As a follow up, if anyone wants to enable and use fast (index) seeking in HLS videos while they are being transcoded, the secret is to use the -hls_playlist_type event parameter as mentioned in the doc here: https://ffmpeg.org/ffmpeg-all.html#toc-Options-38 This feature was added decembre 2015 so it's been in the 3.2 branch for awhile now. Louis On Fri, May 19, 2017 at 5:49 PM, Louis Letourneau <lletourn49@gmail.com> wrote:

Just a question before I start diving in the code, why doesn't fast seeking work on live hls feeds/streams/files?

Context: If you create a dummy video: mkdir -p a;ffmpeg -y -s 640x480 -f rawvideo -pix_fmt rgb24 -r 25 -i /dev/zero -vf "drawtext=fontfile=/usr/share/fonts/truetype/freefont/FreeMono.ttf: text=%{n}: x=(w-tw)/2: y=h-(2*lh): fontcolor=white: box=1: boxcolor=0x000000FF" -an -vcodec libx264 -preset medium -tune stillimage -crf 24 -pix_fmt yuv420p -shortest -force_key_frames "expr:gte(t,n_forced*5)" -bf 0 -hls_time 5 -hls_list_size 0 -hls_wrap 0 -hls_allow_cache 1 -hls_segment_filename "a/a_%04d.ts" -t 9999 a/a.m3u8

let it encode and in another terminal try to seek (once the encoding passed the time you want to seek to)

ffmpeg -v info -ss 00:00:10 -y -live_start_index 0 -i a/a.m3u8 -f image2 -vframes 1 a.png ; feh a.png

You'll get in the logs a/a.m3u8: could not seek to position 11.400

and then ffmpeg will decode all frames until the asked frame.

If you quit the encoder and seek again, it fast seeks immediately (jumps to the right segment and decodes te right frame). It doesn't need to fo through all the segments.

My question is, if the segments (.ts) are already there and the manifest, m3u8 already shows that they are there, why doesn't fast seeking work?

Thanks Louis