Recherche avancée

Sur d’autres sites (14025)

• lavfi/delogo : use weighted interpolation

  26 juin 2013, par Jean Delvare

  lavfi/delogo : use weighted interpolation
  The original delogo algorithm interpolates both horizontally and
  
  vertically and uses the average to compute the resulting sample. This
  
  works reasonably well when the logo area is almost square. However
  
  when the logo area is significantly larger than high or higher than
  
  large, the result is largely suboptimal.
  The issue can be clearly seen by testing the delogo filter with a fake
  
  logo area that is 200 pixels large and 2 pixels high. Vertical
  
  interpolation gives a very good result in that case, horizontal
  
  interpolation gives a very bad result, and the overall result is poor,
  
  because both are given the same weight.
  Even when the logo is roughly square, the current algorithm gives poor
  
  results on the borders of the logo area, because it always gives
  
  horizontal and vertical interpolations an equal weight, and this is
  
  suboptimal on borders. For example, in the middle of the left hand
  
  side border of the logo, you want to trust the left known point much
  
  more than the right known point (which the current algorithm already
  
  does) but also much more than the top and bottom known points (which
  
  the current algorithm doesn’t do.)
  By properly weighting each known point when computing the value of
  
  each interpolated pixel, the visual result is much better, especially
  
  on borders and/or for high or large logo areas.
  The algorithm I implemented guarantees that the weight of each of the
  
  4 known points directly depends on its distance to the interpolated
  
  point. It is largely inspired from the original algorithm, the key
  
  difference being that it computes the relative weights globally
  
  instead of separating the vertical and horizontal interpolations and
  
  combining them afterward.
  Signed-off-by : Jean Delvare <khali@linux-fr.org>
  
  Signed-off-by : Stefano Sabatini <stefasab@gmail.com>
  

  • [DH] libavfilter/vf_delogo.c
  • [DH] tests/ref/fate/filter-delogo

• Revision a49d80bfc8 : Squash commits from master to playground Moving RD-opt related code from vp9_en

  26 juin 2014, par Yue Chen

  Changed Paths :
   Modify /build/make/gen_msvs_proj.sh

  
   Modify /build/make/gen_msvs_vcxproj.sh

  
   Modify /build/make/iosbuild.sh

  
   Modify /examples/vp9_spatial_svc_encoder.c

  
   Modify /test/decode_test_driver.cc

  
   Modify /test/decode_test_driver.h

  
   Add /test/invalid_file_test.cc

  
   Modify /test/svc_test.cc

  
   Modify /test/test-data.sha1

  
   Modify /test/test.mk

  
   Modify /test/test_vectors.cc

  
   Add /test/user_priv_test.cc

  
   Add /third_party/libmkv/EbmlIDs.h

  
   Add /third_party/libmkv/EbmlWriter.c

  
   Add /third_party/libmkv/EbmlWriter.h

  
   Modify /vp8/common/rtcd_defs.pl

  
   Modify /vp8/encoder/x86/quantize_sse2.c

  
   Delete /vp8/encoder/x86/quantize_sse4.asm

  
   Add /vp8/encoder/x86/quantize_sse4.c

  
   Modify /vp8/vp8cx.mk

  
   Modify /vp9/common/arm/neon/vp9_convolve_neon.c

  
   Modify /vp9/common/arm/neon/vp9_loopfilter_16_neon.c

  
   Modify /vp9/common/vp9_alloccommon.c

  
   Modify /vp9/common/vp9_alloccommon.h

  
   Modify /vp9/common/vp9_convolve.c

  
   Modify /vp9/common/vp9_mvref_common.c

  
   Modify /vp9/common/vp9_mvref_common.h

  
   Modify /vp9/common/vp9_quant_common.c

  
   Modify /vp9/common/vp9_quant_common.h

  
   Modify /vp9/common/vp9_scale.h

  
   Modify /vp9/decoder/vp9_decodeframe.c

  
   Modify /vp9/decoder/vp9_decoder.c

  
   Modify /vp9/decoder/vp9_dthread.h

  
   Modify /vp9/decoder/vp9_read_bit_buffer.c

  
   Modify /vp9/encoder/vp9_bitstream.c

  
   Modify /vp9/encoder/vp9_block.h

  
   Modify /vp9/encoder/vp9_denoiser.c

  
   Modify /vp9/encoder/vp9_denoiser.h

  
   Modify /vp9/encoder/vp9_encodeframe.c

  
   Modify /vp9/encoder/vp9_encoder.c

  
   Modify /vp9/encoder/vp9_encoder.h

  
   Modify /vp9/encoder/vp9_firstpass.c

  
   Modify /vp9/encoder/vp9_firstpass.h

  
   Modify /vp9/encoder/vp9_lookahead.c

  
   Modify /vp9/encoder/vp9_lookahead.h

  
   Modify /vp9/encoder/vp9_pickmode.c

  
   Modify /vp9/encoder/vp9_pickmode.h

  
   Modify /vp9/encoder/vp9_ratectrl.c

  
   Modify /vp9/encoder/vp9_ratectrl.h

  
   Modify /vp9/encoder/vp9_rdopt.c

  
   Modify /vp9/encoder/vp9_rdopt.h

  
   Modify /vp9/encoder/vp9_speed_features.c

  
   Modify /vp9/encoder/vp9_speed_features.h

  
   Modify /vp9/encoder/vp9_svc_layercontext.c

  
   Modify /vp9/encoder/vp9_svc_layercontext.h

  
   Modify /vp9/vp9_cx_iface.c

  
   Modify /vp9/vp9_dx_iface.c

  
   Modify /vp9/vp9cx.mk

  
   Modify /vpx/src/svc_encodeframe.c

  
   Modify /vpx/svc_context.h

  
  
  Squash commits from master to playground

  Moving RD-opt related code from vp9_encoder.h to vp9_rdopt.h.

  Squashed-Change-Id : I8fab776c8801e19d3f5027ed55a6aa69eee951de

  gen_msvs_proj : fix in tree configure under cygwin

  strip trailing ’/’ from paths, this is later converted to ’\’ which
  causes execution errors for obj_int_extract/yasm. vs10+ wasn’t affected
  by this issue, but make the same change for consistency.

  gen_msvs_proj :
  + add missing ’"’ to obj_int_extract call
  unlike gen_msvs_vcproj, the block is duplicated
  missed in : 1e3d9b9 build/msvs : fix builds in source dirs with spaces

  Squashed-Change-Id : I76208e6cdc66dc5a0a7ffa8aa1edbefe31e4b130

  Improve vp9_rb_bytes_read

  Squashed-Change-Id : I69eba120eb3d8ec43b5552451c8a9bd009390795

  Removing decode_one_iter() function.

  When superframe index is available we completely rely on it and use frame
  size values from the index.

  Squashed-Change-Id : I0011d08b223303a8b912c2bcc8a02b74d0426ee0

  iosbuild.sh : Add vpx_config.h and vpx_version.h to VPX.framework.

   Rename build_targets to build_framework
   Add functions for creating the vpx_config shim and obtaining
  preproc symbols.

  Squashed-Change-Id : Ieca6938b9779077eefa26bf4cfee64286d1840b0

  Implemented vp9_denoiser_alloc,free()

  Squashed-Change-Id : I79eba79f7c52eec19ef2356278597e06620d5e27

  Update running avg for VP9 denoiser

  Squashed-Change-Id : I9577d648542064052795bf5770428fbd5c276b7b

  Changed buf_2ds in vp9 denoiser to YV12 buffers

  Changed alloc, free, and running average code as necessary.

  Squashed-Change-Id : Ifc4d9ccca462164214019963b3768a457791b9c1

  sse4 regular quantize

  Squashed-Change-Id : Ibd95df0adf9cc9143006ee9032b4cb2ebfd5dd1b

  Modify non-rd intra mode checking

  Speed 6 uses small tx size, namely 8x8. max_intra_bsize needs to
  be modified accordingly to ensure valid intra mode checking.
  Borg test on RTC set showed an overall PSNR gain of 0.335% in speed
   6.

  This also changes speed -5 encoding by allowing DC_PRED checking
  for block32x32. Borg test on RTC set showed a slight PSNR gain of
  0.145%, and no noticeable speed change.

  Squashed-Change-Id : I1502978d8fbe265b3bb235db0f9c35ba0703cd45

  Implemented COPY_BLOCK case for vp9 denoiser

  Squashed-Change-Id : Ie89ad1e3aebbd474e1a0db69c1961b4d1ddcd33e

  Improved vp9 denoiser running avg update.

  Squashed-Change-Id : Ie0aa41fb7957755544321897b3bb2dd92f392027

  Separate rate-distortion modeling for DC and AC coefficients

  This is the first step to rework the rate-distortion modeling used
  in rtc coding mode. The overall goal is to make the modeling
  customized for the statistics encountered in the rtc coding.

  This commit makes encoder to perform rate-distortion modeling for
  DC and AC coefficients separately. No speed changes observed.
  The coding performance for pedestrian_area_1080p is largely
  improved :

  speed -5, from 79558 b/f, 37.871 dB -> 79598 b/f, 38.600 dB
  speed -6, from 79515 b/f, 37.822 dB -> 79544 b/f, 38.130 dB

  Overall performance for rtc set at speed -6 is improved by 0.67%.

  Squashed-Change-Id : I9153444567e5f75ccdcaac043c2365992c005c0c

  Add superframe support for frame parallel decoding.

  A superframe is a bunch of frames that bundled as one frame. It is mostly
  used to combine one or more non-displayable frames and one displayable frame.

  For frame parallel decoding, libvpx decoder will only support decoding one
  normal frame or a super frame with superframe index.

  If an application pass a superframe without superframe index or a chunk
  of displayable frames without superframe index to libvpx decoder, libvpx
  will not decode it in frame parallel mode. But libvpx decoder still could
  decode it in serial mode.

  Squashed-Change-Id : I04c9f2c828373d64e880a8c7bcade5307015ce35

  Fixes in VP9 alloc, free, and COPY_FRAME case

  Squashed-Change-Id : I1216f17e2206ef521fe219b6d72d8e41d1ba1147

  Remove labels from quantize

  Use break instead of goto for early exit. Unbreaks Visual Studio
  builds.

  Squashed-Change-Id : I96dee43a3c82145d4abe0d6a99af6e6e1a3991b5

  Added CFLAG for outputting vp9 denoised signal

  Squashed-Change-Id : Iab9b4e11cad927f3282e486c203564e1a658f377

  Allow key frame more flexibility in mode search

  This commit allows the key frame to search through more prediction
  modes and more flexible block sizes. No speed change observed. The
  coding performance for rtc set is improved by 1.7% for speed -5 and
  3.0% for speed -6.

  Squashed-Change-Id : Ifd1bc28558017851b210b4004f2d80838938bcc5

  VP9 denoiser bugfixes

  s/stdint.h/vpx\/vpx_int.h

  Added missing ’break ;’s

  Also included other minor changes, mostly cosmetic.

  Squashed-Change-Id : I852bba3e85e794f1d4af854c45c16a23a787e6a3

  Don’t return value for void functions

  Clears "warning : ’return’ with a value, in function returning void"

  Squashed-Change-Id : I93972610d67e243ec772a1021d2fdfcfc689c8c2

  Include type defines

  Clears error : unknown type name ’uint8_t’

  Squashed-Change-Id : I9b6eff66a5c69bc24aeaeb5ade29255a164ef0e2

  Validate error checking code in decoder.

  This patch adds a mechanism for insuring error checking on invalid files
  by creating a unit test that runs the decoder and tests that the error
  code matches what’s expected on each frame in the decoder.

  Disabled for now as this unit test will segfault with existing code.

  Squashed-Change-Id : I896f9686d9ebcbf027426933adfbea7b8c5d956e

  Introduce FrameWorker for decoding.

  When decoding in serial mode, there will be only
  one FrameWorker doing decoding. When decoding in
  parallel mode, there will be several FrameWorkers
  doing decoding in parallel.

  Squashed-Change-Id : If53fc5c49c7a0bf5e773f1ce7008b8a62fdae257

  Add back libmkv ebml writer files.

  Another project in ChromeOS is using these files. To make libvpx
  rolls simpler, add these files back unitl the other project removes
  the dependency.

  crbug.com/387246 tracking bug to remove dependency.

  Squashed-Change-Id : If9c197081c845c4a4e5c5488d4e0190380bcb1e4

  Added Test vector that tests more show existing frames.

  Squashed-Change-Id : I0ddd7dd55313ee62d231ed4b9040e08c3761b3fe

  fix peek_si to enable 1 byte show existing frames.

  The test for this is in test vector code ( show existing frames will
  fail ). I can’t check it in disabled as I’m changing the generic
  test code to do this :

  https://gerrit.chromium.org/gerrit/#/c/70569/

  Squashed-Change-Id : I5ab324f0cb7df06316a949af0f7fc089f4a3d466

  Fix bug in error handling that causes segfault

  See : https://code.google.com/p/chromium/issues/detail?id=362697

  The code properly catches an invalid stream but seg faults instead of
  returning an error due to a buffer not having been initialized. This
  code fixes that.

  Squashed-Change-Id : I695595e742cb08807e1dfb2f00bc097b3eae3a9b

  Revert 3 patches from Hangyu to get Chrome to build :

  Avoids failures :
  MSE_ClearKey/EncryptedMediaTest.Playback_VP9Video_WebM/0
  MSE_ClearKey_Prefixed/EncryptedMediaTest.Playback_VP9Video_WebM/0
  MSE_ExternalClearKey_Prefixed/EncryptedMediaTest.Playback_VP9Video_WebM/0
  MSE_ExternalClearKey/EncryptedMediaTest.Playback_VP9Video_WebM/0
  MSE_ExternalClearKeyDecryptOnly/EncryptedMediaTest.Playback_VP9Video_WebM/0
  MSE_ExternalClearKeyDecryptOnly_Prefixed/EncryptedMediaTest.Playback_VP9Video_We
  bM/0
  SRC_ExternalClearKey/EncryptedMediaTest.Playback_VP9Video_WebM/0
  SRC_ExternalClearKey_Prefixed/EncryptedMediaTest.Playback_VP9Video_WebM/0
  SRC_ClearKey_Prefixed/EncryptedMediaTest.Playback_VP9Video_WebM/0

  Patches are
  This reverts commit 9bc040859b0ca6869d31bc0efa223e8684eef37a
  This reverts commit 6f5aba069a2c7ffb293ddce70219a9ab4a037441
  This reverts commit 9bc040859b0ca6869d31bc0efa223e8684eef37a

  I1f250441 Revert "Refactor the vp9_get_frame code for frame parallel."
  Ibfdddce5 Revert "Delay decreasing reference count in frame-parallel
  decoding."
  I00ce6771 Revert "Introduce FrameWorker for decoding."

  Need better testing in libvpx for these commits

  Squashed-Change-Id : Ifa1f279b0cabf4b47c051ec26018f9301c1e130e

  error check vp9 superframe parsing

  This patch insures that the last byte of a chunk that contains a
  valid superframe marker byte, actually has a proper superframe index.
  If not it returns an error.

  As part of doing that the file : vp90-2-15-fuzz-flicker.webm now fails
  to decode properly and moves to the invalid file test from the test
  vector suite.

  Squashed-Change-Id : I5f1da7eb37282ec0c6394df5c73251a2df9c1744

  Remove unused vp9_init_quant_tables function

  This function is not effectively used, hence removed.

  Squashed-Change-Id : I2e8e48fa07c7518931690f3b04bae920cb360e49

  Actually skip blocks in skip segments in non-rd encoder.

  Copy split from macroblock to pick mode context so it doesn’t get lost.

  Squashed-Change-Id : Ie37aa12558dbe65c4f8076cf808250fffb7f27a8

  Add Check for Peek Stream validity to decoder test.

  Squashed-Change-Id : I9b745670a9f842582c47e6001dc77480b31fb6a1

  Allocate buffers based on correct chroma format

  The encoder currently allocates frame buffers before
  it establishes what the chroma sub-sampling factor is,
  always allocating based on the 4:4:4 format.

  This patch detects the chroma format as early as
  possible allowing the encoder to allocate buffers of
  the correct size.

  Future patches will change the encoder to allocate
  frame buffers on demand to further reduce the memory
  profile of the encoder and rationalize the buffer
  management in the encoder and decoder.

  Squashed-Change-Id : Ifd41dd96e67d0011719ba40fada0bae74f3a0d57

  Fork vp9_rd_pick_inter_mode_sb_seg_skip

  Squashed-Change-Id : I549868725b789f0f4f89828005a65972c20df888

  Switch active map implementation to segment based.

  Squashed-Change-Id : Ibb841a1fa4d08d164cf5461246ec290f582b1f80

  Experiment for mid group second arf.

  This patch implements a mechanism for inserting a second
  arf at the mid position of arf groups.

  It is currently disabled by default using the flag multi_arf_enabled.

  Results are currently down somewhat in initial testing if
  multi-arf is enabled. Most of the loss is attributable to the
  fact that code to preserve the previous golden frame
  (in the arf buffer) in cases where we are coding an overlay
  frame, is currently disabled in the multi-arf case.

  Squashed-Change-Id : I1d777318ca09f147db2e8c86d7315fe86168c865

  Clean out old CONFIG_MULTIPLE_ARF code.

  Remove the old experimental multi arf code that was under
  the flag CONFIG_MULTIPLE_ARF.

  Squashed-Change-Id : Ib24865abc11691d6ac8cb0434ada1da674368a61

  Fix some bugs in multi-arf

  Fix some bugs relating to the use of buffers
  in the overlay frames.

  Fix bug where a mid sequence overlay was
  propagating large partition and transform sizes into
  the subsequent frame because of :-
  sf->last_partitioning_redo_frequency > 1 and
  sf->tx_size_search_method == USE_LARGESTALL

  Squashed-Change-Id : Ibf9ef39a5a5150f8cbdd2c9275abb0316c67873a

  Further dual arf changes : multi_arf_allowed.

  Add multi_arf_allowed flag.
  Re-initialize buffer indices every kf.
  Add some const indicators.

  Squashed-Change-Id : If86c39153517c427182691d2d4d4b7e90594be71

  Fixed VP9 denoiser COPY_BLOCK case

  Now copies the src to the correct location in the running average buffer.

  Squashed-Change-Id : I9c83c96dc7a97f42c8df16ab4a9f18b733181f34

  Fix test on maximum downscaling limits

  There is a normative scaling range of (x1/2, x16)
  for VP9. This patch fixes the maximum downscaling
  tests that are applied in the convolve function.

  The code used a maximum downscaling limit of x1/5
  for historic reasons related to the scalable
  coding work. Since the downsampling in this
  application is non-normative it will revert to
  using a separate non-normative scaler.

  Squashed-Change-Id : Ide80ed712cee82fe5cb3c55076ac428295a6019f

  Add unit test to test user_priv parameter.

  Squashed-Change-Id : I6ba6171e43e0a43331ee0a7b698590b143979c44

  vp9 : check tile column count

  the max is 6. there are assumptions throughout the decode regarding
  this ; fixes a crash with a fuzzed bitstream

  $ zzuf -s 5861 -r 0.01:0.05 -b 6- \
  < vp90-2-00-quantizer-00.webm.ivf \
  | dd of=invalid-vp90-2-00-quantizer-00.webm.ivf.s5861_r01-05_b6-.ivf \
  bs=1 count=81883

  Squashed-Change-Id : I6af41bb34252e88bc156a4c27c80d505d45f5642

  Adjust arf Q limits with multi-arf.

  Adjust enforced minimum arf Q deltas for non primary arfs
  in the middle of an arf/gf group.

  Squashed-Change-Id : Ie8034ffb3ac00f887d74ae1586d4cac91d6cace2

  Dual ARF changes : Buffer index selection.

  Add indirection to the section of buffer indices.
  This is to help simplify things in the future if we
  have other codec features that switch indices.

  Limit the max GF interval for static sections to fit
  the gf_group structures.

  Squashed-Change-Id : I38310daaf23fd906004c0e8ee3e99e15570f84cb

  Reuse inter prediction result in real-time speed 6

  In real-time speed 6, no partition search is done. The inter
  prediction results got from picking mode can be reused in the
  following encoding process. A speed feature reuse_inter_pred_sby
  is added to only enable the resue in speed 6.

  This patch doesn’t change encoding result. RTC set tests showed
  that the encoding speed gain is 2% - 5%.

  Squashed-Change-Id : I3884780f64ef95dd8be10562926542528713b92c

  Add vp9_ prefix to mv_pred and setup_pred_block functions

  Make these two functions accessible by both RD and non-RD coding
  modes.

  Squashed-Change-Id : Iecb39dbf3d65436286ea3c7ffaa9920d0b3aff85

  Replace cpi->common with preset variable cm

  This commit replaces a few use cases of cpi->common with preset
  variable cm, to avoid unnecessary pointer fetch in the non-RD
  coding mode.

  Squashed-Change-Id : I4038f1c1a47373b8fd7bc5d69af61346103702f6

  [spatial svc]Implement lag in frames for spatial svc

  Squashed-Change-Id : I930dced169c9d53f8044d2754a04332138347409

  [spatial svc]Don’t skip motion search in first pass encoding

  Squashed-Change-Id : Ia6bcdaf5a5b80e68176f60d8d00e9b5cf3f9bfe3

  decode_test_driver : fix type size warning

  like vpx_codec_decode(), vpx_codec_peek_stream_info() takes an unsigned
  int, not size_t, parameter for buffer size

  Squashed-Change-Id : I4ce0e1fbbde461c2e1b8fcbaac3cd203ed707460

  decode_test_driver : check HasFailure() in RunLoop

  avoids unnecessary errors due to e.g., read (Next()) failures

  Squashed-Change-Id : I70b1d09766456f1c55367d98299b5abd7afff842

  Allow lossless breakout in non-rd mode decision.

  This is very helpful for large moving windows in screencasts.

  Squashed-Change-Id : I91b5f9acb133281ee85ccd8f843e6bae5cadefca

  Revert "Revert 3 patches from Hangyu to get Chrome to build :"

  This patch reverts the previous revert from Jim and also add a
  variable user_priv in the FrameWorker to save the user_priv
  passed from the application. In the decoder_get_frame function,
  the user_priv will be binded with the img. This change is needed
  or it will fail the unit test added here :
  https://gerrit.chromium.org/gerrit/#/c/70610/

  This reverts commit 9be46e4565f553460a1bbbf58d9f99067d3242ce.

  Squashed-Change-Id : I376d9a12ee196faffdf3c792b59e6137c56132c1

  test.mk : remove renamed file

  vp90-2-15-fuzz-flicker.webm was renamed in :
  c3db2d8 error check vp9 superframe parsing

  Squashed-Change-Id : I229dd6ca4c662802c457beea0f7b4128153a65dc

  vp9cx.mk : move avx c files outside of x86inc block

  same reasoning as :
  9f3a0db vp9_rtcd : correct avx2 references

  these are all intrinsics, so don’t depend on x86inc.asm

  Squashed-Change-Id : I915beaef318a28f64bfa5469e5efe90e4af5b827

  Dual arf : Name changes.

  Cosmetic patch only in response to comments on
  previous patches suggesting a couple of name changes
  for consistency and clarity.

  Squashed-Change-Id : Ida3a359b0d5755345660d304a7697a3a3686b2a3

  Make non-RD intra mode search txfm size dependent

  This commit fixes the potential issue in the non-RD mode decision
  flow that only checks part of the block to estimate the cost. It
  was due to the use of fixed transform size, in replacing the
  largest transform block size. This commit enables per transform
  block cost estimation of the intra prediction mode in the non-RD
  mode decision.

  Squashed-Change-Id : I14ff92065e193e3e731c2bbf7ec89db676f1e132

  Fix quality regression for multi arf off case.

  Bug introduced during multiple iterations on : I3831*

  gf_group->arf_update_idx[] cannot currently be used
  to select the arf buffer index if buffer flipping on overlays
  is enabled (still currently the case when multi arf OFF).

  Squashed-Change-Id : I4ce9ea08f1dd03ac3ad8b3e27375a91ee1d964dc

  Enable real-time version reference motion vector search

  This commit enables a fast reference motion vector search scheme.
  It checks the nearest top and left neighboring blocks to decide the
  most probable predicted motion vector. If it finds the two have
  the same motion vectors, it then skip finding exterior range for
  the second most probable motion vector, and correspondingly skips
  the check for NEARMV.

  The runtime of speed -5 goes down
  pedestrian at 1080p 29377 ms -> 27783 ms
  vidyo at 720p 11830 ms -> 10990 ms
  i.e., 6%-8% speed-up.

  For rtc set, the compression performance
  goes down by about -1.3% for both speed -5 and -6.

  Squashed-Change-Id : I2a7794fa99734f739f8b30519ad4dfd511ab91a5

  Add const mark to const values in non-RD coding mode

  Squashed-Change-Id : I65209fd1e06fc06833f6647cb028b414391a7017

  Change-Id : Ic0be67ac9ef48f64a8878a0b8f1b336f136bceac

• Managing Music Playback Channels

  30 juin 2013, par Multimedia Mike — General

  My Game Music Appreciation site allows users to interact with old video game music by toggling various channels, as long as the underlying synthesizer engine supports it.

  
  
  

  Users often find their way to the Nintendo DS section pretty quickly. This is when they notice an obnoxious quirk with the channel toggling feature : specifically, one channel doesn’t seem to map to a particular instrument or track.

  When it comes to computer music playback methodologies, I have long observed that there are 2 general strategies : Fixed channel and dynamic channel allocation.

  Fixed Channel Approach
  One of my primary sources of computer-based entertainment used to be watching music. Sure I listened to it as well. But for things like Amiga MOD files and related tracker formats, there was a rich ecosystem of fun music playback programs that visualized the music. There exist music visualization modes in various music players these days (such as iTunes and Windows Media Player), but those largely just show you a single wave form. These files were real time syntheses based on multiple audio channels and usually showed some form of analysis for each channel. My personal favorite was Cubic Player :

  
  
  

  Most of these players supported the concept of masking individual channels. In doing so, the user could isolate, study, and enjoy different components of the song. For many 4-channel Amiga MOD files, I observed that the common arrangement was to use the 4 channels for beat (percussion track), bass line, chords, and melody. Thus, it was easy to just listen to, e.g., the bass line in isolation.

  MODs and similar formats specified precisely which digital audio sample to play at what time and on which specific audio channel. To view the internals of one of these formats, one gets the impression that they contain an extremely computer-centric view of music.

  Dynamic Channel Allocation Algorithm
  MODs et al. enjoyed a lot of popularity, but the standard for computer music is MIDI. While MOD and friends took a computer-centric view of music, MIDI takes, well, a music-centric view of music.

  There are MIDI visualization programs as well. The one that came with my Gravis Ultrasound was called PLAYMIDI.EXE. It looked like this…

  
  
  

  … and it confused me. There are 16 distinct channels being visualized but some channels are shown playing multiple notes. When I dug into the technical details, I learned that MIDI just specifies what notes need to be played, at what times and frequencies and using which instrument samples, and it was the MIDI playback program’s job to make it happen.

  Thus, if a MIDI file specifies that track 1 should play a C major chord consisting of notes C, E, and G, it would transmit events “key-on C ; delta time 0 ; key-on E ; delta time 0 ; key-on G ; delta time … ; [other commands]“. If the playback program has access to multiple channels (say, up to 32, in the case of the GUS), the intuitive approach would be to maintain a pool of all available channels. Then, when it’s time to process the “key-on C” event, fetch the first available channel from the pool, mark it as in-use, play C on the channel, and return that channel to the pool when either the sample runs its course or the corresponding “key-off C” event is encountered in the MIDI command stream.

  About That Game Music
  Circling back around to my game music website, numerous supported systems use the fixed channel approach for playback while others use dynamic channel allocation approach, including evey Nintendo DS game I have so far analyzed.

  Which approach is better ? As in many technical matters, there are trade-offs either way. For many systems, the fixed channel approach is necessary because for many older audio synthesis systems, different channels had very specific purposes. The 8-bit NES had 5 channels : 2 square wave generators (used musically for melody/treble), 1 triangle wave generator (usually used for bass line), a noise generator (subverted for all manner of percussive sounds), and a limited digital channel (was sometimes assigned richer percussive sounds). Dynamic channel allocation wouldn’t work here.

  But the dynamic approach works great on hardware with 16 digital channels available like, for example, the Nintendo DS. Digital channels are very general-purpose. What about the SNES, with its 8 digital channels ? Either approach could work. In practice, most games used a fixed channel approach : Games might use 4-6 channels for music while reserving the remainder for various in-game sound effects. Some notable exceptions to this pattern were David Wise’s compositions for Rare’s SNES games (think Battletoads and the various Donkey Kong Country titles). These clearly use some dynamic channel approach since masking all but one channel will give you a variety of instrument sounds.

  Epilogue
  There ! That took a long time to explain but I find it fascinating for some reason. I need to distill it down to far fewer words because I want to make it a FAQ on my website for “Why can’t I isolate specific tracks for Nintendo DS games ?”

  Actually, perhaps I should remove the ability to toggle Nintendo DS channels in the first place. Here’s a funny tale of needless work : I found the Vio2sf engine for synthesizing Nintendo DS music and incorporated it into the program. It didn’t support toggling of individual channels so I figured out a way to add that feature to the engine. And then I noticed that most Nintendo DS games render that feature moot. After I released the webapp, I learned that I was out of date on the Vio2sf engine. The final insult was that the latest version already supports channel toggling. So I did the work for nothing. But then again, since I want to remove that feature from the UI, doubly so.