[FFmpeg-user] Fixed GOP encoding for HLS

[Andrew Sinclair]

Thanks for the tip and getting closer

As if I use:

ffmpeg -i 131375031.mp4 -vcodec libx264 -b:v 500k -r 24 -coder 0 -profile:v
baseline -force_key_frames
00:00:06.000,00:00:12.000,00:00:18.000,00:00:24.000,00:00:30.000,00:00:36.000,00:00:42.000
out_gop12_forcekeyframes.ts

I get a much better m3u8 (not sure how the segmenter rounding works...) as
the iframes look spot on.

Would be great if there was a way to just specify every x seconds.


#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-ALLOWCACHE:1
#EXTINF:6.034289,
out_seg6-000.ts
#EXTINF:6.005422,
out_seg6-001.ts
#EXTINF:6.013578,
out_seg6-002.ts
#EXTINF:6.021744,
out_seg6-003.ts
#EXTINF:6.003789,
out_seg6-004.ts
#EXTINF:6.011944,
out_seg6-005.ts
#EXTINF:6.020111,
out_seg6-006.ts
#EXTINF:6.002156,
out_seg6-007.ts
#EXTINF:6.010322,
out_seg6-008.ts
#EXTINF:6.018478,
out_seg6-009.ts
#EXTINF:6.627456,
out_seg6-010.ts
#EXTINF:6.141233,


Also what do you mean by "Don't turn of the scenecut frames"?

Agreed half sec too small was just experimenting and there is a note in the
-segment docs suggesting 1/2*frame_rate this which may need fixing


On 5 December 2012 15:19, Anatol <anatol2002 at gmail.com> wrote:

> Your command line does not 'force' key-frame every 12 frames, it just
> 'recommends' it. Default ffmpeg settings has 'scenecut' key-frames
> generation. This option is vital for preserving video quality. In order to
> 'force' key frames at certain rate u actually have to spell-out the exact
> timings that u want them to appear at. Use 'froce_keyframes' command line
> option. DON'T turn of the scenecut key frames.
>
> By the way half sec GOPs are by far much too small, this also
> can degrade the quality. 2-3 sec is enough.
>
> On Wed, Dec 5, 2012 at 1:15 AM, Andrew Sinclair <ajsinclair at gmail.com
> >wrote:
>
> > Hi,
> >
> > I am trying to encode and segment for Apple HLS devices and am look for
> any
> > tips from anyone that has mastered this.
> >
> > I am trying to get the segments in the .m3u8 files to be exactly aligned
> > for so that each segment is precisely 6 seconds long and I have
> experience
> > with encoders that do this quite well as I suspect that not being aligned
> > is causing issues on an Android device I am working on.
> >
> > To get this aligned I am encoding with frame rate 24 and a min/max GOP of
> > 12 (based on notes in the ffmpeg docs on the -segment command) however I
> > still see variation in the segment size.
> >
> > Can anyone tell me what the optimal settings for this are? Does anyone
> know
> > how the segments end up not aligned if I am forcing requesting keyframes
> > every 12 frames and this shows up in ffprobe?
> >
> > Example encode:
> > ffmpeg -i 131375031.mp4 -vcodec libx264 -b:v 500k -r 24 -g 12 -keyint_min
> > 12 -coder 0 -profile:b baseline out_gop12.ts
> >
> > Example segment:
> > ffmpeg -i out_gop12.ts -codec copy -map 0  -f segment -segment_list
> > playlist_gop12.m3u8 -segment_time 6 out_gop12_seg6-%03d.ts
> >
> > Resulting index file extract (note the segment lengths vary a lot!):
> > #EXTM3U
> > #EXT-X-VERSION:3
> > #EXT-X-MEDIA-SEQUENCE:0
> > #EXT-X-ALLOWCACHE:1
> > #EXTINF:7.719244,
> > out_gop12_seg6-000.ts
> > #EXTINF:4.750000,
> > out_gop12_seg6-001.ts
> > #EXTINF:6.125000,
> > out_gop12_seg6-002.ts
> > #EXTINF:6.541667,
> > out_gop12_seg6-003.ts
> > #EXTINF:9.333333,
> > out_gop12_seg6-004.ts
> > #EXTINF:1.750000,
> > out_gop12_seg6-005.ts
> > #EXTINF:6.666667,
> > out_gop12_seg6-006.ts
> > #EXTINF:6.166667,
> > out_gop12_seg6-007.ts
> > #EXTINF:5.166667,
> > out_gop12_seg6-008.ts
> > #EXTINF:6.625000,
> > out_gop12_seg6-009.ts
> > #EXTINF:6.541667,
> > out_gop12_seg6-010.ts
> > #EXTINF:6.291667,
> > out_gop12_seg6-011.ts
> > #EXTINF:9.583333,
> > out_gop12_seg6-012.ts
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> >
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