[FFmpeg-user] m3u8 seeking accuracy

[Paul B Mahol]

On 11/28/16, Louis Letourneau <lletourn49 at gmail.com> wrote:
> I seem to be having issues seeking accurately in HLS videos.
>
> ffmpeg version 3.2 and master N-82664-g801b5c1
>
> If I create an HLS video like this
> mkdir 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 120 a/a.m3u8
>
>
> And also create it's mp4 counterpart:
> ffmpeg -i a/a.m3u8 -codec copy a.mp4
>
>
> And try to seek in any segment:
> F=130;rm -f f.png;ffmpeg -y -ss `awk "BEGIN {print (${F})/25}"` -i a/a.m3u8
> -f image2 -q:v 1 -vframes 1 f.png ; feh f.png
>
> Got frame 250
>
> F=126;rm -f f.png;ffmpeg -y -ss `awk "BEGIN {print (${F})/25}"` -i a/a.m3u8
> -f image2 -q:v 1 -vframes 1 f.png ; feh f.png
>
> Got frame 250
>
> F=125;rm -f f.png;ffmpeg -y -ss `awk "BEGIN {print (${F})/25}"` -i a/a.m3u8
> -f image2 -q:v 1 -vframes 1 f.png ; feh f.png
>
> Got frame 125 (good)
>
> F=124;rm -f f.png;ffmpeg -y -ss `awk "BEGIN {print (${F})/25}"` -i a/a.m3u8
> -f image2 -q:v 1 -vframes 1 f.png ; feh f.png
>
> Got frame 125
>
>
> Now try the same with the mp4 and you'll always get the exact right frame
> F=130;rm -f f.png;ffmpeg -y -ss `awk "BEGIN {print (${F})/25}"` -i a.mp4 -f
> image2 -q:v 1 -vframes 1 f.png ; feh f.png
>
> Got 130 (good)
>
> F=126;rm -f f.png;ffmpeg -y -ss `awk "BEGIN {print (${F})/25}"` -i a.mp4 -f
> image2 -q:v 1 -vframes 1 f.png ; feh f.png
>
> Got 126 (good)
> etc
>
> it seems to be seeking on segment boundaries only.
>
> Of course, if I put -ss after the input '-i' I seek accurately but it takes
> much longer since it's decoding all the frames.
>
> Is this a bug or I am missing a parameter?

It's missing feature iirc, if this is static file you could create
index once and use it for precise seeking after.


>
> Thanks
> Louis
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