What H.264/H.265 video compression parameters provide DVD-equivalent quality with better compression

dvdffmpegh.264h.265video conversion

I have got a box of DVD video disks that I seek to get rid of while I'd like to keep the videos by converting them into MP4 files to store them on a hard drive.

Considering superiority of the modern H.264 AVC and H.265 HEVC compression algorithms over the DVD-standard MPEG2 I hope to save hard drive space by compressing the video while saving ~99% of the DVD original quality.

What

H.264 (FFMPEG + libx264) compression parameters
H.265 (FFMPEG + libx265) compression parameters

should I use to achieve my goal?

By parameters I mean the CBR/CRF values, the preset (no veryslow/placebo please), flags etc.

PS: I'd prefer to constraint the case with using -pix_fmt yuv420p and -profile:v baseline -level 3.0 to ensure the file plays OK on all the devices including old devices relying on old hardware decoder chips. Using somewhat increased I-frames frequency (using the -g parameter) is also desirable to facilitate low-speed and high-latency media usage.

For HEVC, I'd as well prefer using parameters that would ensure smooth hardware-accelerated playback on devices that support it but I don't mean to focus on this constraint as I haven't seen any devices offering hardware-accelerated H.265 decoding at all yet.

Best Answer

Note that for this, you should always use the latest ffmpeg version, and preferably compile it yourself. This gives you access to the most recent libx265 and libfdk-aac for audio encoding.

Also, the data rate savings will be quite drastic if you're going from a ~10 MBit/s DVD to around 1–2 MBit/s for H.264 video and 0.5–1 MBit/s for H.265 video. Changing the quality in the below steps may influence the bitrates, but still the data reduction should be significant.

H.264

For the quality / rate control, you want to use CRF mode in libx264 rather than a constant bitrate. Using CRF ensures that an average quality is preserved, independent of the original video resolution or its complexity. Constant bitrate is only really useful if you're constrained by the transmission medium (e.g. hard drive speed, Internet throughput).

Choosing the CRF value is the tricky part. It requires you to look at the output. The default for libx264 (23) offers a quite good tradeoff between size and quality. But given that your original source is already compressed (and not with a very good quality compared to Blu-rays), you may want to change the CRF to be a little lower, such as 20. This will increase needed bitrate by about a third.

Choose the preset according to how long you want to wait. slow seems like a good value here.

ffmpeg -i input \
-c:v libx264 -crf 20 -pix_fmt yuv420p \
-x264-params keyint=240:min-keyint=20 \
-preset:v slow -profile:v baseline -level 3.0 \
-c:a libfdk_aac -vbr 4 \
output.mp4

The built-in ffmpeg AAC encoder can be used if libfdk-aac is not available. Use -c:a aac -strict experimental -b:a 128k instead of -c:a libfdk_aac -vbr 4.

H.265

Research suggests that using HEVC will lead to up to 74% bitrate saving compared to H.264. This is based on subjective viewing data of Ultra-HD sequences. Of course, it depends on the temporal complexity of the source content, and the amount of data saved will not be as high for hard to code sequences. Either way you can safely say that 50% data reduction is absolutely possible.

The default CRF for libx265 is 28. Using the same source content, it results in about half the bitrate compared to libx264 at CRF 23. This is irrespective of the actual bitrate, i.e., if the H.264 version takes 1.5 MBit/s, then H.265 will use around 750 kBit/s, but it's 750 kBit/s vs. 350 kBit/s for another sequence. I ran it on a couple of sequences at DVD-PAL resolution and was not able to tell the difference in terms of quality.

ffmpeg -i input \
-c:v libx265 -pix_fmt yuv420p \
-x265-params crf=28:keyint=240:min-keyint=20 \
-preset:v slow \
-c:a libfdk_aac -vbr 4 \
output.mp4

For more information, here are the relevant resources:

FFmpeg Wiki on H.264 encoding and H.265 encoding
ffmpeg documentation on libx265
x265 documentation

Better quality for MPEG-2

You have a few options if you want to stick with MPEG-2:

Increase the bitrate. You're now using -b:v 2500k. If it's HD video, you will not get far with only 2.5 MBit/s. You need at least double that or even more to make the result look good. For example, use -b:v 6000k -target pal-dvd.

For 720p, I think that you should still use a higher bitrate. Remember that DVDs use MPEG-2 and come in about 4.7 GB for 2hrs of movie, so you end up with around 5–8 MBit/s. MPEG-2 is really not very compression-efficient and works better at higher bitrates.
Use a specific quality setting. Change -b:v … to -qscale:v 2. The number here ranges from 1 to 31 and higher means lower quality. There's no point going beyond 4 or 5. If you don't care for the bitrate start with 2 and see if that works for you.

Messing with the number of B-frames, motion estimation method or GOP size may tweak the quality a little but won't result in big changes.

Silent audio

Use -f lavfi -i aevalsrc=0 to generate a silent audio stream. For example:

ffmpeg -i "in.wmv" -f lavfi -i aevalsrc=0 -shortest -c:v mpeg2video -qscale:v 2 -c:a libmp3lame "out.mpg"

You may need to add -target pal-dvd to the above command to force a certain buffer size.

I chose MP3 as codec. MPEG files cannot contain audio other than MPEG Layer I and II audio as well as PCM streams, so using a silent Ogg Vorbis file will not work unless you convert the audio stream as well (which is not what you're doing when you use -c:a copy).

Use a different video codec

I'm surprised that a TV that plays video files will read MPEG-2 but not anything else. At least MPEG-4 Part II video should be supported (that's what you know as "DivX" – an MPEG-4 Part II encoder). So you could try:

ffmpeg -i "in.wmv" -f lavfi -i aevalsrc=0 -shortest -c:v libxvid -qscale:v 2 -c:a libmp3lame "out.mp4"

Your TV might actually also support H.264, but only a certain profile. Try using the baseline profile, for example:

ffmpeg -i "in.wmv" -f lavfi -i aevalsrc=0 -shortest -c:v libx264 -profile:v baseline -crf 23 -c:a aac -strict experimental "out.mp4"

In the above example I've used the CRF option to set the quality instead of qscale. See the H.264 encoding guide for more.

Windows 10 – Getting HEVC H.265 Codec for Hardware Acceleration

From what I found, the Quick for Desktop (Windows10) does support the import and playback of HEVC files, but it lacks Hardware acceleration for those HEVC files when you have a Desktop PC with a dedicated graphics card where you cannot switch between integrated and dedicated graphics as you can on a laptop, as often suggested as a solution.

Consequently, I think that for hardware acceleration you need to wait for an update to GoPro Quik. This capability is simply missing in the software and there is no setting to be turned on.