[FFmpeg-user] Fixed GOP encoding for HLS

[Steven Liu]

2012/12/5 Andrew Sinclair <ajsinclair at gmail.com>:
> Looks like the frames are getting out of sync after the first 6 or so (see
> below which is ffprobe via python formatting). I have also attached a
> sample m3u8 off an Envivio encoder below which has the keyframes right on
> 10 secs
>
> I will have a play with the current options but having the ability to force
> a keyframe at a specified interval would be ideal for this purpose.
>
> I Frame: 0
>
> I Frame: 3
>
> I Frame: 12
>
> I Frame: 24
>
> I Frame: 36
>
> I Frame: 48
>
> I Frame: 60
>
> I Frame: 72
>
> I Frame: 83
>
> I Frame: 95
>
> I Frame: 107
>
> I Frame: 110
>
> I Frame: 119
>
> I Frame: 131
>
> I Frame: 143
>
> I Frame: 155
>
> I Frame: 167
>
> I Frame: 179
>
> I Frame: 185
>
> I Frame: 191
>
> I Frame: 203
>
> I Frame: 215
>
> I Frame: 227
>
> I Frame: 239
>
> I Frame: 245
>
> I Frame: 251
>
> I Frame: 263
>
> I Frame: 275
>
> I Frame: 287
>
> I Frame: 299
>
> I Frame: 311
>
> I Frame: 323
>
> I Frame: 335
>
>
> #EXT-X-MEDIA-SEQUENCE:4826
>
> #EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:21:50Z
>
> #EXTINF:10,
>
> 20121203T065726-1200-4826.ts
>
> #EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:22:00Z
>
> #EXTINF:10,
>
> 20121203T065726-1200-4827.ts
>
> #EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:22:10Z
>
> #EXTINF:10,
>
> 20121203T065726-1200-4828.ts
>
> #EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:22:19Z
>
> #EXTINF:10,
>
> 20121203T065726-1200-4829.ts
>
> #EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:22:29Z
>
> #EXTINF:10,
>
> 20121203T065726-1200-4830.ts
>
>
>
> On 5 December 2012 11:00, Stefano Sabatini <stefasab at gmail.com> wrote:
>
>> On date Wednesday 2012-12-05 10:15:46 +1100, Andrew Sinclair 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
>>
>> Can you confirm that the resulting ts has the timestamp at the exact
>> location? Or in other words, are you sure that -g 12 -keyint_min 12
>> produces a fixed GOP of 12 frames (ffprobe -show_packets or
>> -show_frames should confirm this).
>>
>> > 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!):
>>
>> The trick I used was using -force_key_frames in ffmpeg and then use a
>> reasonable value for -segment_time_delta (half the value of the
>> framerate should be safe), check the segment examples.
>>
>> We could eventually extend -force_key_frames to accept an expression,
>> in case specifying 0,6,12,... etc. is awkward.
>> --
>> FFmpeg = Fast Fancy Merciless Peaceful Elegant Guide

Full output message please!

Do you want to split the 3s a segment, 12s a segment

the result like bellow:

#EXT-X-MEDIA-SEQUENCE:4826

#EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:21:50Z

#EXTINF:3,

20121203T065726-1200-4826.ts

#EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:22:00Z

#EXTINF:12,

20121203T065726-1200-4827.ts

#EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:22:10Z

#EXTINF:24,

20121203T065726-1200-4828.ts

#EXT-X-PROGRAM-DATE-TIME:2012-12-03T20:22:19Z

#EXTINF:36,

20121203T065726-1200-4829.ts


Is that you mean?