Differences

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--- doc:appunti:linux:video:ffmpeg_final_rendering [2023/11/13 12:38] – [Encoding for High Definition Video] niccolo
+++ doc:appunti:linux:video:ffmpeg_final_rendering [2024/07/31 09:57] (current) – [Two pass encoding] 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 16: / Line 15: @@
 ^ Basic x264        | Preset: **slow** (or less), Tuning: **film**, Profile: **High**, IDC Level: **Auto** |
 ^ Video encoding    | Average Bitrate (Two Pass), Average Bitrate 4096 kb/s (about 1.8 Gb per hour)  |
-^ Pixel format      | Our source videos use **yuvj420p pixel format**, so we use the same for the final rendering.  |
+^ Pixel format      | Our source videos use **yuvj420p pixel format**, so we use the same for the final rendering (see the considerations below).  |
 ^ Bits per sample   | Our source videos use **8 bits per raw sample**, so we stay on this.  |
-^ Color range       | We use the **full range** color. The **j** letter in the //yuvj420p// pixel format means that YUV values are stored as full 0-255 range (**8 bit**), as in JPEG. This is better than the so called //studio swing//, with Y in the 16-235 range and UV in the 16-240 range.  |
+^ Color range       | We use the **full range** of colors. The **j** letter in the //yuvj420p// pixel format means that YUV values are stored as full 0-255 range (8 bits), as in JPEG. This is better than the so called //studio swing//, with Y in the 16-235 range and UV in the 16-240 range.  |
 ^ Audio codec       | <del>Lame MP3</del> Vorbis  |
 ^ Audio bitrate     | CBR 192 (or higher)  |
@@ Line 36: / Line 35: @@
     -filter:v "scale=1366x768" -aspect "16:9" \
     -vcodec 'libx264' -pix_fmt 'yuvj420p' -preset 'veryslow' -tune 'film' -profile:v 'high' -level:v 5 \
+    -b:v 4M -maxrate:v 6M -bufsize:v 6M \
     -acodec copy \
     "2022-05_balcani.mkv"
 </code>
+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 =====