1. 21 Dec, 2010 4 commits
    • Timothy B. Terriberry's avatar
      Entropy coder clean-up. · 30df6cf3
      Timothy B. Terriberry authored
      This simplifies a good bit of the error handling, and should make it
       impossible to overrun the buffer in the encoder or decoder, while
       still allowing tell() to operate correctly after a bust.
      The encoder now tries to keep the range coder data intact after a
       bust instead of corrupting it with extra bits data, though this is
       not a guarantee (too many extra bits may have already been flushed).
      It also now correctly reports errors when the bust occurs merging the
       last byte of range coder and extra bits.
      
      A number of abstraction barrier violations were cleaned up, as well.
      This patch also includes a number of minor performance improvements:
       ec_{enc|dec}_bits() in particular should be much faster.
      
      Finally, tf_select was changed to be coded with the range coder
       rather than extra bits, so that it is at the front of the packet
       (for unequal error protection robustness).
      30df6cf3
    • Jean-Marc Valin's avatar
      Added highest allocation line possible · 59858633
      Jean-Marc Valin authored
      59858633
    • Jean-Marc Valin's avatar
      Ordering Hadamard frequencies when increasing the time-resolution. · dc6d69e6
      Jean-Marc Valin authored
      This means we're "time-ordered" in all cases except when increasing
      the time resolution on frames that already use short blocks.
      There's no reordering when increasing the frequency resolution
      on short blocks.
      dc6d69e6
    • Jean-Marc Valin's avatar
      Tuning the dynamic allocation probability and increment · 034efa52
      Jean-Marc Valin authored
      Dynalloc becomes 2x more likely every time we use it, until it
      reaches a probability of 1/4. Allocation increments now have
      a floor of 1/8 bit/sample and a ceiling of 1 bit/sample.
      034efa52
  2. 20 Dec, 2010 4 commits
  3. 19 Dec, 2010 2 commits
  4. 18 Dec, 2010 3 commits
    • Timothy B. Terriberry's avatar
      More simplifications to the decoder renormalization loop. · 53454f49
      Timothy B. Terriberry authored
      This removes an XOR, an ADD, and an AND, and replaces them with
       an AND NOT in ec_dec_normalize().
      Also, simplify the loop structure of ec_dec_cdf() and eliminate a
       CMOV.
      53454f49
    • Timothy B. Terriberry's avatar
      Replace ec_{enc|dec}_bit_prob() with ec_{enc|dec}_bit_logp(). · e86fb268
      Timothy B. Terriberry authored
      All of our usage of ec_{enc|dec}_bit_prob had the probability of a
       "one" being a power of two.
      This adds a new ec_{enc|dec}_bit_logp() function that takes this
       explicitly into account.
      It introduces less rounding error than the bit_prob version, does not
       require 17-bit integers to be emulated by ec_{encode|decode}_bin(),
       and does not require any multiplies or divisions at all.
      It is exactly equivalent to
       ec_encode_bin(enc,_val?0:(1<<_logp)-1,(1<<_logp)-(_val?1:0),1<<_logp)
      
      The old ec_{enc|dec}_bit_prob functions are left in place for now,
       because I am not sure if SILK is still using them or not when
       combined in Opus.
      e86fb268
    • Timothy B. Terriberry's avatar
      Subtract one from dif in the range decoder. · 8c23a3a0
      Timothy B. Terriberry authored
      It turns out to be more convenient to store dif=low+rng-code-1
       instead of dif=low+rng-code.
      This gets rid of a decrement in the normal decode path, replaces a
       decrement and an "and" in the normalization loop with a single
       add, and makes it clear that the new ec_dec_cdf() will not result
       in an infinite loop.
      This does not change the bitstream.
      8c23a3a0
  5. 17 Dec, 2010 7 commits
    • Timothy B. Terriberry's avatar
      Add a generic CDF decoding routine. · a0b664df
      Timothy B. Terriberry authored
      This decodes a value encoded with ec_encode_bin() without using any
       divisions.
      It is only meant for small alphabets.
      If a symbol can take on a large number of possible values, a binary
       search would be better.
      
      This patch also converts spread_decision to use it, since it is
       faster and introduces less rounding error to encode a single
       decision for the entire value than to encode it a bit at a time.
      a0b664df
    • Jean-Marc Valin's avatar
      Giving less bits to single-bin bands. · 3fed34ae
      Jean-Marc Valin authored
      This improves the allocation for 2.5 ms frames.
      3fed34ae
    • Jean-Marc Valin's avatar
      Fixed the spreading probabilities (1-x) · f33a7fb8
      Jean-Marc Valin authored
      f33a7fb8
    • Timothy B. Terriberry's avatar
      Re-organize spreading/folding constants. · 320cf2e2
      Timothy B. Terriberry authored
      These were stored internally in one order and in the bitstream in a
       different order.
      Both used bare constants, making it unclear what either actually
       meant.
      This changes them to use the same order, gives them named constants,
       and renames all the "fold" decision stuff to "spread" instead,
       since that is what it is really controlling.
      320cf2e2
    • Jean-Marc Valin's avatar
      Re-enabling post-filter on 2.5 ms frames · cd84e3d0
      Jean-Marc Valin authored
      Also, now forcing MS stereo for 2.5 frames because the current
      analysis isn't reliable.
      cd84e3d0
    • Timothy B. Terriberry's avatar
      More cleanups to compute_allocation(). · 428a77d6
      Timothy B. Terriberry authored
      The bisection search in compute_allocation() was not using the same
       method to count psum as interp_bits2pulses, i.e., it did not
       include the 64*C<<BITRES<<LM allocation ceiling (this adds at most
       84 max operations/frame, and so should have a trivial CPU cost).
      Again, I wouldn't want to try to explain why these are different in
       a spec, so let's make them the same.
      
      In addition, the procedure used to fill in bits1 and bits2 after the
       bisection search was not the same as the one used during the
       bisection search.
      I.e., the
            if (bits1[j] > 0)
                     bits1[j] += trim_offset[j];
       step was not also done for bits2, so bits1[j] + bits2[j] would not
       be equal to what was computed earlier for the hi line, and would
       not be guaranteed to be larger than total.
      We now compute both allocation lines in the same manner, and then
       obtain bits2 by subtracting them, instead of trying to compute the
       offset from bits1 up front.
      
      Finally, there was nothing to stop a bitstream from boosting a band
       beyond the number of bits remaining, which means that bits1 would
       not produce an allocation less than or equal to total, which means
       that some bands would receive a negative allocation in the decoder
       when the "left over" negative bits were redistributed to other
       bands.
      This patch only adds the dynalloc offset to allocation lines greater
       than 0, so that an all-zeros floor still exists; the effect is that
       a dynalloc boost gets linearly scaled between allocation lines 0 and
       1, and is constant (like it was before) after that.
      We don't have to add the extra condition to the bisection search,
       because it never examines allocation line 0.
      This re-writes the indexing in the search to make that explicit;
       it was tested and gives exactly the same results in exactly the
       same number of iterations as the old search.
      428a77d6
    • Timothy B. Terriberry's avatar
      Give the bit we reserved to end skipping back when we don't use it. · 76ea41e1
      Timothy B. Terriberry authored
      Commit 8e447678 increased the number of cases where we end skipping
       without explicit signaling.
      Before, this would cause the bit we reserved for this purpose to
       either a) get grabbed by some N=1 band to code its sign bits or
       b) wind up as part of the fine energy at the end.
      This patch gives it back to the band where we stopped skipping,
       which is either the first band, or a band that was boosted by
       dynalloc.
      This allows the bit to be used for shape coding in that band, and
       allows the better computation of the fine offset, since the band
       knows it will get that bit in advance.
      
      With this change, we now guarantee that the number of bits allocated
       by compute_allocation() is exactly equal to the input total, less
       the bits consumed by skip flags during allocation itself (assuming
       total was non-negative; for negative total, no bits are emitted,
       and no bits are allocated).
      76ea41e1
  6. 16 Dec, 2010 7 commits
    • Jean-Marc Valin's avatar
    • Gregory Maxwell's avatar
      Terminate the coding of skip bits at the last dynalloc boosted band. Otherwise... · 8e447678
      Gregory Maxwell authored
      Terminate the coding of skip bits at the last dynalloc boosted band. Otherwise the bitstream allows non-sensible behavior by the encoder (dynallocing bits into a band and then skipping it). This reduces skip bit overhead by about 2-3% at moderate bitrates with the current encoder.
      8e447678
    • Jean-Marc Valin's avatar
    • Jean-Marc Valin's avatar
      Comments, low bit-rate busting avoidance · 5c80391b
      Jean-Marc Valin authored
      5c80391b
    • Jean-Marc Valin's avatar
      Setting fine_priority for skipped bands · df6620eb
      Jean-Marc Valin authored
      df6620eb
    • Timothy B. Terriberry's avatar
      Rebalance N=1 allocations during interp_bits2pulses(). · 66c5ab4f
      Timothy B. Terriberry authored
      Excess fractions of a bit can't be re-used in N=1 bands during
       quant_all_bands() because there's no shape, only a sign bit.
      This meant that all the fractional bits in these bands accumulated,
       often up to 5 or 6 bits for stereo, until the first band with N>1,
       where they were dumped all at once.
      This patch moves the rebalancing for N=1 bands to
       interp_bits2pulses() instead, where excess bits still have a
       chance to be moved into fine energy.
      66c5ab4f
    • Timothy B. Terriberry's avatar
      Change strategies for allocation hole prevention. · 405e6a99
      Timothy B. Terriberry authored
      In commit ffe10574 JM added a "done" flag to the allocation
       interpolation loop: whenver a band did not have enough bits to
       pass its threshold for receiving PVQ pulses, all of the rest of
       band were given just enough bits for fine energy only.
      This patch implements JM's "backwards done" idea: instead work
       backwards, dropping bands until the first band that is over the
       threshold is encountered, and don't artificially reduce the
       allocation any more after that.
      This is much more stable: we can continue to signal manual skips if
       we want to, but we aren't forced to skip a large number of bands
       because of an isolated hole in he allocation.
      
      This makes low-bitrate 120-sample frames much less rough.
      It also reduces the force skip threshold from
       alloc_floor+(1<<BITRES)+1 to just alloc_floor+(1<<BITRES), because
       the former can now cascade to cause many bands to be skipped.
      The difference here is subtle, and increases signaling overhead by
       0.11% of the total bitrate, but Monty confirmed that removing the
       +1 reduces noise in the bass (i.e., in N=1 bands where such a skip
       could cascade).
      
      Finally the 64*C<<BITRES<<LM ceiling is moved into the bisection
       search, instead of just being imposed afterwards, again because I
       wouldn't want to try to explain in a spec why they're different.
      405e6a99
  7. 15 Dec, 2010 6 commits
    • Timothy B. Terriberry's avatar
      More compute_allocation() fixes. · 7627b9f6
      Timothy B. Terriberry authored
      1) Continue to update left and percoeff if we skip all the way to the
          first band.
         This doesn't actually matter for correctness, but I don't want to
          try to explain in a spec why we aren't doing this.
      2) Force all the bits in skipped bands to go to fine energy.
         Before some of them could continue to be given to pulses, even though no
          pulses would actually be allocate for them.
      7627b9f6
    • Timothy B. Terriberry's avatar
      Store the total budget of compute_allocation in BITRES units. · 4777f069
      Timothy B. Terriberry authored
      The margin of safety was supposed to be 1/8th bit, not 1 bit, and the
       bit we reserved to terminate skip signalling before was actually 8
       bits.
      This patch updates the margin of safety to the correct value and
       accounts for the one bit (not 8) needed for skip signalling.
      It also fixes the remainder calculation in the skip loop to work
       correctly when start>0.
      4777f069
    • Timothy B. Terriberry's avatar
      Don't stop force-skipping on the first manually skipped band. · 283a9b60
      Timothy B. Terriberry authored
      Now that manual skipping is in the same loop as forced skipping, there
       is no reason to do all of one, then all of the other.
      This ensures we won't propagate bits to bands that have almost nothing
       later in quant_all_bands() because we didn't have enough bits to
       signal them skipped.
      283a9b60
    • Timothy B. Terriberry's avatar
      Move skip coding into interp_bits2pulses(). · b2f59009
      Timothy B. Terriberry authored
      This allows us to a) not pay a coding cost to avoid skipping bands that are
       stupid to skip (e.g., the first band, or bands that have so few bits that we
       wouldn't redistribute anything) and b) not reserve bits to pay that cost.
      b2f59009
    • Timothy B. Terriberry's avatar
      More allocation function updates. · 7cbf168c
      Timothy B. Terriberry authored
      This moves more of the decisions about when to stop skipping bands into the
       encoder-specific branch, so they are not forced in the decoder (because there
       is currently no bit-savings from forcing them).
      It also no longer requires an extra bit to code the fine energy in a skipped
       band: that was meant to account for the skip flag, but we already subtracted
       that.
      7cbf168c
    • Jean-Marc Valin's avatar
      Tim just rewrote half of the bit allocator -- hope it works now · ffe10574
      Jean-Marc Valin authored
      Making sure we never waste bits due to band skip and also making
      sure we don't skip bands "in the middle".
      ffe10574
  8. 14 Dec, 2010 4 commits
  9. 13 Dec, 2010 2 commits
  10. 10 Dec, 2010 1 commit