问题
I'm capturing a video by means of an USB Terratec Grabster AV350 (which is based on the em2860 chip).
I don't succeed to get the audio when it is played . If I play the captured video with vlc or with ffplay I got only 3 seconds sound and then a silence for the rest of the video ...
During the capturing I don't get any errors. At the end it indicates the size of the video and audio captured ....
I'm using the ffmpeg command for this :
ffmpeg -f alsa -ac 2 -i hw:3 -f video4linux2 -i /dev/video0 -acodec ac3 -ab 128k -vcodec mpeg4 -b 6000k -r 25 test5.avi
The log is :
[alsa @ 0x9bcd420]Estimating duration from bitrate, this may be inaccurate
Input #0, alsa, from 'hw:3':
Duration: N/A, start: 69930.998994, bitrate: N/A
Stream #0.0: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
[video4linux2 @ 0x9bf5d30]Estimating duration from bitrate, this may be inaccurate
Input #1, video4linux2, from '/dev/video0':
Duration: N/A, start: 1307111377.654173, bitrate: -2147483 kb/s
Stream #1.0: Video: rawvideo, yuyv422, 720x576, -2147483 kb/s, 1000k tbr, 1000k tbn, 1000k tbc
[ac3 @ 0x9bf9590]No channel layout specified. The encoder will guess the layout, but it might be incorrect.
Output #0, avi, to 'test5.avi':
Metadata:
ISFT : Lavf52.64.2
Stream #0.0: Video: mpeg4, yuv420p, 720x576, q=2-31, 6000 kb/s, 25 tbn, 25 tbc
Stream #0.1: Audio: ac3, 44100 Hz, stereo, s16, 128 kb/s
Stream mapping:
Stream #1.0 -> #0.0
Stream #0.0 -> #0.1
Press [q] to stop encoding
frame= 1283 fps= 25 q=2.3 Lsize= 38677kB time=51.32 bitrate=6173.9kbits/s
**video:37755kB audio:846kB** global headers:0kB muxing overhead 0.198922%
If I reduce the command for only capturing audio, then the audio file can be played successfully :
ffmpeg -f alsa -ac 2 -i hw:3,0 -acodec ac3 -ab 128k test5.avi
[alsa @ 0x8ede420]Estimating duration from bitrate, this may be inaccurate
Input #0, alsa, from 'hw:3,0':
Duration: N/A, start: 70395.998935, bitrate: N/A
Stream #0.0: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
[ac3 @ 0x8eebac0]No channel layout specified. The encoder will guess the layout, but it might be incorrect.
Output #0, avi, to 'test5.avi':
Metadata:
ISFT : Lavf52.64.2
Stream #0.0: Audio: ac3, 44100 Hz, stereo, s16, 128 kb/s
Stream mapping:
Stream #0.0 -> #0.0
Press [q] to stop encoding
size= 227kB time=13.62 bitrate= 136.8kbits/s
**video:0kB audio:213kB** global headers:0kB muxing overhead 6.902375%
If I run the command for only video capturing then vlc or ffplay can play the video successfully :
ffmpeg -f video4linux2 -i /dev/video0 -vcodec mpeg4 -b 12000k -r 25 test5.avi
[video4linux2 @ 0x91d6420]Estimating duration from bitrate, this may be inaccurate
Input #0, video4linux2, from '/dev/video0':
Duration: N/A, start: 1307112044.025687, bitrate: -2147483 kb/s
Stream #0.0: Video: rawvideo, yuyv422, 720x576, -2147483 kb/s, 1000k tbr, 1000k tbn, 1000k tbc
Output #0, avi, to 'test5.avi':
Metadata:
ISFT : Lavf52.64.2
Stream #0.0: Video: mpeg4, yuv420p, 720x576, q=2-31, 12000 kb/s, 25 tbn, 25 tbc
Stream mapping:
Stream #0.0 -> #0.0
Press [q] to stop encoding
frame= 388 fps= 25 q=2.0 Lsize= 12963kB time=15.52 bitrate=6842.5kbits/s
**video:12949kB audio:0kB** global headers:0kB muxing overhead 0.114584%
Strange behaviour I noticed is that when I tried capturing video and audio, I can not capture the audio afterwards any more, unless I unplug the AV350 first.
The G350 is located at card 3 :
htpc@htpc-01:/proc/asound/G350/pcm0c$ more info
card: 3
device: 0
subdevice: 0
stream: CAPTURE
id: USB Audio
name: USB Audio
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 1
subdevices_avail: 1
The OS is a Linux 2.6.38-8-generic with the Ubuntu Natty Narwhal version
Any help on how to tackle this issue would be great ....
Thanks !
回答1:
I was working on something like that and I used this command:
ffmpeg -y -f alsa -i default -f v4l2 -i /dev/video0 -acodec aac -strict -2 -ac 1 -b:a 64k -vcodec libx264 -b:v 300k -r 30 -g 30 prueba1.mp4
At the beginning I was having trouble with hw:3 component. Instead of that I put in default and the code actually worked. I hope this helps.
回答2:
I've found that using the command at the bottom works for an external USB webcam (mine is currently a Logitech C310). I used this command on my laptop, which already has a built in mic/webcam, and it still captured the audio and video from my C310. Obviously, change the /dev/video0 to fit your needs. You can use
ls /dev/video*
in terminal to see what video capture devices your OS has set up.
ffmpeg -f alsa -i default -itsoffset 00:00:00 -f video4linux2 -s 1280x720 -r 25 -i /dev/video0 out.avi
回答3:
It works for high quality video:
ffmpeg -f alsa -ac 2 -i hw:1,0 -f video4linux2 -i /dev/video0 -acodec ac3 -ab \
128k -f matroska -s 1280x720 -vcodec libx264 -preset ultrafast -qp 16 testsize.mkv
来源：https://stackoverflow.com/questions/6311560/how-can-i-capture-audio-and-video-simultenaous-with-ffmpeg-from-a-linux-usb-capt