[FFmpeg-user] Generating HLS chunks on demand

Vincent Deconinck vdeconinck at gmail.com
Wed Jan 25 01:59:31 EET 2023


Hi Cyril,

Thanks a lot for your reply.

I tried your suggestion and changed my first test to do frame accurate
seeking by moving the -ss option upfront, like so:
ffmpeg -ss 0 -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
-t 4 -f mpegts sample_fa-0.ts
ffmpeg -ss 4 -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
-t 4 -f mpegts sample_fa-1.ts
ffmpeg -ss 8 -i .source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
-t 4 -f mpegts sample_fa-2.ts
ffmpeg -ss 12 -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
-t 4 -f mpegts sample_fa-3.ts
ffmpeg -ss 16 -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
-t 4 -f mpegts sample_fa-4.ts

I then wrapped up the following m3u8:
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:4
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:4.000000,
sample_fa-0.ts
#EXTINF:4.000000,
sample_fa-1.ts
#EXTINF:4.000000,
sample_fa-2.ts
#EXTINF:4.000000,
sample_fa-3.ts
#EXTINF:4.000000,
sample_fa-4.ts
#EXT-X-ENDLIST

Unfortunately, the playback in VLC stops after the first segment (and the
audio is cut even before that)

I wondered what the duration of the segments was, and using
ffprobe -v error -show_entries format=duration -of
default=noprint_wrappers=1:nokey=1 sample_fa-<n>.ts
with n = 0 to 4, it showed:
4.021333
4.021333
4.021333
4.021333
4.021333
So the duration for all segments is identical, but not exactly 4.000000
seconds. Could it be the reason ?

I also tried moving the "-t 4" option to the beginning too, just after the
-ss option, but it's even worse, because segment durations are variable
then:
4.021333
4.381333
4.781333
4.421333
4.341333
(and playback also stops after the first segment)

Do the TS segments have a specific "end of video" marker that would explain
why playback stops (and that marker should not be present in HLS segments) ?

Kind regards,


Vincent



On Tue, Jan 24, 2023 at 12:03 AM Cyril Comparon <cyril.comparon at gmail.com>
wrote:

> Hi Vincent
>
> I believe what you're looking for is frame-accurate seeking.
> To achieve that you have to do input seeking instead of output seeking. The
> former is achieved by specifying -ss before -i in your command line,
> whereas you're doing the latter by specifying -ss after -i.
> See https://trac.ffmpeg.org/wiki/Seeking
>
> HTH
> Cyril
>
> Le lun. 23 janv. 2023 à 09:15, Vincent Deconinck <vdeconinck at gmail.com> a
> écrit :
>
> > Hi,
> >
> > I performed more tests thinking that maybe the -f mpegts did not create
> > "hls-compliant" ts chunks (whatever that could mean).
> > So I tried creating first a full hls with the following command :
> > ffmpeg -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25 -f
> hls
> > -hls_time 4 sample.m3u8
> > This took a long time to process the full video of course, but the result
> > plays perfectly fine.
> > I then created a partial version limited to 12 seconds (=3 chunks of 4
> > secs) from the same source, as follows:
> > ffmpeg -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25 -t
> 12
> > -f hls -hls_time 4 sample_part.m3u8
> >
> > I performed a binary diff on the resulting ts files, and the chunks #0
> and
> > #1 are exactly the same.
> > However, chunk #3 (which is the last of the "partial" version) is
> different
> > (375kB vs 392kB) :
> >
> >   1578 sample.m3u8
> >    190 sample_part.m3u8
> > 582424 sample_part0.ts
> > 764972 sample_part1.ts
> > 383896 sample_part2.ts
> > 582424 sample0.ts
> > 764972 sample1.ts
> > 401004 sample2.ts
> > ...
> >
> > What is the reason for that difference, and how can I make sure I
> generate
> > a valid segment for those 4 seconds ?
> >
> > Kind regards,
> >
> > Vincent
> >
> > On Fri, Jan 20, 2023 at 5:44 PM Vincent Deconinck <vdeconinck at gmail.com>
> > wrote:
> >
> > > Hi,
> > > I have thousands of files that I would like to serve as HLS streams to
> a
> > > very small number of users (3-5), without having to process them all
> > > upfront. So I'm looking for a way to generate single HLS chunks (as
> > opposed
> > > to a full HLS package) only when they are requested.
> > > My problem is the resulting stream is choppy and basically unusable.
> > > Here are the commands I'm using::
> > >
> > > ffmpeg -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
> -ss
> > 0
> > > -t 4 -f mpegts cache\sample-0.ts
> > > ffmpeg -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
> -ss
> > 4
> > > -t 4 -f mpegts cache\sample-1.ts
> > > ffmpeg -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
> -ss
> > 8
> > > -t 4 -f mpegts cache\sample-2.ts
> > > ffmpeg -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
> -ss
> > > 12 -t 4 -f mpegts cache\sample-3.ts
> > > ffmpeg -i source.ts -c:v libx264 -b:v 1000k -c:a aac -b:a 128k -g 25
> -ss
> > > 16 -t 4 -f mpegts cache\sample-4.ts
> > >
> > > The m3u8 file is :
> > >
> > > #EXTM3U
> > > #EXT-X-VERSION:3
> > > #EXT-X-TARGETDURATION:4
> > > #EXT-X-MEDIA-SEQUENCE:0
> > > #EXTINF:4.000000,
> > > sample-0.ts
> > > #EXTINF:4.000000,
> > > sample-1.ts
> > > #EXTINF:4,000000,
> > > sample-2.ts
> > > #EXTINF:4,000000,
> > > sample-3.ts
> > > #EXTINF:4,000000,
> > > sample-4.ts
> > > #EXT-X-ENDLIST
> > >
> > > What am I doing wrong ?
> > >
> > > Kind Regards,
> > >
> > > Vincent
> > >
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