avfilter/vf_interlace: restore lowpass mode constants

The documentation still mentions numerical constants in addition to textual
ones. It is also wrong to use distinct modes as flags and it disallows us to
actually use the flags field for real flags in the future.
Signed-off-by: Marton Balint <cus@passwd.hu>

libavfilter/tinterlace.h

@@ -37,6 +37,12 @@
 #define TINTERLACE_FLAG_CVLPF 2
 #define TINTERLACE_FLAG_EXACT_TB 4
 
+enum VLPFilter {
+    VLPF_OFF = 0,
+    VLPF_LIN = 1,
+    VLPF_CMP = 2,
+};
+
 enum TInterlaceMode {
     MODE_MERGE = 0,
     MODE_DROP_EVEN,
@@ -59,6 +65,7 @@ typedef struct TInterlaceContext {
     int mode;                   ///< TInterlaceMode, interlace mode selected
     AVRational preout_time_base;
     int flags;                  ///< flags affecting interlacing algorithm
+    int lowpass;                ///< legacy interlace filter lowpass mode
     int frame;                  ///< number of the output frame
     int vsub;                   ///< chroma vertical subsampling
     AVFrame *cur;

libavfilter/vf_tinterlace.c

@@ -63,10 +63,10 @@ static const AVOption interlace_options[] = {
    { "scan",              "scanning mode", OFFSET(mode), AV_OPT_TYPE_INT, {.i64 = MODE_TFF}, 0, 1, FLAGS, "mode"},
    { "tff",               "top field first",                              0, AV_OPT_TYPE_CONST, {.i64 = MODE_TFF}, INT_MIN, INT_MAX, FLAGS, .unit = "mode"},
    { "bff",               "bottom field first",                           0, AV_OPT_TYPE_CONST, {.i64 = MODE_BFF}, INT_MIN, INT_MAX, FLAGS, .unit = "mode"},
-   { "lowpass",           "set vertical low-pass filter", OFFSET(flags), AV_OPT_TYPE_FLAGS,   {.i64 = TINTERLACE_FLAG_VLPF}, 0, 2, FLAGS, "flags" },
-   { "off",               "disable vertical low-pass filter",             0, AV_OPT_TYPE_CONST, {.i64 = 0}, INT_MIN, INT_MAX, FLAGS, "flags" },
-   { "linear",            "linear vertical low-pass filter",              0, AV_OPT_TYPE_CONST, {.i64 = TINTERLACE_FLAG_VLPF}, INT_MIN, INT_MAX, FLAGS, "flags" },
-   { "complex",           "complex vertical low-pass filter",             0, AV_OPT_TYPE_CONST, {.i64 = TINTERLACE_FLAG_CVLPF},INT_MIN, INT_MAX, FLAGS, "flags" },
+   { "lowpass",           "set vertical low-pass filter", OFFSET(lowpass), AV_OPT_TYPE_INT,   {.i64 = VLPF_LIN}, 0, 2, FLAGS, "lowpass" },
+   {     "off",           "disable vertical low-pass filter",             0, AV_OPT_TYPE_CONST, {.i64 = VLPF_OFF}, INT_MIN, INT_MAX, FLAGS, "lowpass" },
+   {     "linear",        "linear vertical low-pass filter",              0, AV_OPT_TYPE_CONST, {.i64 = VLPF_LIN}, INT_MIN, INT_MAX, FLAGS, "lowpass" },
+   {     "complex",       "complex vertical low-pass filter",             0, AV_OPT_TYPE_CONST, {.i64 = VLPF_CMP}, INT_MIN, INT_MAX, FLAGS, "lowpass" },
 
    { NULL }
 };
@@ -518,6 +518,11 @@ static int init_interlace(AVFilterContext *ctx)
     if (tinterlace->mode <= MODE_BFF)
         tinterlace->mode += MODE_INTERLEAVE_TOP;
 
+    if (tinterlace->lowpass == VLPF_LIN)
+        tinterlace->flags |= TINTERLACE_FLAG_VLPF;
+    if (tinterlace->lowpass == VLPF_CMP)
+        tinterlace->flags |= TINTERLACE_FLAG_CVLPF;
+
     return 0;
 }