Video convertion options: what's their meaning?

[monteverde]

Hello everyone,
I make some MOV to MP4 convertions using the Video-to-video converter (free). The conversions worked good.

I first tryed convertion with these options:

* MP4 Movie
* Lenght: 19,886
* Quality: custom
* Video codec: mpeg4
* Video size: original
* Video aspect: auto
* Video bitrate: 1024
* Video framerate: auto
* Audio codec: aac
* Audio bitrate: 128
* Audio sample rate: 44100
* Audio channels: 2 stereo
* Sync A/V: no
* Audio stream index: default
* Volume: 1/8
* Target filesize: unlimited
* Two pass encoding: no
* Deinterlace: no
* Keep aspect: yes

And then I got a 2,86 MB file
Changing the Quality option to "Same as source" I got a 53,7 MB file
Changing the Quality option to "Lowest" (which also moves the Video and Audio bitrates to 1732 and 64, respectively), I got a 4,37 MB file
And finally, changing the Quality option to "Highest" (which also changes the Video bitrate to 10400), I got a 25,0 MB file

Well, I'm absolutely a newbie in video processing, so I've a poor comprehension about those options. Playing the converted files, I discarded the "lowest" and the "custom" files: artifacts are too much noticeable.
But I found it difficult noticing any differences between the "highest" and the "same as source" files. And between these and the original MOV file. By the way there is a very big difference between file sizes:

"highest" is a 25 MB file
"same as source" is a 54 MB file
the original movie is a 59 MB file

I would ask you if there are some tips which can help me in choosing the "quality" option in this conversion (and in the future ones, also).
Furthermore, are there some options (other than the "quality" one) I can/have to change, to get good MOV to MP4 conversions?

Thanks everybody for your care


Now I append some other technical info about the original MOV file:
--- Source info ------------------------------------------------------------------------------
- General
- Complete name : MVI_3112.MOV
- Format : MPEG-4
- Format profile : QuickTime
- Codec ID : qt
- File size : 58.8 MiB
- Duration : 19s 887ms
- Overall bit rate : 24.8 Mbps
- Video
- ID : 1
- Format : AVC
- Format/Info : Advanced Video Codec
- Format profile : Baseline@L4.1
- Format settings, CABAC : No
- Format settings, ReFrames : 1 frame
- Format settings, GOP : M=1, N=15
- Codec ID : avc1
- Codec ID/Info : Advanced Video Coding
- Duration : 19s 887ms
- Bit rate : 23.2 Mbps
- Width : 1 280 pixels
- Height : 720 pixels
- Display aspect ratio : 16:9
- Frame rate mode : Constant
- Frame rate : 29.970 fps
- Color space : YUV
- Chroma subsampling : 4:2:0
- Bit depth : 8 bits
- Scan type : Progressive
- Bits/(Pixel*Frame) : 0.841
- Stream size : 55.1 MiB (94%)
- Language : English
- Color primaries : BT.709-5, BT.1361, IEC 61966-2-4, SMPTE RP177
- Transfer characteristics : BT.709-5, BT.1361
- Matrix coefficients : BT.601-6 525, BT.1358 525, BT.1700 NTSC, SMPTE 170M
- Audio
- ID : 2
- Format : PCM
- Format settings, Endianness : Little
- Format settings, Sign : Signed
- Codec ID : sowt
- Duration : 19s 887ms
- Bit rate mode : Constant
- Bit rate : 1 536 Kbps
- Channel(s) : 2 channels
- Channel positions : Front: L R
- Sampling rate : 48.0 KHz
- Bit depth : 16 bits
- Stream size : 3.64 MiB (6%)
- Language : English
------------------------------------------------------------------------------------------------

[DB83]

Filesize is determined by file-length * bitrate.

The 'Same as Source' option attempts to apply the same bitrate from your original video to the new one. The others use presets with different bitrates.

There is a similar topic about this program that was on the forum a few days ago. Look it up and you will see how you can over-ride these presents to use your own bitrate.

[Krispy Kritter]

Which to choose is a matter of personal preference, as only you can decide what is an acceptable output. And based on your selection, whether it saves enough space to justify the time spent converting.

[Cornucopia]

You need to determine WHAT you really want to do, and WHY. Do you just want an MP4 re-wrapped into an MOV. That's easy, with no loss, but you'll end up with ~same filesize. Do you rather need something a particular size and or bitrate? Could that be because of the device you're going to be using it with?

More info...

Scott

[monteverde]

Thanks all for your replies,

I would understand why these two converted files:

"highest" (25 MB)
"same as source" (54 MB)

have such a different file sizes. although they seem to have the same video quality (the original MOV file size is 59 MB).

My purpose is to convert from MOV to MP4 without any quality loss (if it's possible) so I can view movies on my TV set (it only plays MP4 format, while my camera made only MOV files).

I'm not care about convertion speed, but I would save space on my pen drive, if this choice doesn't decay the overall video quality.

So, can I choose the "highest" convertion option? Or I have the convert with the "same as source"?

Thanks for your care

[Cornucopia]

Well, there's "without ANY quality loss" (which basically re-uses the original material, or uses a lossless alternate codec) and then there's "without any NOTICEABLE quality loss" (where you determine the bitrate and get a certain quality-VBR/CBR, or you determine the quality and get whatever bitrate fits-CQ/CRF). There is loss, but you might not notice it.
In your example, "same as source" could actually be a re-use (re-wrapped), with the difference being in the container overhead or more likely with a change in audio quality/bitrate. Or it could just be a near approximation of the bitrate of the original.
"Highest" just means highest that it will allow you to manually set the settings. This may or may not be the actual highest that the encoder can produce. This may or may not look "the same" as the other, to YOU (which can vary greatly - to me, the 25Mbps could look like CRAP compared to the other).

MOV->MP4 is extremely easy in QTPro or ffmpeg (just re-wrapping), if the video & audio are ALREADY within MP4 specs. If NOT, you would have to re-encode anyway.

Scott

[monteverde]

Thanks for your kind answer.

Now I would ask you for some other questions, about my thread. I'll appreciate you if you can answer some of these.

1) What is the relationship between the "video", "audio" and "overall" bit rates?

Here are the "video bit rate" values:
ORIGINAL FILE: 23.2 Mbps
LOWEST: 1 773 Kbps
HIGHEST: 10.4 Mbps
CUSTOM: 1 074 Kbps
SAME AS SOURCE: 22.5 Mbps

And these are the "audio bit rate" values:
ORIGINAL FILE: 1 536 Kbps
LOWEST: 66.2 Kbps
HIGHEST: 128 Kbps
CUSTOM: 128 Kbps
SAME AS SOURCE: 128 Kbps

Overall bit rates:
ORIGINAL FILE: 24.8 Mbps
LOWEST: 1 845 Kbps
HIGHEST: 10.5 Mbps
CUSTOM: 1 207 Kbps
SAME AS SOURCE: 22.6 Mbps

2) All of the converted files have audio bit rates much smaller than the original file. Can this ruin the audio quality?

3) What's the meaning of the "bits/(pixel*frame)" values, I got in my convertions?
ORIGINAL FILE: 0.841
LOWEST: 0.064
HIGHEST: 0.377
CUSTOM: 0.039
SAME AS SOURCE: 0.816

4) The original MOV audio has a PCM audio format, while all of the converted files have an AAC audio format. Can this ruin the audio quality?

5) Some of the audio bit rate modes are labeled "constant", while others are labeled "variable". What is the difference between "constant" and "variable"?
ORIGINAL FILE: constant
LOWEST: constant
HIGHEST: variable
CUSTOM: variable
SAME AS SOURCE: variable

6) Although the source audio sampling rate is 48.0 KHz, all converted files have sampling rate=44.1 KHz. Can this setting ruin audio quality?

7) There are different distributions between video stream sizes and audio stream sizes. Why are there those differences?
ORIGINAL FILE: 94% video + 6% audio
LOWEST: 96% video + 4% audio
HIGHEST: 99% video + 1% audio
CUSTOM: 89% video + 11% audio
SAME AS SOURCE: 99% video + 1% audio

8) What is the meaning of the "deinterlace= no" convertion option?

9) What is the meaning of the "two pass encoding= no" convertion option?

10) What is the meaning of the "sync A/V= no" convertion option?

THANKS everybody for your care

[Selur]

What is the relationship between the "video", "audio" and "overall" bit rates?

video + audio bit rate + subtitles = overall bit rate, at least here since MediaInfo isn't aware of the concept of container overheads. (since they can't be derived from the headers or a file)

2) All of the converted files have audio bit rates much smaller than the original file. Can this ruin the audio quality?

It does not have to, but yes it can ruin things.
Since most compressions are lossy compressions you will nearly always loose some quality, even if you use the same or higher bit rates.
(that still does not mean that reencoding must ruin things)

3) What's the meaning of the "bits/(pixel*frame)" values, I got in my convertions?

it's a statistical value and it simply indicates how many bits were spend in average for each pixel per frame (some people take it as a general indicator for quality; personally I wouldn't)

4) The original MOV audio has a PCM audio format, while all of the converted files have an AAC audio format. Can this ruin the audio quality?

Like mentioned before, each lossy compression will lower the quality, but does not have to ruin thins.

5) Some of the audio bit rate modes are labeled "constant", while others are labeled "variable". What is the difference between "constant" and "variable"?

variable = bit rate of each audio frame is the changing depending on the content
constant = bit rate of each audio frame is the same independent of the content
unless the constant bit rate is required due to some standard, or the constant bit rate is as high as the maximal variable bit rate, variable bit rate normally is preferred

6) Although the source audio sampling rate is 48.0 KHz, all converted files have sampling rate=44.1 KHz. Can this setting ruin audio quality?

Depending on how good the resampling is done it can ruin the quality, but it does not have to.
you might want to read up on general signal processing: http://en.wikipedia.org/wiki/Sampling_%28signal_processing%29

There are different distributions between video stream sizes and audio stream sizes. Why are there those differences?

because audio and/or video bit rates (or container overhead) did change

What is the meaning of the "deinterlace= no" convertion option?

it means the source content should not be deinterlaced -> http://www.100fps.com/

What is the meaning of the "two pass encoding= no" convertion option?

it means a one pass encoding scheme was/should be used

What is the meaning of the "sync A/V= no" convertion option?

no special treatment for audio/video synchronization was / should be done