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--- doc:appunti:linux:video:ffmpeg_final_rendering [2024/07/29 11:52] – [Encoding for High Definition Video] niccolo
+++ doc:appunti:linux:video:ffmpeg_final_rendering [2026/08/23 21:03] (current) – [Pixel format considerations] niccolo
@@ Line 1: / Line 1: @@
-====== Final Rendering in x264 with ffmpeg ======
+====== Final Rendering with libx264 and ffmpeg ======
 Whether you are working with **Ffmepg**, **Avidemux** or **Olive Video Editor**, you should be wondering what parameters to use to final render a video montage. Here are my choices for some specific purpose.
 ===== Encoding for High Definition Video =====
@@ Line 42: / Line 41: @@
 Notice that we selected a target bitrate of **4 Mbps** and a maximum bitrate of **6 Mbps**. Sepcifying both the //bitrate// and the //max bitrate tolerance// requires also to specify a //buffer size//; ''ffmpeg'' will re-adjust the bitrate on each buffer size, so if the buffer size is equal to the max rate, ffmpeg will re-calculate the bitrate at least every second.
+=====  A warning about the H.264 profile level =====
+It turned out that **Kodi 19.4** (running on a Raspberry Pi 4 with **Raspbian GNU/Linux 11 Bullseye** o.s.) has some problems playing H.264 video files depending on the video format profile used for the encoding. The video actually starts to play, but nothing is seen on the screen; sometimes the screen goes totally green. Similarly a **Google TV** with Kodi 21.0 has problems with the same files, showing stuttering and video artifacts.
+Here it is a table of playing capabilities based on experimental testing:
+^ Format profile  ^ Resolution   ^ Mbps  ^ Can play on Kodi  ^
+| High@L5         | 1366x768     |    4 | yes  |
+| High@L4         | 1920x1080    |    6 | Yes  |
+| High@L4.1       | 1920x1080    |    6 | Yes  |
+| High@5          | 1920x1080    |    4 | No   |
+| High@5          | 1920x1080    |    6 | No   |
+=====  Two pass encoding =====
+Here it is a recipe of **two-pass encoding** from an high quality //master// produced with [[olive_editor_tools#export_media|Olive Video Editor]]. The target video will be a **6 Mbit** stream, **1920x1080@30**. The profile level selected is **High@L4.1**, so that the video will play nicely with Kodi 19.4 on the Raspberry Pi 4:
+<code bash>
+TITLE='Marocco - Maggio 2024'
+ffmpeg \
+    -i full32bit-veryslow-crf18-fullcolor.mkv \
+    -metadata title="$TITLE" -metadata:s:v:0 title="$TITLE" \
+    -vcodec 'libx264' -pix_fmt 'yuvj420p' -preset 'veryslow' -tune 'film' \
+    -profile:v 'high' -level:v 4.1 \
+    -b:v 6M -maxrate:v 9M -bufsize:v 18M \
+    -x264-params 'keyint=64' \
+    -an \
+    -pass 1 \
+    -f matroska -y /dev/null
+# First pass produces two files: ffmpeg2pass-0.log and ffmpeg2pass-0.log.mbtree.
+ffmpeg \
+    -i full32bit-veryslow-crf18-fullcolor.mkv \
+    -metadata title="$TITLE" -metadata:s:v:0 title="$TITLE" \
+    -vcodec 'libx264' -pix_fmt 'yuvj420p' -preset 'veryslow' -tune 'film' \
+    -profile:v 'high' -level:v 4.1 \
+    -b:v 6M -maxrate:v 9M -bufsize:v 18M \
+    -x264-params 'keyint=64' \
+    -an \
+    -pass 2 \
+    -f matroska marocco-twopass-6max9-level41.mkv
+</code>
+The transcoding works on the video only, suppressing any audio stream (**%%-an%%** option). Using the **keyint=64** option will produce a keyframe every 64 frames (about two seconds), this make seeking back and forward in the video more smooth.
 =====  Pixel format considerations =====
@@ Line 51: / Line 94: @@
 {{subsampling.png?400|Chroma Subsampling}}
-Is file size is not a concern, we might ask ourselves whether a pixel format with less loss of chroma information would be preferable. Obviously is useless to add more chroma information if the final rendering has the same resolution of the original video, but if we are **scaling down** the video resolution we may **retain chroma information** using a different pixel format.
+If file size is not a concern, we might ask ourselves whether a pixel format with less loss of chroma information would be preferable. Obviously is useless to add more chroma information if the final rendering has the same resolution of the original video, but if we are **scaling down** the video resolution we may **retain chroma information** using a different pixel format.
 The fact is that **in movies 4:2:0 is almost lossless visually**, which is why it can be found used in Blu-ray discs and a lot of modern video cameras. There is virtually no advantage to using 4:4:4 for consuming video content.