Thanks for your help, we have finally solved the problem.
We used the following command:
ffmpeg -f alsa -i pulse -f video4linux2 -s 320x240 -i /dev/video0
-c:v mpeg2video -b:v 2M -r 15 -s 1280x720 -pix_fmt yuv420p -c:a
aac -b:a 64k -f mpegts -mpegts_service_id 0x70e0 -mpegts_flags
'latm' -pes_payload_size 188 -metadata service_name="ss_id"
-muxrate 5727280 example
With this we can generate a transport stream from the webcam with
constant bit rate.
It is important to mention that this transport stream is
compatible for a ISDB-T transmission with the following
parameters:
Guard Interval 1/16
Modulation scheme QPSK
Code rate 2/3
13 segments with a single layer
You can also use this command for any input video.
I assume you've calculated the TS bitrate from the ISDB-T
parameters you're using for transmission.
https://www.dibeg.org/faq/ref/c2-001.html
I'm not using ffmpeg. I have my own TS muxer. Unfortunately, I
developed it while employed, so I can't open source it.
You may want to add a VBV size to your command line. The
default is very small. Try:
-maxrate 2M -bufsize 9781248
This may cause a lot of "rc buffer underflow" errors. 2 Mbps is
a super low bitrate for HD MPEG-2 video. I would consider using
16 or 64QAM to get to a reasonable bitrate for HD of at least 7
Mbps or more.
Ron
On 10/3/19 15:29, Gastón Morales
wrote:
Hello Ron,
We are aware of the muxrate option to
set the correct bitrate for the transmission, but still we
are having problems with the reception.
We use the following command:
ffmpeg -i prueba.webm -c:v mpeg2video
-b:v 2M -r ntsc -s 1920x1080 -c:a aac -b:a 64k -f mpegts
-mpegts_service_id 0x70e0 -mpegts_flags 'latm'
-pes_payload_size 188 -metadata service_name="Brotola"
-muxrate 5727280 camara13seg.ts
Do you know if there is
anything wrong in this command, or if there is anything to add
to make it work properly?
We would really appreciate if you could share us the ffmpeg
command that you used in any of your examples.
Thanks
for your prompt response!
El 03/10/19 a las 18:53, Ron
Economos escribió:
To create a constant rate transport stream with ffmpeg, you
have to use the -muxrate parameter. The video stream does
not have to be CBR. However, the peak video rate plus the
audio rate cannot exceed the muxrate.
BTW, w6rz.net is my website. Most of the main page streams
are muxed at the ATSC rate of 19.392658 Mbps.
Ron
On 10/3/19 14:20, Gastón Morales
wrote:
Dear all,
We are a team of engineer students, working on a ISDB-T Digital TV Transmitter for GNU-Radio.
To test the TX, we need to create constant bit rate transport streams that are compatible with the ISDB-T standard.
Currently we are working with ffmpeg to transcode the videos that we want to send, but we are having some issues with the receptor, and we suspect that the videos that we are transcoding with ffmpeg are not constant bit rate videos.
We found the webpage http://www.w6rz.net that has some CBR samples taken out from DVB-T trasmissions.
Does anyone know how were those samples generated to mantain a constant bit rate?
Thank you!!
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