[FFmpeg-user] ffmpeg latency and lag combining audio and video on Raspberry Pi

[Neik]

On 2015-06-12 19:43, Lou wrote:
> On Fri, Jun 12, 2015, at 04:32 AM, Neik wrote:
>> I am trying to stream combined audio and video from a Raspberry Pi.
>> 
>> To capture video alone I use:
>> 
>> raspivid -o - -t 0 -n -w 1280 -h 720 -fps 25 | ffmpeg 
>> -thread_queue_size
>> 1024 -y -f h264 -framerate 25 -i - -vcodec copy -f mpegts
>> udp://44.0.0.95:1234
> 
> Console output missing.
> 
>> It takes 6 seconds for the streaming status line to appear. The video
>> then lags reality by about 2.3 seconds
>> 
>> Why does this delay occur? How can I reduce it to zero?
>> 
>> To combine video and audio I use:
>> 
>> raspivid -o - -t 0 -n -w 1280 -h 720 -fps 25 | ffmpeg 
>> -thread_queue_size
>> 1024 -y -f h264 -framerate 25 -i - -thread_queue_size 512 -f alsa -ac 
>> 1
>> -i hw:1 -vcodec copy -acodec mp3 -f mpegts udp://44.0.0.95:1234
>> 
>> The output is
> 
> Complete console output missing. This is required information.
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VIDEO ONLY:

It takes 6 seconds for the streaming status line to appear. The video 
then lags reality by about 2.3 seconds

root at raspberrypi:~# raspivid -o - -t 0 -n -w 1280 -h 720 -fps 25 | 
ffmpeg -thread_queue_size 1024 -y -f h264 -framerate 25 -i - -vcodec 
copy -f mpegts udp://44.0.0.95:1234
ffmpeg version N-72834-gfd004e1 Copyright (c) 2000-2015 the FFmpeg 
developers
   built with gcc 4.6 (Debian 4.6.3-14+rpi1)
   configuration: --enable-libmp3lame
   libavutil      54. 27.100 / 54. 27.100
   libavcodec     56. 41.100 / 56. 41.100
   libavformat    56. 36.100 / 56. 36.100
   libavdevice    56.  4.100 / 56.  4.100
   libavfilter     5. 16.101 /  5. 16.101
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  2.100 /  1.  2.100
Input #0, h264, from 'pipe:':
   Duration: N/A, bitrate: N/A
     Stream #0:0: Video: h264 (High), yuv420p, 1280x720, 25 fps, 25 tbr, 
1200k tbn, 50 tbc
Output #0, mpegts, to 'udp://44.0.0.95:1234':
   Metadata:
     encoder         : Lavf56.36.100
     Stream #0:0: Video: h264, yuv420p, 1280x720, q=2-31, 25 fps, 25 tbr, 
90k tbn, 25 tbc
Stream mapping:
   Stream #0:0 -> #0:0 (copy)
frame=  363 fps= 39 q=-1.0 size=   13020kB time=00:00:14.52 
bitrate=7345.9kbits/s

VIDEO AND AUDIO:

5.5 seconds to "Stream #0:0:", then a pause of 6.2 seconds. Audio lags 
2s, audio 10.4s

root at raspberrypi:~# raspivid -o - -t 0 -n -w 1280 -h 720 -fps 25 | 
ffmpeg -thread_queue_size 1024 -y -f h264 -framerate 25 -i - 
-thread_queue_size 512 -f alsa -ac 1 -i hw:1 -vcodec copy -acodec mp3 -f 
mpegts udp://44.0.0.95:1234
ffmpeg version N-72834-gfd004e1 Copyright (c) 2000-2015 the FFmpeg 
developers
   built with gcc 4.6 (Debian 4.6.3-14+rpi1)
   configuration: --enable-libmp3lame
   libavutil      54. 27.100 / 54. 27.100
   libavcodec     56. 41.100 / 56. 41.100
   libavformat    56. 36.100 / 56. 36.100
   libavdevice    56.  4.100 / 56.  4.100
   libavfilter     5. 16.101 /  5. 16.101
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  2.100 /  1.  2.100
Input #0, h264, from 'pipe:':
   Duration: N/A, bitrate: N/A
     Stream #0:0: Video: h264 (High), yuv420p, 1280x720, 25 fps, 25 tbr, 
1200k tbn, 50 tbc
Guessed Channel Layout for  Input Stream #1.0 : mono
Input #1, alsa, from 'hw:1':
   Duration: N/A, start: 1434111432.388990, bitrate: 768 kb/s
     Stream #1:0: Audio: pcm_s16le, 48000 Hz, 1 channels, s16, 768 kb/s
Output #0, mpegts, to 'udp://44.0.0.95:1234':
   Metadata:
     encoder         : Lavf56.36.100
     Stream #0:0: Video: h264, yuv420p, 1280x720, q=2-31, 25 fps, 25 tbr, 
90k tbn, 25 tbc
     Stream #0:1: Audio: mp3 (libmp3lame), 48000 Hz, mono, s16p
     Metadata:
       encoder         : Lavc56.41.100 libmp3lame
Stream mapping:
   Stream #0:0 -> #0:0 (copy)
   Stream #1:0 -> #0:1 (pcm_s16le (native) -> mp3 (libmp3lame))
frame=715263 fps= 25 q=-1.0 size=27703638kB time=07:56:50.52 
bitrate=7932.3kbits/s