The comments supposed to track the possible value of the qmat and qmat16 matrices, but they were not updated properly in the long history of the mpegvideo encoder. Also they wrongly assumed the usage of built-in quantizer matrices and linear quantization.
Signed-off-by: Marton Balint <[email protected]> --- libavcodec/mpegvideo_enc.c | 37 ++++++++++++++++++++----------------- 1 file changed, 20 insertions(+), 17 deletions(-) diff --git a/libavcodec/mpegvideo_enc.c b/libavcodec/mpegvideo_enc.c index c5f20c2d85..7001d5a566 100644 --- a/libavcodec/mpegvideo_enc.c +++ b/libavcodec/mpegvideo_enc.c @@ -133,11 +133,11 @@ void ff_convert_matrix(MpegEncContext *s, int (*qmat)[64], for (i = 0; i < 64; i++) { const int j = s->idsp.idct_permutation[i]; int64_t den = (int64_t) qscale2 * quant_matrix[j]; - /* 16 <= qscale * quant_matrix[i] <= 7905 - * Assume x = ff_aanscales[i] * qscale * quant_matrix[i] - * 19952 <= x <= 249205026 - * (1 << 36) / 19952 >= (1 << 36) / (x) >= (1 << 36) / 249205026 - * 3444240 >= (1 << 36) / (x) >= 275 */ + /* 1 * 1 <= qscale2 * quant_matrix[j] <= 112 * 255 + * Assume x = qscale2 * quant_matrix[j] + * 1 <= x <= 28560 + * (1 << 22) / 1 >= (1 << 22) / (x) >= (1 << 22) / 28560 + * 4194304 >= (1 << 22) / (x) >= 146 */ qmat[qscale][i] = (int)((UINT64_C(2) << QMAT_SHIFT) / den); } @@ -145,11 +145,11 @@ void ff_convert_matrix(MpegEncContext *s, int (*qmat)[64], for (i = 0; i < 64; i++) { const int j = s->idsp.idct_permutation[i]; int64_t den = ff_aanscales[i] * (int64_t) qscale2 * quant_matrix[j]; - /* 16 <= qscale * quant_matrix[i] <= 7905 - * Assume x = ff_aanscales[i] * qscale * quant_matrix[i] - * 19952 <= x <= 249205026 - * (1 << 36) / 19952 >= (1 << 36) / (x) >= (1 << 36) / 249205026 - * 3444240 >= (1 << 36) / (x) >= 275 */ + /* 1247 * 1 * 1 <= ff_aanscales[i] * qscale2 * quant_matrix[j] <= 31521 * 112 * 255 + * Assume x = ff_aanscales[i] * qscale2 * quant_matrix[j] + * 1247 <= x <= 900239760 + * (1 << 36) / 1247 >= (1 << 36) / (x) >= (1 << 36) / 900239760 + * 55107840 >= (1 << 36) / (x) >= 76 */ qmat[qscale][i] = (int)((UINT64_C(2) << (QMAT_SHIFT + 14)) / den); } @@ -157,14 +157,17 @@ void ff_convert_matrix(MpegEncContext *s, int (*qmat)[64], for (i = 0; i < 64; i++) { const int j = s->idsp.idct_permutation[i]; int64_t den = (int64_t) qscale2 * quant_matrix[j]; - /* We can safely suppose that 16 <= quant_matrix[i] <= 255 - * Assume x = qscale * quant_matrix[i] - * So 16 <= x <= 7905 - * so (1 << 19) / 16 >= (1 << 19) / (x) >= (1 << 19) / 7905 - * so 32768 >= (1 << 19) / (x) >= 67 */ + /* 1 * 1 <= qscale2 * quant_matrix[j] <= 112 * 255 + * Assume x = qscale2 * quant_matrix[j] + * 1 <= x <= 28560 + * (1 << 22) / 1 >= (1 << 22) / (x) >= (1 << 22) / 28560 + * 4194304 >= (1 << 22) / (x) >= 146 + * + * 1 <= x <= 28560 + * (1 << 17) / 1 >= (1 << 17) / (x) >= (1 << 17) / 28560 + * 131072 >= (1 << 17) / (x) >= 4 */ + qmat[qscale][i] = (int)((UINT64_C(2) << QMAT_SHIFT) / den); - //qmat [qscale][i] = (1 << QMAT_SHIFT_MMX) / - // (qscale * quant_matrix[i]); qmat16[qscale][0][i] = (2 << QMAT_SHIFT_MMX) / den; if (qmat16[qscale][0][i] == 0 || -- 2.43.0 _______________________________________________ ffmpeg-devel mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
