DV AVI to AVC MP4 transcoding

[Paul Anderegg]

I have done a lot of searching online for an answer, but really can't find a specific answer to my query. I found a very similar thread here, but it took a turn into another direction before the original question was answered.

I shoot television news on DVCPRO25. I ingest with Vegas, resulting in your standard NTSC DV widescreen AVI file. To get the video to air, I transcode to AVC MP4 720x480 29.97p 1.212 aspect ratio at 6Mbps. This results in file sizes that are acceptable for downloading and broadcast, but the video is noticeably fuzzy. I need rendering specs for the highest quality AVC MP4 file I can make, with regard to the original source files quality.

I think my rendering specs, besides the progressive conversion, are spot on, but I would really like to know the recommended bit rate for preserving the full quality of the 25Mbps DV video. There are times that I need to send the highest quality video possible, but due to bandwidth and internet speed limitations, uploading/downloading of original 25Mbps files is impractical. So, what Mbps bit rate should I use to render MP4 files as close to the originals quality as possible?

Paul Anderegg

[poisondeathray]

Are you blend deinterlacing? That would make things "fuzzy." Vegas doesn't have very good deinterlacing, but when set to "interpolate" it willl yield more crisp results than "blend"

For "broadcast" - you don't really mean broadcast do you? You wouldn't use 29.97p, you would be using interlaced 29.97i (or 59.94i , it's the same thing, just different naming conventions)

Also, there are better encoders than the ones vegas use (mainconcept or sony avc) that offer better compression - x264 . Many people export out a lossless intermedate then use a gui for x264 (e.g. megui, ripbot, handbrake), or use a frameserver like debugmode frameserver

Many people also make use of better deinterlacers through avisynth, instead of vegas' deinterlacers - results are also noticably better . But these things take extra steps and extra processing power- sometimes a quicker turnaround with medium quality is more acceptable for ENG type scearnios than higher quality and compression with a slower turnaround

The "appropriate" bitrate you use depends on source complexity - harder to compress material will require more bitrate (e.g. lots of motion, noise, details ). Static content like "talking heads" or interviews will require much less bitrate for similar levels of "quality". You cannot use a set value for all types of content . This is how long GOP compression works - the differences between frames are stored - when there are lots of differences (noise, motion) it requires a lot more bitrate. Something static like a blank wall will require very little maybe 10-20x less . So "what bitrate should I use" is not a question that can be answered appropriately. Another benefit of x264 is the option of quality based encoding - you set a certain quality level, and the appropriate average quantizer is given - so too much bitrate isnt allocated, nor is too little allocated

[Paul Anderegg]

By "broadcast" I do mean broadcast. My clients obviously air as 720p or 1080i depending on affiliation. Thanks for the "convention" info, I kept wondering why my ingested AVI files all say 29fps!

As for deinterlacing, I have no idea. I have spent countless hours trying different rendering options on Vegas trying to duplicate a standard 720x480 59i MP4. I ended up modifying a Sony AVC template at 720x480 1.212 29.97, and selecting progressive under the "field order" tab. Anytime I attempted to render anything as interlaced, I would get those annoying horizontal lines that are hideous whenever there is panning or movement, totally unairable. Anyway, when I say fuzzy, I really mean "soft" or lower resolution. Below is a link to a sample clip.....

http://sandiegonewssource.com/wp-content/uploads/2012/08/081912ADL.mp4

As for bit rate, we all know DV is constant bit rate of 25Mbps. Can you recommend a constant bit rate for MP4 that would match the peak quality of a DV AVI file? I am just looking to render a smaller size MP4 file that will keep up the quality and use less MB from the better compression algorithm available via AVC.

As for x264 or any other "exotic" flavor of MP4, I think I have to stick to what I am using now. Each TV station can handle only certain file types depending on what NLE they use, and the AVC thing works well because they can all accept and edit it without issue. If you want to help me out a little more in depth, I would love it if I could link you a test AVI file that you could render in Vegas and possibly shoot me the best custom template data for rendering either the 6Mbps (my download standard) or a top quality Mbps. If you don't have Vegas it would be easy enough to download the 30 day trial one.....all depending on if you have the free time to help me out? My vegas rendering dialog has about 500 custom templates I ended up creating to test, and I can't figure out how to delete the ones I don't want! Yikes.

Paul Anderegg

[poisondeathray]

I didn't have a look at your file, but interlace is normal. You better clarify what your client wants/needs

Interlace is normal. Those lines are normal. DV is interlaced. SD content is broadcast interlaced. All equipment can handle interlaced footage (HDTV, CRT TV's, blu-ray, DVD, set top boxes) . Footage is deinterlaced by progressive displays

Usually broadcast requirements for SD footage is interlaced 720x480i59.94 (or 720x480i29.97 , again same thing) . They usually have requirements on the compression used, minimum bitrate used, and probably don't want a tiny AVC file, and definitely don't want a progressive (deinterlaced) file

But in Web delivery , most interlaced footage is deinterlaced . If it's the final footage for webpage embedding, then you usually want a tiny , deinterlaced progressive file (low bandwidth is preferrable) . If it's an intermediate, then clarify what the webmaster or your client wants.

As for recommending a bitrate - maybe you missed that part above. There is no recommendation because it's impossible to set a correct bitrate for everything. I suggest you read that section again. Anyways there are usually requirements that stations need, and just follow those guidelines

[Paul Anderegg]

OK, lets do some experimenting...

My two biggest customers are ABC and NBC, one 720p, the other 1080i. I will modify my standard 6Mbps p template as an i template. As stated, I would like the MP4 to be as close to exact specs and observable quality as possible.

I have chosen a 20 second clip of an emergency vehicle passing my camera with lights and siren......this will be a good trial and error clip that will show any motion artifacts. Here are my options as Vegas allows me to adjust..

AVC or Memory Stick?

NTSC 720x480

Profile main or high?

Frame rate 29.97 (NTSC) or 59.94(Double NTSC)

Field order upper or lower field first or progressive?

Pixel aspect 1.2121

Bit rate 6Mbps

Thanks in advance for your time!

Paul Anderegg

[poisondeathray]

Again, you should clarify what they want.

They usually won't accept files with certain specs. There will be a "minimum requirement" sheet that you download, usually a PDF .

SD content wouldn't be deinterlaced for a news station or broadcast in North America (US or Canada)

Unless you're doing this as a recreational, non-professional submission (like random user posted videos) , I think you are going about this wrong, unless you have special consideration or written exemption (certain programmes are allow exemptions)

[Paul Anderegg]

Well, the point is mute.....I tried altering the template from progressive to interlaced, both upper and lower field first, and Vegas gives "An invalid argument was specified" error.

The local and national broadcasters haven't complained about the quality so far, so obviously they don't care. I am just a stickler for quality, and wanted my stuff to look it's best. I will just create a 12.5Mbps MP4 progressive template and cut the file size in half and hope that retains full DV quality.

Thanks for your time.

Paul Anderegg

[poisondeathray]

All I can say is wow. Maybe they have relaxed all their guidelines?

A small local station probably wouldn't mind, but your location says San Diego....

Anyways, if you want a deinterlaced file, the project properties would be the same as the DV NTSC template (widescreen if your content is 16:9) . Set deinterlace to "interpolate". "blend" makes everything blurry (it mixes the fields 50-50 mix)


For render settings profile high, framerate 29.97 (this throws away 1/2 the information,59.94 is called "bobbing", but usually isn't used for web or broadcast , and if it was broadcast you would normally leave it interlaced) . Single rate deinterlacing will look "choppy" and won't retain the motion smoothness as the original , while "bobbing" or double rate deinterlacing will

field order => this is where vegas decides to deinterlace or not. If you set it to progressive it will deinterlace, for SD DV source and rendering interlaced you would leave it bottom field first

For AVC, you would rarely need more than 9-10Mb/s for SD footage (even with vegas), unless it was very difficult to compress footage (lots of motion , action, noise, detail)



If you want to view interlaced footage on a PC, you need to activate the deinterlacer (some formats will be automatically deinterlaced, others will not be) . You wouldn't see "lines" that you were complaining about when viewed normally. That's what it will look like when it's broadcast. Interlace is just a way of saving bandwidth (that's why it was an implemented standard for broadcast)

[jagabo]

Your video looked about normal for a standard definition camcorder. Apply a sharpening filter if you want a sharper picture. You'll get more oversharpening halos though. Otherwise, get an HD camcorder if you want a sharper picture.

[Paul Anderegg]

Regarding interlaced AVC video......Vegas won't allow it. If I select any f the field options instead of progressive, I get an error dialog and it won't render.

As far as broadcast quality, I created a template the same as my download stuff, and just selected the highest bitrate allowed, 16Mbps. To my eyes, it looks indistinguishable from the original, but the files are much smaller in size.

As for getting an HD camera, that would actually hurt my video. I can't even work with downloadable full res SD files much less the size required for HD. And also, they don't make full size HD cameras with low light sensativity of an old SD cam.

Paul

[_Al_]

Regarding interlaced AVC video......Vegas won't allow it.

I have here Vegas Pro v.8.0c and it is working, MainConcept mpeg4-avc, I had to change profile to Main, it lets me to choose upper field first or lower field first ...

[Paul Anderegg]

I have been using a new 16Mbps .mp4 template, and wanted to run it by everyone to see if it can be improved. As stated before, I am transcoding DVCPRO25 16:9 to AVC .mp4. Here is what my current template is set up as......

AVC, NTSC 720x480, Profile Main, entropy CABAC, frame rate 29.970 progressive, pixel ratio 1.2121, bit rate 16,000,000.

I have tried to keep as many "specs" the same as possible, and would like to render 59.94 interlaced so that it matches the original, but the AVC template doesn't seem to want to support that option. I don't understand what a main profile is, or what entropy is. To best transcode to .mp4 from my original .avi, should these settings be altered in any way?

Thanks!

Paul

[jagabo]

h.264 profiles: http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Profiles

CABAC: http://en.wikipedia.org/wiki/Context-adaptive_binary_arithmetic_coding

[Paul Anderegg]

That answered my question! I will ignore the DVB aspect, and it appears that "main" is the correct setting for my mp4 files.

Here is an unusual question. If my video will eventually be broadcast in HD, and since I have to transcode it to mp4 for delivery anyway, would there be any quality difference between a 720x480 30p and a 1280x720 30p transcoded from the same DVCPRO25 avi at the same 16Mbps bit rate?

Paul

[jagabo]

From what I hear Vegas isn't very good at scaling interlaced video. I would leave it SD and let them upscale when broadcast.