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content-based keyframe detection

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This commit is contained in:
minjaesong
2025-08-25 17:34:56 +09:00
parent 0e5a778fe5
commit 7670ef1b35
1 changed files with 67 additions and 3 deletions
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70
video_encoder/encoder_tev.c
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@@ -659,6 +659,7 @@ static void encode_block(tev_encoder_t *enc, int block_x, int block_y, int is_ke
// Calculate SAD for skip mode (no motion compensation)
int skip_sad = 0;
int skip_color_diff = 0;
for (int dy = 0; dy < 16; dy++) {
for (int dx = 0; dx < 16; dx++) {
int x = start_x + dx;
@@ -675,6 +676,16 @@ static void encode_block(tev_encoder_t *enc, int block_x, int block_y, int is_ke
enc->previous_rgb[cur_offset + 2]) / 4;
skip_sad += abs(cur_luma - prev_luma);
// Also check for color differences to prevent SKIP on color changes
int cur_r = enc->current_rgb[cur_offset];
int cur_g = enc->current_rgb[cur_offset + 1];
int cur_b = enc->current_rgb[cur_offset + 2];
int prev_r = enc->previous_rgb[cur_offset];
int prev_g = enc->previous_rgb[cur_offset + 1];
int prev_b = enc->previous_rgb[cur_offset + 2];
skip_color_diff += abs(cur_r - prev_r) + abs(cur_g - prev_g) + abs(cur_b - prev_b);
}
}
}
@@ -717,7 +728,8 @@ static void encode_block(tev_encoder_t *enc, int block_x, int block_y, int is_ke
}
// Mode decision with strict thresholds for quality
if (skip_sad <= 64) {
// Require both low luma difference AND low color difference for SKIP
if (skip_sad <= 64 && skip_color_diff <= 192) {
// Very small difference - skip block (copy from previous frame)
block->mode = TEV_MODE_SKIP;
block->mv_x = 0;
@@ -930,9 +942,61 @@ static int write_tev_header(FILE *output, tev_encoder_t *enc) {
return 0;
}
// Detect scene changes by analyzing frame differences
static int detect_scene_change(tev_encoder_t *enc) {
if (!enc->previous_rgb || !enc->current_rgb) {
return 0; // No previous frame to compare
}
long long total_diff = 0;
int changed_pixels = 0;
// Sample every 4th pixel for performance (still gives good detection)
for (int y = 0; y < enc->height; y += 2) {
for (int x = 0; x < enc->width; x += 2) {
int offset = (y * enc->width + x) * 3;
// Calculate color difference
int r_diff = abs(enc->current_rgb[offset] - enc->previous_rgb[offset]);
int g_diff = abs(enc->current_rgb[offset + 1] - enc->previous_rgb[offset + 1]);
int b_diff = abs(enc->current_rgb[offset + 2] - enc->previous_rgb[offset + 2]);
int pixel_diff = r_diff + g_diff + b_diff;
total_diff += pixel_diff;
// Count significantly changed pixels (threshold of 30 per channel average)
if (pixel_diff > 90) {
changed_pixels++;
}
}
}
// Calculate metrics for scene change detection
int sampled_pixels = (enc->height / 2) * (enc->width / 2);
double avg_diff = (double)total_diff / sampled_pixels;
double changed_ratio = (double)changed_pixels / sampled_pixels;
// Scene change thresholds:
// - High average difference (> 40) OR
// - Large percentage of changed pixels (> 30%)
return (avg_diff > 40.0) || (changed_ratio > 0.30);
}
// Encode and write a frame
static int encode_frame(tev_encoder_t *enc, FILE *output, int frame_num) {
int is_keyframe = (frame_num % KEYFRAME_INTERVAL) == 0;
// Check for scene change or time-based keyframe
int is_scene_change = detect_scene_change(enc);
int is_time_keyframe = (frame_num % KEYFRAME_INTERVAL) == 0;
int is_keyframe = is_time_keyframe || is_scene_change;
// Verbose output for keyframe decisions
if (enc->verbose && is_keyframe) {
if (is_scene_change && !is_time_keyframe) {
printf("Frame %d: Scene change detected, inserting keyframe\n", frame_num);
} else if (is_time_keyframe) {
printf("Frame %d: Time-based keyframe (interval: %d)\n", frame_num, KEYFRAME_INTERVAL);
}
}
int blocks_x = (enc->width + 15) / 16;
int blocks_y = (enc->height + 15) / 16;
@@ -1131,7 +1195,7 @@ static int start_video_conversion(tev_encoder_t *enc) {
// Frame rate conversion requested
snprintf(command, sizeof(command),
"ffmpeg -v quiet -i \"%s\" -f rawvideo -pix_fmt rgb24 "
"-vf \"scale=%d:%d:force_original_aspect_ratio=increase,crop=%d:%d,fps=%d\" "
"-vf \"fps=%d,scale=%d:%d:force_original_aspect_ratio=increase,crop=%d:%d\" "
"-y - 2>&1",
enc->input_file, enc->width, enc->height, enc->width, enc->height, enc->output_fps);
} else {