Add ffmpeg

ffmpeg.md

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+Oneliners (e afins) uteis de FFMPEG pra lembrar
+
+* Converter SSA pra SRT
+``` 
+for f in *.ssa; do ffmpeg -i "$f" "${f%.ssa}.srt"; done 
+ ```
+ * Extrair legendas embarcadas no container de video (sem ocr, só funciona com formatos de texto)
+```
+EXT=mkv;
+for F in *${EXT}; do 
+    while read L FI SI LN SF; do
+        [[ -z $LN ]] && continue;
+        L=$(( L - 1 )); 
+        FN=${F%.$EXT}.$LN.srt;
+        ffmpeg -i "$F" -map $FI:s:$L -c:s srt tmp.srt;
+
+        sed -e 's/<[^>]*>//g' -e 's/{[^}]*}//g' tmp.srt > "$FN";
+        rm tmp.srt;
+        read FI SI LN SF <<< '';
+    done < <(ffprobe "$F" 2>&1 | sed -nr '/Subtitle:/s/^.*Stream #([0-9]):([0-9])\(([a-z-]+)\).*Subtitle: ([a-z]+) .*$/\1 \2 \3 \4/p' | cat -n); 
+done;
+```