How to double the frame rate by deinterlacing in bob mode
- Step 1Confirm the source is interlaced — Bob mode only makes sense on interlaced footage (it promotes fields to frames). A
25i/29.97i/50ilabel or combing on a paused motion frame confirms it. On a progressive source there are no separate fields to double. - Step 2Drop the clip onto the deinterlacer — MP4, MOV, MKV, WEBM, AVI, M4V, and TS are accepted. The file loads into the browser FFmpeg engine; nothing uploads.
- Step 3Switch Mode to 0 (double fps) — Change the Mode selector from the default
1to0. This runsyadif=0(bob), which outputs one frame per field — doubling the frame rate. The UI label confirms0 = double fps. - Step 4Expect a larger output and a longer encode — Twice the frames means roughly twice the encoding work and a larger MP4. The duration is unchanged — only the frame count and rate double. Plan for a longer WASM processing time on HD sources.
- Step 5Run the bob deinterlace — JAD runs
yadif=0, re-encodes the doubled-frame video to H.264 CRF 20 preset medium, and copies the audio so it stays in sync. - Step 6Download and check motion smoothness — Play the MP4 on a high-refresh display — motion should be noticeably smoother than the source. Confirm the frame rate (e.g. 50p) in your player's stats or media info.
Bob-mode frame-rate doubling
Mode 0 promotes each field to a frame, so output rate is exactly double the source rate.
| Source | Fields/sec | Mode 0 output | Frame count vs. source |
|---|---|---|---|
| 25i | 50 | 50p | 2× |
| 29.97i | 59.94 | 59.94p | 2× |
| 50i (rare) | 100 | 100p | 2× |
| 24i / telecined | varies | judgey — use Mode 1 instead | n/a |
Mode 0 (bob) vs Mode 1 (single-rate)
Both are yadif; the difference is whether each field becomes its own frame.
| Aspect | Mode 0 (bob) | Mode 1 (default) |
|---|---|---|
| Filter | yadif=0 | yadif=1 |
| Frames out | One per field (2×) | One per source frame |
| Frame rate | Doubled | Unchanged |
| Motion | Smoothest | Original cadence |
| File size | Larger | Smaller |
| Best for | Sports, action, live | Film, drama, archive |
Tier limits (output is larger in bob mode)
Because bob mode doubles the frame count, output files are bigger — but the cap is on input size, not output.
| Tier | Max input file size | Batch files |
|---|---|---|
| Free | 1 GB | 1 |
| Pro | 10 GB | 5 |
| Pro-media | 100 GB | 50 |
| Developer | 100 GB | Unlimited |
Cookbook
Bob-mode recipes that double the frame rate from interlaced sources, with the exact yadif=0 call.
25i sports clip to smooth 50p
A PAL 25i sports capture where smoother motion is the goal. Mode 0 promotes each of the 50 fields per second to a frame.
Input: match.ts, 25i (50 fields/sec) Mode: 0 (double fps / bob) Filter: -vf yadif=0 Output: match.mp4, 50p, smoother motion, ~2× frames, larger file
29.97i action footage to 59.94p
An NTSC 29.97i action clip. Mode 0 yields 59.94p for high-frame-rate playback.
Input: action.mkv, 29.97i Mode: 0 Output: action.mp4, 59.94p Duration unchanged; frame count doubled
Compare bob vs single-rate on the same clip
Run the same source twice to feel the difference: Mode 1 keeps cadence, Mode 0 smooths motion.
Run A (Mode 1): -vf yadif=1 → 25p, original cadence Run B (Mode 0): -vf yadif=0 → 50p, smoother, bigger file Pick the one that looks right for your content.
Audio stays in sync at double rate
Even though the video frame count doubles, audio is stream-copied and remains in sync because the duration is unchanged.
Input: live.mov, 25i, AAC audio Mode: 0 Video: 50p (doubled frames) Audio: AAC copied, same duration, in sync Output: live.mp4
Bob then upload to YouTube as HFR
YouTube plays 50/60p natively, so a bob-mode export gives smooth high-frame-rate playback online.
Step 1: deinterlacer Mode 0 → 50p MP4 Step 2: upload to YouTube (plays at 50p natively) See also: /video-tools/solutions/fix-interlaced-tv-footage-for-youtube
Edge cases and what actually happens
Output file is much larger
ExpectedBob mode doubles the frame count, so the encoded MP4 is correspondingly larger and takes about twice as long to encode. This is inherent to double-rate deinterlacing. If size matters more than smoothness, use Mode 1 instead.
Source is already progressive
AvoidBob promotes fields to frames, but a progressive source has no separate fields. Running Mode 0 on progressive footage just interpolates and softens at a doubled rate with no real benefit. Use it only on interlaced sources.
Telecined film fed into bob mode
LimitedFilm telecined to 29.97i doesn't have 60 genuine moments per second; bob mode will produce 59.94p but motion can look odd. For telecined film prefer Mode 1, or inverse telecine (not offered here).
Downstream tool expects the original frame rate
MismatchIf a later step (an NLE sequence, a delivery spec) expects 25p/29.97p, a 50p/59.94p bob output won't match and may get re-conformed. Use Mode 1 to keep the original rate when the target is single-rate.
Output is always MP4
By designBob mode still re-encodes to H.264 MP4 regardless of input container. Re-encode to another container afterwards with the transcoder if needed.
Large HD source over the tier cap
RejectedThe cap is on input size: Free 1 GB, Pro 10 GB, Pro-media/Developer 100 GB. A long HD source can exceed the free cap before bob even runs. Split or upgrade.
Doubled rate doesn't look smoother on a 30 Hz display
Display-limitedA 50p/59.94p file only shows its smoothness on a display that can refresh that fast. On a 30 Hz output the player drops frames and the benefit is lost. Check on a 50/60 Hz+ display.
Slow encode on long HD clips
ExpectedTwice the frames plus FFmpeg.wasm (CPU-bound, no hardware acceleration for yadif) makes bob mode the slowest deinterlace path. Trim to the needed range first with the lossless trimmer.
Frequently asked questions
What does bob deinterlacing actually do?
It promotes each field to its own full frame instead of merging field pairs. Since interlaced video has two fields per frame (each from a slightly different moment), this doubles the frame rate: 25i → 50p, 29.97i → 59.94p. The extra frames come from the temporal information that was already in the source.
How do I enable bob mode?
Set the Mode selector to 0 (the UI labels it '0 = double fps'). That runs yadif=0. The default is Mode 1, which keeps the original frame rate.
Why is the output file so much bigger?
Bob mode doubles the frame count, so there are twice as many frames to encode — the MP4 is correspondingly larger and the encode takes about twice as long. The duration is unchanged; only the frame rate and count double.
Is bob mode better than single-rate deinterlacing?
For motion smoothness on sports, action, and live content, yes — it keeps every field's moment as a displayed frame. For film, drama, or archive where you want the original cadence (and a smaller file), single-rate Mode 1 is better.
Will the audio stay in sync at double rate?
Yes. Audio is stream-copied and the clip duration is unchanged, so it stays perfectly in sync with the doubled-frame video.
Can YouTube play the doubled frame rate?
Yes. YouTube plays 50p and 59.94p natively. A bob-mode export gives smooth high-frame-rate playback online — see the YouTube prep guide.
Should I use bob mode on film?
Usually not. Film doesn't have 50/60 genuine moments per second, so bob can make telecined or film-sourced content look odd. Use Mode 1 to keep the cadence, or inverse telecine for true film recovery (not offered in this tool).
Does it work on progressive video?
There's no benefit. Progressive footage has no separate fields to promote, so bob mode just interpolates and softens at a doubled rate. Only use it on interlaced sources.
What's the output codec and container?
H.264 video in an MP4 container at CRF 20, preset medium — same as the other deinterlace modes. Only the frame rate differs. Use the transcoder if you need a different codec.
Why doesn't the doubled rate look smoother on my screen?
Your display has to refresh at 50/60 Hz+ to show 50p/59.94p smoothness. On a 30 Hz output the player drops frames and the benefit disappears. Check the file on a high-refresh display.
How big can my input be?
The size cap is on the input: Free 1 GB, Pro 10 GB, Pro-media and Developer 100 GB. There's no duration limit. The larger bob output doesn't count against the cap, but it does take longer to encode.
Why is bob mode slower than Mode 1?
It produces twice the frames, and yadif + libx264 run on FFmpeg.wasm (CPU-bound — no hardware acceleration for this filter). Trim to just the segment you need first with the lossless trimmer to cut processing time.
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