chore: reduce keyframe interval in MPEG-DASH H.264 presets

* There is no perceivable difference between a keyframe interval of 1
  and 2 in terms of playback, but the file size is significantly smaller
  with a keyframe interval of 2 (as one would expect).

Author: bajankristof

lib/ffmpeg/presets/dash/h264.rb

@@ -18,7 +18,7 @@ def h264_360p(
           metadata: nil,
           threads: FFMPEG.threads,
           segment_duration: 4,
-          keyframe_interval: 1,
+          keyframe_interval: 2,
           audio_bit_rate: '128k',
           frame_rate: 30,
           ld_frame_rate: 24,
@@ -48,7 +48,7 @@ def h264_480p(
           metadata: nil,
           threads: FFMPEG.threads,
           segment_duration: 4,
-          keyframe_interval: 1,
+          keyframe_interval: 2,
           audio_bit_rate: '128k',
           frame_rate: 30,
           ld_frame_rate: 24,
@@ -79,7 +79,7 @@ def h264_720p(
           metadata: nil,
           threads: FFMPEG.threads,
           segment_duration: 4,
-          keyframe_interval: 1,
+          keyframe_interval: 2,
           audio_bit_rate: '128k',
           ld_frame_rate: 24,
           sd_frame_rate: 30,
@@ -112,7 +112,7 @@ def h264_1080p(
           metadata: nil,
           threads: FFMPEG.threads,
           segment_duration: 4,
-          keyframe_interval: 1,
+          keyframe_interval: 2,
           audio_bit_rate: '128k',
           ld_frame_rate: 24,
           sd_frame_rate: 30,
@@ -146,7 +146,7 @@ def h264_1440p(
           metadata: nil,
           threads: FFMPEG.threads,
           segment_duration: 4,
-          keyframe_interval: 1,
+          keyframe_interval: 2,
           audio_bit_rate: '128k',
           ld_frame_rate: 24,
           sd_frame_rate: 30,
@@ -181,7 +181,7 @@ def h264_4k(
           metadata: nil,
           threads: FFMPEG.threads,
           segment_duration: 4,
-          keyframe_interval: 1,
+          keyframe_interval: 2,
           audio_bit_rate: '128k',
           ld_frame_rate: 24,
           sd_frame_rate: 30,
@@ -231,7 +231,7 @@ def initialize(
           metadata: nil,
           threads: FFMPEG.threads,
           segment_duration: 4,
-          keyframe_interval: 1,
+          keyframe_interval: 2,
           h264_presets: [Presets.h264_1080p, Presets.h264_720p, Presets.h264_480p, Presets.h264_360p],
           ld_h264_presets: [Presets.h264_240p, Presets.h264_144p],
           &