Differences

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--- doc:appunti:linux:video:ffmpeg [2023/01/07 15:18] – [Final rendering (re-encoding)] niccolo
+++ doc:appunti:linux:video:ffmpeg [2024/07/25 08:12] (current) – [AVC (x264) is better than ASP (xvid4)] niccolo
@@ Line 262: / Line 262: @@
 ./kenburst-1-make-images "$INPUT_FILE" "$KBURST_GEO" "$DURATION_S" \
     | ./kenburst-2-make-video "$OUTPUT_MP4"
-</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:
-^ Video codec     | MPEG-4 AVC (x264)  |
-^ 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 4096 kb/s (about 1.8 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 **command line only** solution you can consider **ffmpeg** to perfomr the re-encoding and to make the merge (mux) all into a Matroska container.
-<code bash>
-TITLE="Balcani, maggio 2022"
-ffmpeg \
-    -i "video-high-quality.mkv" \
-    -i 'audio-music.ogg' -i 'audio-live.ogg' \
-    -map '0:v:0' -map '1:a:0' -map '2:a:0' \
-    -metadata title="$TITLE" -metadata:s:v:0 title="$TITLE" \
-    -metadata:s:a:0 title="Accompagnamento musicale" \
-    -metadata:s:a:1 title="Audio in presa diretta" \
-    -filter:v "scale=1366x768" -aspect "16:9" \
-    -vcodec 'libx264' -pix_fmt 'yuvj420p' -preset 'veryslow' -tune 'film' -profile:v 'high' -level:v 5 \
-    -acodec copy \
-    "$DST_FILE"
 </code>
@@ Line 325: / Line 297: @@
 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) ====
+===== 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 341: / Line 313: @@
   * **Tuning**: Use the **film** option for real life scenes.
   * **Profile**: The **High** profile is OK for high-definition television (e.g. 1280×720, or Blu-ray disc), //High 10// add support for 10 bits per sample, //High 444// up to 14 bits per sample (both for [[wp>High dynamic range|HDR]] videos). Do not use //Main//, which is for standard-definition TV, e.g. 720×576.
-  * **IDC Level**: Leave this parameter to **Auto**, setting it to higer values does not increase the video quality, but imposes higher constraints to the decoder. I.e. to decode 1280×1024@42 it is sufficient the 3.1 IDC level (see [[wp>Advanced Video Coding]]).
+  * **IDC Level**: Leave this parameter to **Auto**, setting it to higer values does not increase the video quality, but imposes higher constraints to the decoder. I.e. to decode a 1280×720@30 stream it is sufficient the 3.1 IDC level, to decode a 1920×1080@30 stream (max 20 Mbps) it is required the 4 IDC level (see [[wp>Advanced Video Coding]]).
 ====== More on ffmpeg Command Line ======
@@ Line 551: / 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]]**.