Differences

This shows you the differences between two versions of the page.

--- doc:appunti:linux:video:ffmpeg [2020/12/07 17:26] – [Deinterlace] niccolo
+++ doc:appunti:linux:video:ffmpeg [2023/11/13 11:24] (current) – [Doppiaggio audio con Ardour] niccolo
@@ Line 264: / Line 264: @@
 </code>
-====== Final rendering (re-encoding) ======
-The video stream recorded by the Xiaomi Yi camera is **1920x1080 pixels** at a variable bitrate of **12.0 Mb/s**. Because we watch it on a simple TV set capable only of 1366x768 pixels, we we re-encode it with the following settings:
+====== Re-encoding with tonal correction ======
-^ Video codec     | MPEG-4 AVC (x264)  |
+We had some video clips recorded with an **SJCAM Sj8 Pro** camera with a **bad color balance and saturation** due some bad tables [[..:..:hardware:sjcam-8pro-custom-firmware|loaded into the firmware]]. It is possibile to re-encode all the video clips applying an equalization filter keeping all the encoding paramteres as similar as possibile to the original ones.
-^ Video filter    | swresize, 1366x768, Bilinear  |
-^ Basic x264      | Preset: **slow** (or less), Tuning: **film**, Profile: **High**, IDC Level: **Auto** |
-^ Video encoding  | Average Bitrate (Two Pass), Average Bitrate 6000 kb/s (about 3 Gb per hour)  |
-^ Audio codec     | <del>Lame MP3</del> Vorbis  |
-^ Audio bitrate   | CBR 192 (or higher)  |
-We can use **Avidemux** to make the final rendering (re-encoding). For a **comman line only** solution you can consider ffmpeg to perfomr the re-encoding and **mkvmerge** (contained into the **mkvtoolnix** Debian package) to merge all into a Matroska container.
+The video clips were **extracted from the original MP4 container** as **[[wp>MPEG transport stream|MPEG-TS]]** snippets containing only video (no audio). To re-encode each clip we used the following **ffmpeg** recipe:
-==== AVC (x264) is better than ASP (xvid4) ====
+<code bash>
+#!/bin/sh
+#
+# Re-encode video clips in MPEG transport stream (MPEG-TS) format applying
+# some saturation and gamma correction.
+#
+# saturation:           In range 0.0 to 3.0. The default value is "1".
+# gamma_{r|g|b}         In range 0.1 to 10.0. The default value is "1".
+INPUT="$1"
+OUTPUT="$INPUT.eq.ts"
+EQ_FILTER="eq=saturation=0.88:gamma_r=0.917:gamma_g=1.007:gamma_b=1.297"
+# Produces MPEG segments like the ones produced by the SJCAM SJ8Pro:
+ffmpeg -i "$INPUT" \
+    -vf "$EQ_FILTER" \
+    -codec:v libx264 \
+    -preset veryslow -profile:v main -level:v 4.2 -pix_fmt yuvj420p \
+    -x264-params 'vbv-maxrate=38000:vbv_bufsize=20000:nal-hrd=vbr:force-cfr=1:keyint=8:bframes=0:scenecut=-1:ref=1' \
+    -keyint_min 8 -brand avc1 -f 3gp \
+    -bsf:v h264_mp4toannexb -f mpegts \
+    "$OUTPUT"
+</code>
+The gamma correction for the three RGB channels was determined with the GIMP, using the //Colors// => //Levels// => //Pick the gray point for all channels// tool. The use of MPEG-TS clips allowed the montage of the final video by just concatenating them.
+===== AVC (x264) is better than ASP (xvid4) =====
 See this page: **[[https://www.avidemux.org/admWiki/doku.php?id=general:common_myths|Common myths]]** to understand the differences between formats (standards) and codecs (pieces of software). Read also this simple page: **[[https://www.cyberlink.com/support/product-faq-content.do?id=1901|Difference between MPEG-4 AVC and MPEG-4 ASP]]**. See also the Wikipedia article about **[[wp>Advanced Video Coding]]**.
@@ Line 503: / Line 523: @@
 </code>
+====== ffmpeg: leggere la sequenza di VOB da un DVD ======
+Nella directory **VIDEO_TS** di un DVD la traccia principale è normalmente suddivisa in file numerati sequenzialmente, ad esempio: ''VTS_01_0.VOB'', ''VTS_01_1.VOB'', ...
+In teoria è sufficiente concatenare i file in un solo file destinazione e quindi trattarlo come un normale file audio/video. Tuttavia è possibile indicare i singoli file come input senza la necessità di occupare ulteriore spazio disco con questa sintassi:
+<code bash>
+SOURCE="concat:VTS_01_1.VOB|VTS_01_2.VOB|VTS_01_3.VOB|VTS_01_4.VOB|VTS_01_5.VOB"
+ffmpeg -i "$SOURCE" ...
+</code>
+====== ffmpeg: impostare un ritardo sui sottotitoli durante il muxing ======
+Se un flusso di sottotitoli (ad esempio nel formato Picture based DVD) non indica correttamente l'offset iniziale di riproduzione è possibile dire ad ffmpeg di impostarlo opportunamente in fase di muxing. In questo esempio il primo sottotitolo appare a 44.5 secondi:
+<code bash>
+ffmpeg -i video-stream.mkv -i audio-stream.mkv -itsoffset 44.5 -i subtitles-stream.mkv ...
+</code>
+In generale dovrebbe essere possibile scoprire l'offset quando ffmpeg legge l'intero stream, al momento in cui trova il prmio frame dei subtitles mostra qualcosa del genere sulla console:
+<code>
+[mpeg @ 0x55f98bb2c6c0] New subtitle stream 0:7 at pos:14755854 and DTS:44.5s
+</code>
+====== Parameters for final rendering ======
+See the page **[[ffmpeg_final_rendering]]**.
 ====== Doppiaggio audio con Ardour ======
 Vedere la pagina dedicata: **[[ardour_dubbing]]**.