How to Convert M2TS to MP4 Without Quality Loss

What Are M2TS Files and Why Convert Them?

M2TS stands for MPEG-2 Transport Stream, a container format used primarily for Blu-ray discs, AVCHD camcorders, and HDTV recordings. If you have ever ripped a Blu-ray disc or recorded live television with a capture card, you have likely encountered .m2ts files sitting inside a BDMV/STREAM folder.

The problem with M2TS is compatibility. While the format excels at storing high-definition H.264 or H.265 video with lossless audio tracks (DTS-HD, TrueHD), almost no web browser, smartphone, or streaming platform can play M2TS files directly. Converting to MP4 solves this by repackaging the same video and audio streams into a universally supported container. In many cases, this conversion requires zero re-encoding, meaning you lose absolutely nothing in the process.

This guide covers three methods: lossless remuxing with FFmpeg, full re-encoding for incompatible codecs, and a quick online conversion option. We will also address common M2TS-specific issues like handling multiple audio tracks and dealing with Blu-ray folder structures.

Understanding the M2TS Container

Before converting, it helps to understand what is inside an M2TS file. The container typically holds:

M2TS files use 192-byte transport stream packets (compared to the standard 188 bytes in regular .ts files). The extra 4 bytes contain a timestamp used for Blu-ray disc seek operations. This is the key structural difference between .m2ts and .ts files, and FFmpeg handles both transparently.

Method 1: Lossless Remux (No Quality Loss)

If your M2TS file contains H.264 or H.265 video, you can copy the streams directly into an MP4 container without any quality degradation. This process takes seconds regardless of file size.

Basic Remux

ffmpeg -i input.m2ts -c copy -movflags +faststart output.mp4

The -c copy flag tells FFmpeg to copy all streams as-is. The -movflags +faststart flag moves the MP4 metadata to the beginning of the file, enabling progressive playback in web browsers.

Remux with Audio Conversion

M2TS files from Blu-ray discs often contain DTS-HD Master Audio or Dolby TrueHD, which most MP4 players cannot decode. Convert the audio while preserving the video:

ffmpeg -i input.m2ts -c:v copy -c:a aac -b:a 256k \
  -movflags +faststart output.mp4

Select a Specific Audio Track

Blu-ray M2TS files frequently contain multiple audio tracks (English 7.1, English commentary, foreign language dub). Pick the one you want:

# List all audio tracks first
ffprobe -v error -select_streams a -show_entries \
  stream=index,codec_name,channels -of table input.m2ts

# Keep only the first audio track
ffmpeg -i input.m2ts -map 0:v:0 -map 0:a:0 -c copy output.mp4

Method 2: Full Re-encode

If the M2TS contains MPEG-2 video (common in HDTV recordings and older Blu-ray discs), you need to re-encode:

ffmpeg -i input.m2ts -c:v libx264 -crf 18 -preset slow \
  -c:a aac -b:a 192k -movflags +faststart output.mp4

For MPEG-2 source material, a CRF of 18 preserves virtually all visible detail. The slow preset gives better compression efficiency at the cost of longer encoding time.

Handling Interlaced Content

HDTV recordings are often interlaced (1080i). Deinterlace during conversion for clean progressive output:

ffmpeg -i input.m2ts -vf "yadif=mode=0" \
  -c:v libx264 -crf 18 -preset slow \
  -c:a aac -b:a 192k output.mp4

The yadif filter with mode=0 outputs one frame per field, which produces smooth motion from interlaced sources.

Method 3: Online Conversion

For a quick conversion without installing any software, use the M2TS to MP4 converter online. Upload your M2TS file, and the tool automatically detects the codecs inside and chooses the optimal conversion path. For more video format options, try the full Video Converter.

Handling Blu-ray Folder Structures

Blu-ray rips typically organize M2TS files in a specific folder structure:

BDMV/
  STREAM/
    00000.m2ts   (main feature)
    00001.m2ts   (bonus feature)
    00002.m2ts   (trailer)
  PLAYLIST/
    00000.mpls   (playlist referencing streams)

The main feature is usually the largest .m2ts file in the STREAM folder. To convert all M2TS files in a directory:

mkdir -p converted
for file in BDMV/STREAM/*.m2ts; do
  ffmpeg -i "$file" -c:v copy -c:a aac -b:a 192k \
    -movflags +faststart "converted/$(basename "${file%.m2ts}.mp4")"
done

For more batch processing techniques, see our batch processing guide.

Quality and Settings Tips

Video CRF values depend on the source quality and your tolerance for file size:

Audio bitrate for AAC when converting from lossless Blu-ray audio: use 256 kbps for 5.1 surround content and 192 kbps for stereo. Below 128 kbps, you will start to hear compression artifacts. For more on audio quality, read our audio bitrate guide.

Subtitle handling: M2TS files from Blu-ray discs use PGS (Presentation Graphic Stream) subtitles, which are bitmap-based images — not text. MP4 does not support PGS. Your options are to burn them into the video (-vf "subtitles=input.m2ts:si=0") or to OCR them into SRT text files using a tool like SubtitleEdit.

Common Issues and Troubleshooting

"Discarding non-monotone timestamps" warnings

M2TS files from HDTV recordings often have timestamp discontinuities from commercial breaks or channel switching. FFmpeg usually handles these automatically, but if the output has sync issues:

ffmpeg -fflags +genpts -i input.m2ts -c copy output.mp4

The -fflags +genpts flag regenerates presentation timestamps.

Huge file size after re-encoding

If the output MP4 is larger than the source M2TS, you are likely using a CRF that is too low for the source quality. HDTV recordings are already compressed at moderate bitrates (15-20 Mbps). A CRF of 20-22 will match the source quality without inflating the file. For tips on keeping file sizes down, see our guide on how to reduce video file size.

Audio sync drift over long recordings

Some HDTV M2TS recordings develop audio drift over several hours. Fix this with:

ffmpeg -i input.m2ts -c:v copy -c:a aac -b:a 192k \
  -af "aresample=async=1" output.mp4

Black frames at the beginning

Blu-ray M2TS files sometimes have a few seconds of black at the start (disc menu transition). Trim them:

ffmpeg -ss 3 -i input.m2ts -c copy -movflags +faststart output.mp4

Conclusion

Converting M2TS to MP4 is straightforward once you identify the codecs inside. For Blu-ray rips with H.264 video, a lossless remux takes seconds and preserves perfect quality. For HDTV recordings with MPEG-2 video, re-encoding to H.264 with a CRF of 18-22 gives you excellent quality in a fraction of the original file size.

Ready to convert? Try our free M2TS to MP4 converter — no registration required.