If I convert an audio file with an album cover thank's to:
ffmpeg -i sample1.flac -ar 48000 -vn -c:a libvorbis -b:a 320k sample1.ogg
My sample1.ogg file doesn't have any album cover. Is there a way to ask explicitly to ffmpeg to keep the cover ?
Sum up of answers I found: Remove the option -vn which means: no video, because thumbnail are frame of video. Use libtheora instead of libvorbis. If you get a bitrate error, remove option -b:a 320k. At the end we get:
ffmpeg -i file.flac -c:v libtheora -q:v 10 -c:a libvorbis file.ogg
This gives you a file with an audio and a video content.
If you prefer to extract thumbnail in a separate file (to re-add it later for example), use:
ffmpeg -i file.flac -an -vcodec copy thumbnail.jpg
Thank's to Баяр Гончикжапов for his help and answers!