HDMI audio out from V1

Stephen Armour · August 28th, 2008, 07:45 AM

We are trying to find someone that knows the answer to this:

Since the V1 also compresses the audio for the HDV format, and we do NOT want compressed audio for our productions, we are looking for a way to bypass that compression.

Our major question is: does taking data through the HDMI port on the V1 bypass the compression?

We have a portable recording solution for pulling HDMI video coming down (we live in Brazil), but are not sure if the audio comes in uncompressed as well. If so, we are light years ahead with synced audio. If not, we need to make major modifications to our HDMI video/audio recorder.

Please don't answer this question unless you know the answer for sure.

Stephen Armour · August 28th, 2008, 11:11 AM

Someone has stated that the audio is UNCOMPRESSED through the HDMI, but can anyone confirm this for sure?

Logan McMillan · November 30th, 2008, 07:52 PM

Hey man,

What do you use to record your HDMI audio? Do you have a small portable device?

Hugh Mobley · December 1st, 2008, 07:14 AM

I have asked this same question in past threads, no it does not, hdmi out is raw tape. In the V1 I have not found a way to bypass the tape. even going thru a blackmagic card. which I thought if you taped live thru a card directly to a harddrive. All other threads in the past say no, can't get past the tape

John Cline · December 1st, 2008, 06:21 PM

I am 100% certain that the video coming out of the HDMI port on the V1 during a live capture is straight from the camera section and taken before the 1920x1080 to 1440x1080 rescaling and HDV compression and is an uncompressed 4:2:2 video stream. The audio stream coming out of the HDMI port is also uncompressed, but the question seems to be whether it might have gone through an MPEG audio compression/decompression cycle before it got to the HDMI port.

It may be easy enough to check; there is a 15Khz brickwall audio filter applied before compressing to MPEG audio and recording to tape. In fact, it is quite likely that this brickwall filtering is part of the MPEG compression software algorithm and not done in hardware. This effect of this 15Khz filter can be easily seen on a spectrum analyzer in any number of audio editing programs. If one were to capture live from HDMI and look at the audio, if the 15Khz rolloff isn't present, one could be certain that the audio is uncompressed. I've got a V1 and a Blackmagic Intensity card, I'll run this experiment when I get back to the office.

August 28th, 2008, 07:45 AM	#1
Stephen Armour Major Player Join Date: Dec 2005 Location: Natal, RN, Brasil Posts: 900	HDMI audio out from V1 - uncompressed? We are trying to find someone that knows the answer to this: Since the V1 also compresses the audio for the HDV format, and we do NOT want compressed audio for our productions, we are looking for a way to bypass that compression. Our major question is: does taking data through the HDMI port on the V1 bypass the compression? We have a portable recording solution for pulling HDMI video coming down (we live in Brazil), but are not sure if the audio comes in uncompressed as well. If so, we are light years ahead with synced audio. If not, we need to make major modifications to our HDMI video/audio recorder. Please don't answer this question unless you know the answer for sure. __________________ http://lightinaction.org "All in the view of the LION"

August 28th, 2008, 11:11 AM	#2
Stephen Armour Major Player Join Date: Dec 2005 Location: Natal, RN, Brasil Posts: 900	Someone has stated that the audio is UNCOMPRESSED through the HDMI, but can anyone confirm this for sure? __________________ http://lightinaction.org "All in the view of the LION"

December 1st, 2008, 07:14 AM	#4
Hugh Mobley Major Player Join Date: Nov 2006 Location: Placentia, Calif Posts: 549	I have asked this same question in past threads, no it does not, hdmi out is raw tape. In the V1 I have not found a way to bypass the tape. even going thru a blackmagic card. which I thought if you taped live thru a card directly to a harddrive. All other threads in the past say no, can't get past the tape __________________ Hugh Mobley www.petplanetvideos.com http://exposureroom.com/members/hmobley.aspx/

November 30th, 2008, 07:52 PM	#3
Logan McMillan Regular Crew Join Date: May 2007 Location: Christchurch, New Zealand Posts: 85	Hey man, What do you use to record your HDMI audio? Do you have a small portable device?

December 1st, 2008, 06:21 PM	#5
John Cline Major Player Join Date: Oct 2002 Location: Albuquerque, New Mexico USA Posts: 333	I am 100% certain that the video coming out of the HDMI port on the V1 during a live capture is straight from the camera section and taken before the 1920x1080 to 1440x1080 rescaling and HDV compression and is an uncompressed 4:2:2 video stream. The audio stream coming out of the HDMI port is also uncompressed, but the question seems to be whether it might have gone through an MPEG audio compression/decompression cycle before it got to the HDMI port. It may be easy enough to check; there is a 15Khz brickwall audio filter applied before compressing to MPEG audio and recording to tape. In fact, it is quite likely that this brickwall filtering is part of the MPEG compression software algorithm and not done in hardware. This effect of this 15Khz filter can be easily seen on a spectrum analyzer in any number of audio editing programs. If one were to capture live from HDMI and look at the audio, if the 15Khz rolloff isn't present, one could be certain that the audio is uncompressed. I've got a V1 and a Blackmagic Intensity card, I'll run this experiment when I get back to the office.