diff options
Diffstat (limited to 'libavcodec/dv.c')
-rw-r--r-- | libavcodec/dv.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/libavcodec/dv.c b/libavcodec/dv.c index 9c31570..d4661fe 100644 --- a/libavcodec/dv.c +++ b/libavcodec/dv.c @@ -658,8 +658,22 @@ static always_inline void dv_set_class_number(DCTELEM* blk, EncBlockInfo* bi, const uint8_t* zigzag_scan, const int *weight, int bias) { int i, area; + /* We offer two different methods for class number assignment: the + method suggested in SMPTE 314M Table 22, and an improved + method. The SMPTE method is very conservative; it assigns class + 3 (i.e. severe quantization) to any block where the largest AC + component is greater than 36. ffmpeg's DV encoder tracks AC bit + consumption precisely, so there is no need to bias most blocks + towards strongly lossy compression. Instead, we assign class 2 + to most blocks, and use class 3 only when strictly necessary + (for blocks whose largest AC component exceeds 255). */ + +#if 0 /* SMPTE spec method */ static const int classes[] = {12, 24, 36, 0xffff}; - int max=12; +#else /* improved ffmpeg method */ + static const int classes[] = {-1, -1, 255, 0xffff}; +#endif + int max=classes[0]; int prev=0; bi->mb[0] = blk[0]; |