[FFmpeg-user] HTTP playlist stream copy to an IP QAM modulator

[Anacelia Sarlo]

Hello,
      I'am receiving an HTTP playlist stream (.m3u8 with H.264/AAC
elementary streams) and want to do a stream copy (no transcoding) and mux
the
output with mpeg-ts format, ideally in real time. This output is received
by an IP QAM modulator and then distributed to the cable network (DVB).

This is the ffmpeg command :

ffmpeg -re -y -i $stream  -c copy -f mpegts -map 0:0 -map 0:1
-mpegts_pmt_start_pid 66 -streamid 1:71 -streamid 0:70 udp://
192.168.1.108:1234?pkt_size=1316

When I watch the stream from the cable network,  the audio is OK but the
video looks sometimes faltering and other times too fast, and out of sync.
But when I received this same output with ffplay it runs OK.
It seems there is a problem with the time base, I did many testings with
(genpts, copyts, etc)  with no good results.

The IP QAM provider said that it can receive a variable bit rate stream,
but I heard that most IP QAMs works just with constant bit rates.
I have the following questions :

1. Does the ffmpeg command is correct for my intention ?
2. In case I have to generate a constant bit rate, how can I do that ? is
it necessary to transcode ?

Thanks for any suggestions!

Ana