sderenzi
7th August 2007, 18:30
Hi!
I've got a bizarre question, one that makes no sense to me. Recently I wanted to try repacking some AAC songs into new mp4 containers, I gave mp4box a go. I downloaded it, ran the mp4box -raw 1 and extracted my audio from the mp4 files. Later I added the RAW AAC back into mp4 containers using mp4box -add. The question I've come accross is this and it's a weird one... once I'd done this I tested the audio to see if it would play, it did. The odd thing was the bitrate being reported was not the original 128, it was now like 118?! I was completely confused since mp4box doesn't do encoding, it should just be copying the AAC stream into a new container.... this makes me wonder if the file is alright or if it actually lost some quality / bitrate somehow. I mean as far as I know there is nothing, and I mean nothing, that would cause a 128 bitrate to drop just cuz I repacked it using mp4box. Any ideas? It's completely perplexing to me, and then when I check the actual bitrate I see one for on-the-fly basically, it reports the bitrate isn't constant even though it's a CBR???
What am I seeing here ppl, is this normal or what? Is the new mp4 to be trusted or did mp4box somehow lower the bitrate? How could it when it's not re-encoding anything?
My thoughts are perhaps the original 128 bitrate was merely some sort of lie, maybe the RAW AAC stream itself was 118 while the container somehow made it appear to be different?
I've got a bizarre question, one that makes no sense to me. Recently I wanted to try repacking some AAC songs into new mp4 containers, I gave mp4box a go. I downloaded it, ran the mp4box -raw 1 and extracted my audio from the mp4 files. Later I added the RAW AAC back into mp4 containers using mp4box -add. The question I've come accross is this and it's a weird one... once I'd done this I tested the audio to see if it would play, it did. The odd thing was the bitrate being reported was not the original 128, it was now like 118?! I was completely confused since mp4box doesn't do encoding, it should just be copying the AAC stream into a new container.... this makes me wonder if the file is alright or if it actually lost some quality / bitrate somehow. I mean as far as I know there is nothing, and I mean nothing, that would cause a 128 bitrate to drop just cuz I repacked it using mp4box. Any ideas? It's completely perplexing to me, and then when I check the actual bitrate I see one for on-the-fly basically, it reports the bitrate isn't constant even though it's a CBR???
What am I seeing here ppl, is this normal or what? Is the new mp4 to be trusted or did mp4box somehow lower the bitrate? How could it when it's not re-encoding anything?
My thoughts are perhaps the original 128 bitrate was merely some sort of lie, maybe the RAW AAC stream itself was 118 while the container somehow made it appear to be different?