[libav-tools] AVI(ac3): Broken sound after copy

Mathieu Malaterre mathieu.malaterre at gmail.com
Mon Apr 6 14:02:01 CEST 2015


On Sat, Apr 4, 2015 at 6:48 PM, Luca Barbato <lu_zero at gentoo.org> wrote:
> On 04/04/15 15:23, Mathieu Malaterre wrote:
>> Hi,
>>
>> I am trying to understand why avconv is breaking sound on a working
>> AVI input. I can play a video on my FreeBox V5 just fine. However
>> after copy:
>>
>> $ avconv -i input.avi -codec copy output.avi
>>
>> The generated `output.avi` appears as non working on my FreeBox V5
>> player. If I compare (avprobe -show_streams) here is what I see:
>>
>> $ avprobe -show_streams input.avi > /tmp/1
>> $ avprobe -show_streams output.avi > /tmp/2
>> $ diff -u /tmp/1 /tmp/2
>> --- /tmp/1 2015-04-04 15:13:53.222288651 +0200
>> +++ /tmp/2 2015-04-04 15:19:19.898275904 +0200
>> @@ -26,15 +26,15 @@
>>  codec_long_name=ATSC A/52A (AC-3)
>>  codec_type=audio
>>  codec_time_base=1/48000
>> -codec_tag_string=[0] [0][0]
>> -codec_tag=0x2000
>> +codec_tag_string=[254][255][0][0]
>> +codec_tag=0xfffe
>>  sample_rate=48000.000000
>>  channels=6
>>  bits_per_sample=0
>>  r_frame_rate=0/0
>> -avg_frame_rate=125/4
>> -time_base=1/56000
>> +avg_frame_rate=0/0
>> +time_base=4/125
>>  start_time=0.000000
>>  duration=N/A
>> -nb_frames=127391040
>> +nb_frames=33174
>>  [/STREAM]
>>
>> Does the `codec_tag_string` value have any influence here ?
>
> I think so, if you add -tag:a 0x2000 does it work?

Now I have:

$ diff -u /tmp/1 /tmp/2
--- /tmp/1 2015-04-06 13:50:25.906181310 +0200
+++ /tmp/2 2015-04-06 13:55:36.833418214 +0200
@@ -35,7 +35,7 @@
 bits_per_sample=0
 avg_frame_rate=0/0
 bit_rate=448000.000000
-time_base=1/56000
+time_base=4/125
 start_time=0.000000
 duration=N/A
 nb_frames=127391040

However I can still not hear a thing on the generated file...

In summary, none of the following generates a file with working sound
(while input.avi is ok):

$ avconv -i input.avi -codec copy test_copy.avi
$ avconv -i input.avi -codec copy -tag:a 0x2000 test_copy.avi

Thanks for comments,


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