           This parameter controls quality versus speed tradeoffs  
involved in the motion estimation decision process (lower = quicker and
           higher = better quality).
       --sout-x264-me {,dia,hex,umh,esa}
                                  Motion estimation algorithm.
           Selects the motion estimation algorithm:  - dia: diamond  
search, radius 1 (fast)
- hex: hexagonal search, radius 2
- umh: uneven
           multi-hexagon search (better but slower)
- esa: exhaustive search (extremely slow, primarily for testing)

       --sout-x264-merange <integer>
                                  Motion estimation search range.
           Maximum distance to search for motion estimation, measured  
from predicted position(s). Default of 16 is good for most footage, high
           motion sequences may benefit from settings between 24-32.
       --sout-x264-no-psnr, --no-sout-x264-no-psnr
                                  Disable PSNR calculation. (default  
disabled)
           This has no effect on actual encoding quality, it just  
prevents the stats from being calculated (for speed). (default disabled)
       --sout-x264-weightb, --no-sout-x264-weightb
                                  Weighted prediction for B-frames.  
(default disabled)
           Weighted prediction for B-frames. (default disabled)
       --sout-x264-no-b-adapt, --no-sout-x264-no-b-adapt
                                  Disable adaptive B-frames. (default  
disabled)
           If this is on, the specified number of consecutive B- 
frames will always be used, except possibly before an I-frame.  (default
           disabled)
       --sout-x264-b-bias <integer>
                                  Bias the choice to use B-frames.
           Positive values cause more B-frames, negative values cause  
less B-frames.
       --sout-x264-mixed-refs, --no-sout-x264-mixed-refs
                                  Decide references on a per  
partition basis. (default disabled)
           Decide references on a per partition basis. (default  
disabled)
       --sout-x264-crf <integer>  CRF (1-pass Quality-based VBR  
(nominal QP)).
           CRF (1-pass Quality-based VBR (nominal QP)).
       --sout-x264-trellis <integer>
                                  Trellis RD quantization.
           Trellis RD quantization. Requires CABAC.
- 0: disabled
- 1: enabled only on the final encode of a MB
- 2: enabled on all mode
           decisions

       --sout-x264-b-rdo, --no-sout-x264-b-rdo
                                  RD based mode decision for B- 
frames. (default disabled)
           RD based mode decision for B-frames. Requires subme 6.  
(default disabled)
       --sout-x264-no-fast-pskip, --no-sout-x264-no-fast-pskip
                                  Disable early SKIP detection on P- 
frames. (default disabled)
           Disable early SKIP detection on P-frames. (default disabled)

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