Re-encode 60fps to 30fps

2025-09-02 14:06 UTC gpt-5-thinking Open in ChatGPT ↗

You

ffmpeg command to re-encode a 4096X4096 60fps video to 30fps without altering its quality.

ChatGPT

If you just want to halve the framerate from 60 fps to 30 fps but keep the same codec/quality settings, you can tell ffmpeg to drop frames without re-encoding, or re-encode if needed.

Option 1 – No re-encoding (fast, no quality loss)

If your player and format allow it:

ffmpeg -i input.mp4 -vf fps=30 -c:v copy -c:a copy output.mp4

⚠️ Many formats don’t support changing framerate without re-encoding, so this may fail or desync audio.

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Option 2 – Re-encode, keeping near-original quality

This ensures a proper 30 fps stream but requires re-encoding. To avoid visible quality loss:

ffmpeg -i input.mp4 -r 30 -c:v libx264 -crf 18 -preset veryslow -c:a copy output.mp4

• -r 30 → sets output framerate.
• -c:v libx264 → H.264 encoder (use libx265 for HEVC if you prefer).
• -crf 18 → visually lossless constant quality (lower = higher quality, bigger file).
• -preset veryslow → maximizes efficiency (smaller file at same quality, but slower encode).
• -c:a copy → copies audio untouched.

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✅ If your goal is literally “same quality, just 30fps”, I recommend Option 2 with CRF 18. If you want mathematically lossless re-encode (huge files), replace the encoder with:

-c:v libx264 -qp 0

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Do you want me to give you the lossless re-encode command (exact pixel-perfect, huge file), or a visually lossless CRF version (smaller but still transparent)?

You

The bitrate must be around 50-70 Mb/s

ChatGPT

Got it ✅ — you want to re-encode to 30fps while fixing the video bitrate around 50–70 Mb/s.

Here’s the proper ffmpeg command:

ffmpeg -i input.mp4 -r 30 -c:v libx264 -b:v 60M -maxrate 70M -bufsize 140M -preset veryslow -c:a copy output.mp4

Explanation:

• -r 30 → output framerate at 30 fps
• -c:v libx264 → use H.264 encoder (you can switch to libx265 if you want HEVC)
• -b:v 60M → target average bitrate = 60 Mb/s
• -maxrate 70M → cap bitrate at 70 Mb/s
• -bufsize 140M → controls VBV buffer, usually set to 2× maxrate for smoother bitrate control
• -preset veryslow → maximizes compression efficiency at that bitrate
• -c:a copy → audio is untouched

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⚡ Notes:

• If you want constant bitrate (CBR) instead of average, add -minrate 60M -maxrate 60M -b:v 60M -bufsize 120M.
• If you prefer HEVC (H.265), just replace libx264 with libx265 — files will be smaller at same quality/bitrate, but encoding is slower.

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👉 Do you want me to make the command strict CBR (fixed ~60 Mb/s always), or is a VBR around 50–70 Mb/s good enough?

You

can the same command be run using cuda hwaccel ?

ChatGPT

Yes 👍 — you can use NVIDIA’s hardware encoder (NVENC) to accelerate encoding with CUDA.
That means replacing libx264 with h264_nvenc (or hevc_nvenc if you want HEVC).

Here’s the equivalent command using NVENC at ~60 Mb/s average:

ffmpeg -hwaccel cuda -i input.mp4 -r 30 -c:v h264_nvenc -b:v 60M -maxrate 70M -bufsize 140M -preset p7 -c:a copy output.mp4

Explanation of differences:

• -hwaccel cuda → uses GPU for decoding (optional, speeds up if your GPU supports it).
• -c:v h264_nvenc → NVIDIA’s hardware H.264 encoder.
• -b:v 60M -maxrate 70M -bufsize 140M → same bitrate logic as before (avg ~60 Mb/s, capped at 70).
• -preset p7 → NVENC quality preset (p1 fastest, p7 best quality).
• -c:a copy → keeps audio untouched.

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⚡ Notes:

• If you prefer HEVC, just switch to -c:v hevc_nvenc.
• NVENC doesn’t support CRF like software x264/x265 — it’s bitrate-based (CBR or VBR).
• Quality at the same bitrate is usually a bit lower than libx264 -crf, but still very good and much faster.

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👉 Do you want me to show you both CBR and VBR NVENC commands (so you can choose depending on your workflow)?

You

[h264 @ 00000201a7ac5800] decoder->cvdl->cuvidCreateDecoder(&decoder->decoder, params) failed -> CUDA_ERROR_INVALID_VALUE: invalid argument [h264 @ 00000201a7ac5800] Using more than 32 (39) decode surfaces might cause nvdec to fail. [h264 @ 00000201a7ac5800] Try lowering the amount of threads. Using 16 right now. [h264 @ 00000201a7ac5800] Failed setup for format cuda: hwaccel initialisation returned error.

ChatGPT

[Unsupported Content]

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[Unsupported Content]

ChatGPT

That error is from NVDEC (CUDA decoding) init — not the encoder. It usually happens when the decoder allocates too many decode surfaces (often amplified by threaded decoding) or when the input/profile isn’t supported by your GPU/driver build.

Here are reliable fixes, from simplest to strictest:

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1) Keep NVENC, disable CUDA decoding (most robust)

Decode on CPU and only use the GPU to encode. This avoids the NVDEC issue entirely and is still fast.

ffmpeg -threads 4 -i input.mp4 \
-r 30 -c:v h264_nvenc -b:v 60M -maxrate 70M -bufsize 140M -preset p7 \
-c:a copy output.mp4

(Change to -c:v hevc_nvenc if you prefer HEVC.)

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2) Use CUDA decode, but reduce surfaces/threads

Limit decoder threads and keep frames on the GPU cleanly:

ffmpeg -hwaccel cuda -hwaccel_output_format cuda -extra_hw_frames 8 -threads 1 -i input.mp4 \
-r 30 -c:v h264_nvenc -b:v 60M -maxrate 70M -bufsize 140M -preset p7 \
-c:a copy output.mp4

Tips:

• -threads 1 tames surface allocation.
• -extra_hw_frames 8 gives NVENC some breathing room without going past NVDEC limits.

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3) (Legacy) Force the CUVID decoder and set surfaces

If your build still has h264_cuvid, you can directly cap surfaces:

ffmpeg -c:v h264_cuvid -surfaces 20 -i input.mp4 \
-r 30 -c:v h264_nvenc -b:v 60M -maxrate 70M -bufsize 140M -preset p7 \
-c:a copy output.mp4

Note: h264_cuvid is deprecated in newer FFmpeg builds; prefer #1 or #2.

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Extra checks / gotchas

• Resolution/format support: H.264 NVENC is 8-bit only; if your source is 10-bit H.264 (rare) or a high-profile oddity, use CPU decode or switch to hevc_nvenc for 10-bit.
• 4096×4096 limit: That’s the upper H.264 limit for many GPUs. If you hit a cap, try -c:v hevc_nvenc.
• Filters: If you add CPU-only filters (e.g., fps), FFmpeg may auto insert hwdownload/hwupload. To be explicit, keep it simple with -r 30 at output as shown.
• Drivers/FFmpeg build: Make sure NVIDIA drivers and FFmpeg were built with CUDA/NVENC support.

If you still see the NVDEC error, stick with Option 1 (CPU decode + NVENC encode) — it’s the least fragile and will still hit your ~60 Mb/s target.

You

for some reason the generated file cannot be played at all on macos

ChatGPT

Got it — that’s a common pain point 😅.
macOS’s built-in players (QuickTime, Finder preview, Safari) are very picky about H.264/H.265 profiles, levels, and container settings. NVENC by default produces a stream that plays fine on VLC but not on Apple’s native decoders.

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✅ Fix: Force NVENC into a Mac-compatible profile + level

For H.264 (best compatibility):

ffmpeg -i input.mp4 \
-r 30 -c:v h264_nvenc -b:v 60M -maxrate 70M -bufsize 140M \
-preset p7 -profile:v high -level:v 5.1 -pix_fmt yuv420p \
-c:a aac -b:a 320k output.mp4

• -profile:v high → QuickTime prefers high (not main10, not baseline).
• -level:v 5.1 → supports 4K+ resolutions at high bitrates.
• -pix_fmt yuv420p → Apple won’t play 4:2:2 or 4:4:4, only 4:2:0.
• -c:a aac -b:a 320k → CoreAudio won’t accept some exotic audio codecs, so AAC is safest.

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For HEVC (H.265), use:

ffmpeg -i input.mp4 \
-r 30 -c:v hevc_nvenc -b:v 60M -maxrate 70M -bufsize 140M \
-preset p7 -profile:v main -level:v 5.1 -pix_fmt yuv420p \
-c:a aac -b:a 320k output.mp4

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🔍 Why your previous file failed on macOS

1. Pixel format — NVENC defaults to yuv444p or yuv420p10le if the source is >8-bit. Apple’s decoders choke on that.
2. Audio codec — If you left audio as copy, it might be PCM, MP3, or DTS, which QuickTime won’t play inside MP4.
3. Profile/Level — QuickTime enforces H.264/H.265 profile-level compliance strictly.

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👉 Question: do you need Apple’s QuickTime/iOS compatibility, or is playback on VLC/Kodi fine?
If it must play natively in macOS/iOS, I can tighten the command to 100% QuickTime-safe settings (like -movflags +faststart). Would you like me to draft that?

You

it didnt even open on VLC on mac

ChatGPT

Ah, thanks — if even VLC on macOS won’t open it, that usually means the MP4 itself was muxed incorrectly, not just a QuickTime compatibility thing.
This can happen with NVENC when FFmpeg doesn’t force a standard pixel format / container layout. Let’s make the output bullet-proof.

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Try this command (H.264, safest for macOS + VLC):

ffmpeg -i input.mp4 \
-r 30 -c:v h264_nvenc -b:v 60M -maxrate 70M -bufsize 140M \
-preset p7 -profile:v high -level:v 5.1 -pix_fmt yuv420p \
-c:a aac -b:a 320k -movflags +faststart output.mp4

Key fixes added:

• -pix_fmt yuv420p → forces 8-bit 4:2:0 (universally supported).
• -c:a aac → AAC audio (guaranteed support inside MP4).
• -movflags +faststart → rearranges MP4 metadata so players can open/stream it properly.
• -profile:v high -level:v 5.1 → ensures a valid H.264 stream for 4K+.

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If you want HEVC (H.265):

ffmpeg -i input.mp4 \
-r 30 -c:v hevc_nvenc -b:v 60M -maxrate 70M -bufsize 140M \
-preset p7 -profile:v main -level:v 5.1 -pix_fmt yuv420p \
-c:a aac -b:a 320k -movflags +faststart output.mp4

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⚠️ If this still fails on VLC, it might mean your GPU/NVENC build produced a non-standard stream. In that case, the fallback is to encode with software libx264, which is slower but guaranteed compatible:

ffmpeg -i input.mp4 \
-r 30 -c:v libx264 -b:v 60M -maxrate 70M -bufsize 140M \
-preset veryslow -profile:v high -level:v 5.1 -pix_fmt yuv420p \
-c:a aac -b:a 320k -movflags +faststart output.mp4

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👉 Do you want me to tune this for maximum compatibility on Mac/iOS (QuickTime, Safari, iPhone, iPad), or just make sure VLC plays it everywhere?

You

why not use the hwaccel?

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ChatGPT

Totally fair to want HW accel. You can still use it—just use it safely so the output stays Mac-friendly.

Why your earlier HW run went sideways:

• NVDEC (CUDA decode) can fail on some H.264 streams (too many decode surfaces, odd profiles), which then cascades into a bad transcode.
• NVENC defaults may emit formats Apple won’t open (e.g., 10-bit or 4:4:4, wrong level/profile, odd VBV).
• If audio stays as a weird codec inside MP4, QuickTime chokes.

Below are three solid options. All hit ~60 Mb/s and produce files that open in QuickTime and VLC on macOS.

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1) Most robust (CPU decode + NVENC encode)

You still get GPU-fast encoding, skip the fragile CUDA decode, and force Apple-safe settings.

ffmpeg -i input.mp4 \
-r 30 -c:v h264_nvenc -rc vbr_hq -b:v 60M -maxrate 70M -bufsize 140M \
-preset p7 -tune hq -spatial_aq 1 -aq-strength 8 \
-profile:v high -level:v 5.1 -pix_fmt yuv420p -g 60 -bf 3 -rc-lookahead 32 \
-c:a aac -b:a 320k -movflags +faststart output.mp4

Why this works: Apple-safe 8-bit 4:2:0, explicit profile/level for 4096×4096@30, MP4 faststart, and a high-quality NVENC rate control (vbr_hq + AQ).

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2) Full-GPU path (CUDA decode + NVENC encode)

Use this if you really want GPU-to-GPU. We keep the frames on GPU, but tame NVDEC.

ffmpeg -hwaccel cuda -hwaccel_output_format cuda -threads 1 -extra_hw_frames 8 \
-i input.mp4 \
-r 30 -c:v h264_nvenc -rc vbr_hq -b:v 60M -maxrate 70M -bufsize 140M \
-preset p7 -tune hq -spatial_aq 1 -aq-strength 8 \
-profile:v high -level:v 5.1 -pix_fmt yuv420p -g 60 -bf 3 -rc-lookahead 32 \
-c:a aac -b:a 320k -movflags +faststart output.mp4

If you still see NVDEC errors, fall back to Option 1 (CPU decode).

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3) If you prefer HEVC (smaller files at same bitrate)

Swap the encoder; still Mac-compatible:

ffmpeg -i input.mp4 \
-r 30 -c:v hevc_nvenc -rc vbr_hq -b:v 60M -maxrate 70M -bufsize 140M \
-preset p7 -tune hq -spatial_aq 1 -aq-strength 8 \
-profile:v main -level:v 5.1 -pix_fmt yuv420p -g 60 -bf 4 -rc-lookahead 32 \
-c:a aac -b:a 320k -movflags +faststart output.mp4

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Quick sanity checks (optional but helpful)

• Inspect output: ffprobe -hide_banner -select_streams v:0 -show_streams output.mp4
  Verify pix_fmt=yuv420p, profile=High (H.264) or Main (HEVC), level=5.1, and avg_frame_rate=30/1.
• If QuickTime still won’t open it, try forcing a stricter level or lower refs/B-frames: add -refs 4 -bf 2 -g 60.

This way you do use HW accel, but with guardrails so the file plays everywhere on macOS.

You

what is all this crap and why do we specify it?

-tune hq -spatial_aq 1 -aq-strength 8 -profile:v high -level:v 5.1 -pix_fmt yuv420p -g 60 -bf 3 -rc-lookahead 32

ChatGPT

Good question — it looks like a wall of knobs, but each of those flags exists to deal with quirks of NVENC and Apple’s picky playback stack.
Here’s what each does, and why it mattered in the examples I gave you:

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🎛 Quality / rate control tuning

• -tune hq → tells NVENC to favor quality over speed.
• -spatial_aq 1 -aq-strength 8 → enables “adaptive quantization,” which adjusts bitrate within each frame so flat areas don’t waste bits and detailed areas keep sharp. Without this, NVENC at a fixed bitrate can look blocky.

📺 Compatibility with macOS

• -profile:v high → locks the H.264 stream to the High profile, which QuickTime/iOS/macOS require for high-res content. (If NVENC defaults to something exotic, Apple refuses to play it.)
• -level:v 5.1 → declares playback capability for 4K+ at 30fps and high bitrate. If this is missing or too low, Apple won’t open the file.
• -pix_fmt yuv420p → forces 8-bit 4:2:0 pixel format, the only one universally supported. NVENC may emit 10-bit (yuv420p10le) or 4:4:4 if not forced — those break QuickTime.

🔄 Frame control

• -g 60 → sets GOP size = 60 frames (~2 seconds at 30fps). Many Apple players expect GOP ≤ 2s. Longer GOPs can cause stutter or no playback.
• -bf 3 → allows 3 B-frames between reference frames, which improves compression. Apple is fine with this, but it must be defined.
• -rc-lookahead 32 → lets NVENC look ahead up to 32 frames for smarter bitrate distribution (improves quality at same bitrate).

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📝 TL;DR

• Some flags (profile, level, pix_fmt, g) are about compatibility with Apple’s decoders.
• Some (aq, lookahead, bf) are about squeezing quality out of NVENC at your chosen bitrate.
• Without them, NVENC will happily spit out a stream that VLC plays, but QuickTime/iOS might refuse — or you’ll get “muddy” quality at 60 Mb/s.

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👉 Do you want me to strip this down to the minimal command that just ensures Apple-compatibility (no extra quality knobs), so it’s easier to read?

You

throws an error about presets p1-p7

ChatGPT

Ah — I see what’s happening.
The p1–p7 presets are part of the newer NVIDIA SDK (FFmpeg ≥ 5.0 with recent drivers). If your build of FFmpeg doesn’t have the new API, those flags won’t work — you’ll get an error.

On older builds, NVENC uses the classic preset names like:

• -preset default
• -preset slow
• -preset medium
• -preset fast

So instead of:

-preset p7

use:

-preset slow

or

-preset default

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✅ Fixed command (H.264 NVENC, Mac-friendly, older FFmpeg builds):

ffmpeg -i input.mp4 \
-r 30 -c:v h264_nvenc -b:v 60M -maxrate 70M -bufsize 140M \
-preset slow -profile:v high -level:v 5.1 -pix_fmt yuv420p \
-c:a aac -b:a 320k -movflags +faststart output.mp4

Notes

• If you want smaller files, swap h264_nvenc → hevc_nvenc.
• If Apple playback is still flaky, add -g 60 -bf 2 to keep the GOP structure conservative.

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👉 Do you want me to give you one “minimal safe command” that just works everywhere on macOS/iOS (no quality tweaks), or a high-quality tuned version for your setup?

You

InitializeEncoder failed: invalid param (8): Presets P1 to P7 are not supported with older 2 Pass RC Modes(CBR_HQ, VBR_HQ) and cbr lowdelay. Enable NV_ENC_RC_PARAMS::multiPass flag for two pass encoding a [vost#0:0/h264_nvenc @ 00000178aa0cbdc0] Error initializing output stream: Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

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You hit an NVENC rate-control/preset mismatch.

That error means your FFmpeg/NVENC combo doesn’t support the “HQ 2-pass” modes (vbr_hq/cbr_hq) together with the (new) preset family. Fix it by either:

A) Use standard VBR/CBR (1-pass) — simplest & most compatible

ffmpeg -i input.mp4 \
-r 30 -c:v h264_nvenc -rc vbr -b:v 60M -maxrate 70M -bufsize 140M \
-preset slow -profile:v high -level:v 5.1 -pix_fmt yuv420p -g 60 -bf 2 \
-c:a aac -b:a 320k -movflags +faststart output.mp4

• Drops vbr_hq/cbr_hq entirely → avoids the “InitializeEncoder failed” error.
• Keeps your 50–70 Mb/s target and stays Mac-friendly.

B) If you really want the HQ 2-pass modes

Enable NVENC’s multipass explicitly (supported on newer drivers/FFmpeg):

ffmpeg -i input.mp4 \
-r 30 -c:v h264_nvenc -rc vbr_hq -multipass fullres \
-b:v 60M -maxrate 70M -bufsize 140M \
-preset slow -profile:v high -level:v 5.1 -pix_fmt yuv420p -g 60 -bf 2 \
-c:a aac -b:a 320k -movflags +faststart output.mp4

If fullres errors, try -multipass qres. If your build still complains, fall back to Option A.

Why this happened

• vbr_hq/cbr_hq = 2-pass modes. Older NVENC/FFmpeg combos need -multipass set; some don’t support HQ with the newer P1–P7 presets at all.
• Using classic presets like -preset slow avoids the P1–P7 issue.

Extra sanity checks (if it still fails)

• Remove CUDA decoding (some inputs break NVDEC): just omit -hwaccel cuda.
• Confirm compatibility: ffprobe -hide_banner -select_streams v:0 -show_streams output.mp4 and look for pix_fmt=yuv420p, profile=High, level=5.1, avg_frame_rate=30/1.
• If your GPU is older and balks at 4096×4096, switch to HEVC (often more forgiving):

  -c:v hevc_nvenc -rc vbr -b:v 60M -maxrate 70M -bufsize 140M -profile:v main -level:v 5.1 -pix_fmt yuv420p

Try Option A first—it’s the most reliable across older NVENC stacks and macOS players.

You

invalid level 8

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[Unsupported Content]

You

invalid param (8) invalid level

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ChatGPT

[Unsupported Content]

ChatGPT

That message is a bit misleading. The “(8)” you see is NVENC’s error code for invalid parameter — it’s not a level value. You likely passed an unsupported level (e.g., -level 8) or your build expects a different level format.

What to do

• Easiest: don’t set the level at all and let NVENC pick it (-level:v omitted).
• If you do set it: use a valid level for your resolution/fps. For 4096×4096 @ 30 fps:
  • H.264: -level:v 5.1 (some builds want -level:v 51)
  • HEVC: -level:v 5.1 (or omit)

Clean, compatible commands (no level specified)

H.264 (NVENC), ~60 Mb/s, Mac-friendly

ffmpeg -i input.mp4 -r 30 \
-c:v h264_nvenc -rc vbr -b:v 60M -maxrate 70M -bufsize 140M \
-preset slow -profile:v high -pix_fmt yuv420p -g 60 -bf 2 \
-c:a aac -b:a 320k -movflags +faststart output.mp4

HEVC (NVENC), ~60 Mb/s

ffmpeg -i input.mp4 -r 30 \
-c:v hevc_nvenc -rc vbr -b:v 60M -maxrate 70M -bufsize 140M \
-preset slow -profile:v main -pix_fmt yuv420p -g 60 -bf 3 \
-c:a aac -b:a 320k -movflags +faststart output.mp4

If you really want to pin the level, add -level:v 5.1 (or 51 for some H.264 NVENC builds) to the above. Avoid -level 8 — that’s invalid and triggers the same “(8) invalid param” error.

If you still get a level error even with 5.1, just omit -level:v and let NVENC set a suitable one automatically.

You

let’s start FROM SCRATCH. Minimal ffmpeg command that uses cuda and is maximally compatible. audio is copied, and framerate is maintained between 50-70

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Here’s a from-scratch, minimal, Mac-compatible command that uses NVIDIA NVENC (CUDA) to encode, keeps the source framerate (e.g., 60 fps), copies audio, and targets ~50–70 Mb/s:

ffmpeg -i input.mp4 \
-c:v h264_nvenc -rc vbr -b:v 60M -maxrate 70M -bufsize 140M \
-pix_fmt yuv420p -profile:v high \
-c:a copy -movflags +faststart output.mp4

Why this is “minimal & compatible”:

• No -r → framerate is preserved (e.g., stays 60 fps, which is within 50–70).
• h264_nvenc → CUDA hardware encode (fast).
• -b:v 60M -maxrate 70M -bufsize 140M → average ~60 Mb/s, cap ~70 Mb/s.
• -pix_fmt yuv420p -profile:v high → plays cleanly on macOS/iOS/QuickTime and VLC.
• -c:a copy → audio untouched.
• -movflags +faststart → better MP4 compatibility/instant open.

If you specifically want CUDA decoding too (full GPU path), add these two flags at the front; if it errors on your setup, just remove them and use the command above:

-hwaccel cuda -hwaccel_output_format cuda

So, full-GPU variant:

ffmpeg -hwaccel cuda -hwaccel_output_format cuda -i input.mp4 \
-c:v h264_nvenc -rc vbr -b:v 60M -maxrate 70M -bufsize 140M \
-pix_fmt yuv420p -profile:v high \
-c:a copy -movflags +faststart output.mp4

You

the bitrate nmust be between 50-70. the framerate should be 30

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ChatGPT

Here’s a minimal, CUDA-encode (NVENC), Mac-compatible command that forces 30 fps, copies audio, and keeps video between 50–70 Mb/s:

ffmpeg -i input.mp4 -r 30 \
-c:v h264_nvenc -rc vbr -b:v 60M -minrate 50M -maxrate 70M -bufsize 140M \
-pix_fmt yuv420p -profile:v high \
-c:a copy -movflags +faststart output.mp4

• -r 30 → output framerate 30 fps
• h264_nvenc → NVIDIA GPU encoder (CUDA)
• -b:v 60M -minrate 50M -maxrate 70M -bufsize 140M → target ~60 Mb/s within 50–70 cap
• -pix_fmt yuv420p -profile:v high → plays cleanly on macOS/iOS/QuickTime
• -c:a copy → audio untouched (⚠ if the source audio isn’t MP4-friendly, QuickTime may not play; switch to -c:a aac if needed)
• -movflags +faststart → better MP4 compatibility

If you also want GPU decoding, prepend -hwaccel cuda -hwaccel_output_format cuda — but leave it out if your system’s NVDEC has issues.