群晖NAS上FFmpeg无法将.ts转成.mp4的问题求助

问题背景 #

在群晖NAS上使用FFmpeg将DVR录制的.ts格式视频转换为.mp4，执行命令后失败，具体命令及输出如下：

$ ffmpeg -analyzeduration 2147483647 -probesize 2147483647 -i 'video.ts' -acodec -vcodec copy 'video.mp4'

输出信息：

ffmpeg version 4.1.8 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 8.5.0 (GCC)
  configuration: --prefix=/usr --incdir='${prefix}/include/ffmpeg' --arch=i686 --target-os=linux --cross-prefix=/usr/local/x86_64-pc-linux-gnu/bin/x86_64-pc-linux-gnu- --enable-cross-compile --enable-optimizations --enable-pic --enable-gpl --enable-shared --disable-static --disable-stripping --enable-version3 --enable-encoders --enable-pthreads --disable-protocols --disable-protocol=rtp --enable-protocol=file --enable-protocol=pipe --disable-muxer=image2 --disable-muxer=image2pipe --disable-swscale-alpha --disable-ffplay --disable-ffprobe --disable-doc --disable-devices --disable-bzlib --disable-altivec --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libmp3lame --disable-vaapi --disable-cuvid --disable-nvenc --disable-decoder=aac --disable-decoder=aac_fixed --disable-encoder=aac --disable-decoder=amrnb --disable-decoder=ac3 --disable-decoder=ac3_fixed --disable-encoder=zmbv --disable-encoder=dca --disable-decoder=dca --disable-encoder=ac3 --disable-encoder=ac3_fixed --disable-encoder=eac3 --disable-decoder=eac3 --disable-encoder=truehd --disable-decoder=truehd --disable-encoder=hevc_vaapi --disable-decoder=hevc --disable-muxer=hevc --disable-demuxer=hevc --disable-parser=hevc --disable-bsf=hevc_mp4toannexb --x86asmexe=yasm --cc=/usr/local/x86_64-pc-linux-gnu/bin/x86_64-pc-linux-gnu-wrap-gcc --enable-yasm --enable-libx264 --enable-encoder=libx264
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
[mpegts @ 0x5591c4feb4c0] Could not find codec parameters for stream 1 (Audio: aac ([15][0][0][0] / 0x000F), 0 channels, 199 kb/s): unspecified sample rate
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, mpegts, from 'video.ts':
  Duration: 02:01:58.77, start: 1.405122, bitrate: 4094 kb/s
  Program 1 
    Metadata:
      service_name    : Service01
      service_provider: FFmpeg
    Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], Closed Captions, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
    Stream #0:1[0x101]: Audio: aac ([15][0][0][0] / 0x000F), 0 channels, 199 kb/s
[NULL @ 0x5591c6034980] Unable to find a suitable output format for 'copy'
copy: Invalid argument

通过VLC查看，该.ts文件的音频为AAC格式，当前使用的FFmpeg（来自SynoCommunity）支持的音频编码器列表如下：

A..... adpcm_adx            SEGA CRI ADX ADPCM
 A..... g722                 G.722 ADPCM (codec adpcm_g722)
 A..... g726                 G.726 ADPCM (codec adpcm_g726)
 A..... g726le               G.726 little endian ADPCM ("right-justified") (codec adpcm_g726le)
 A..... adpcm_ima_qt         ADPCM IMA QuickTime
 A..... adpcm_ima_wav        ADPCM IMA WAV
 A..... adpcm_ms             ADPCM Microsoft
 A..... adpcm_swf            ADPCM Shockwave Flash
 A..... adpcm_yamaha         ADPCM Yamaha
 A..... alac                 ALAC (Apple Lossless Audio Codec)
 A..... libopencore_amrnb    OpenCORE AMR-NB (Adaptive Multi-Rate Narrow-Band) (codec amr_nb)
 A..... aptx                 aptX (Audio Processing Technology for Bluetooth)
 A..... aptx_hd              aptX HD (Audio Processing Technology for Bluetooth)
 A..... comfortnoise         RFC 3389 comfort noise generator
 A..... flac                 FLAC (Free Lossless Audio Codec)
 A..... g723_1               G.723.1
 A..X.. mlp                  MLP (Meridian Lossless Packing)
 A..... mp2                  MP2 (MPEG audio layer 2)
 A..... mp2fixed             MP2 fixed point (MPEG audio layer 2) (codec mp2)
 A..... libmp3lame           libmp3lame MP3 (MPEG audio layer 3) (codec mp3)
 A..... nellymoser           Nellymoser Asao
 A..X.. opus                 Opus
 A..... pcm_alaw             PCM A-law / G.711 A-law
 A..... pcm_f32be            PCM 32-bit floating point big-endian
 A..... pcm_f32le            PCM 32-bit floating point little-endian
 A..... pcm_f64be            PCM 64-bit floating point big-endian
 A..... pcm_f64le            PCM 64-bit floating point little-endian
 A..... pcm_mulaw            PCM mu-law / G.711 mu-law
 A..... pcm_s16be            PCM signed 16-bit big-endian
 A..... pcm_s16be_planar     PCM signed 16-bit big-endian planar
 A..... pcm_s16le            PCM signed 16-bit little-endian
 A..... pcm_s16le_planar     PCM signed 16-bit little-endian planar
 A..... pcm_s24be            PCM signed 24-bit big-endian
 A..... pcm_s24daud          PCM D-Cinema audio signed 24-bit
 A..... pcm_s24le            PCM signed 24-bit little-endian
 A..... pcm_s24le_planar     PCM signed 24-bit little-endian planar
 A..... pcm_s32be            PCM signed 32-bit big-endian
 A..... pcm_s32le            PCM signed 32-bit little-endian
 A..... pcm_s32le_planar     PCM signed 32-bit little-endian planar
 A..... pcm_s64be            PCM signed 64-bit big-endian
 A..... pcm_s64le            PCM signed 64-bit little-endian
 A..... pcm_s8               PCM signed 8-bit
 A..... pcm_s8_planar        PCM signed 8-bit planar
 A..... pcm_u16be            PCM unsigned 16-bit big-endian
 A..... pcm_u16le            PCM unsigned 16-bit little-endian
 A..... pcm_u24be            PCM unsigned 24-bit big-endian
 A..... pcm_u24le            PCM unsigned 24-bit little-endian
 A..... pcm_u32be            PCM unsigned 32-bit big-endian
 A..... pcm_u32le            PCM unsigned 32-bit little-endian
 A..... pcm_u8               PCM unsigned 8-bit
 A..... pcm_vidc             PCM Archimedes VIDC
 A..... real_144             RealAudio 1.0 (14.4K) (codec ra_144)
 A..... roq_dpcm             id RoQ DPCM
 A..X.. s302m                SMPTE 302M
 A..... sbc                  SBC (low-complexity subband codec)
 A..X.. sonic                Sonic
 A..X.. sonicls              Sonic lossless
 A..... tta                  TTA (True Audio)
 A..X.. vorbis               Vorbis
 A..... wavpack              WavPack
 A..... wmav1                Windows Media Audio 1
 A..... wmav2                Windows Media Audio 2

问题诊断 #

1. 命令语法错误：原命令中-acodec后未指定编码器参数，直接接-vcodec，导致FFmpeg误将-vcodec识别为音频编码器，进而把copy当成输出格式，触发“Unable to find a suitable output format for 'copy'”错误。
2. FFmpeg缺少AAC支持：从FFmpeg的编译配置可以看到，已明确禁用AAC解码器和编码器（--disable-decoder=aac --disable-decoder=aac_fixed --disable-encoder=aac），无法直接解码输入的AAC音频流，也不能通过copy模式复用该音频流到MP4容器。

解决办法 #

1. 转码音频为FFmpeg支持的格式 #

当前FFmpeg支持MP3编码（libmp3lame），可以将音频转码为MP3，视频保持原编码直接拷贝，命令如下：

ffmpeg -analyzeduration 2147483647 -probesize 2147483647 -i 'video.ts' -c:v copy -c:a libmp3lame 'video.mp4'

如需调整音频比特率（比如设置为192kbps），可添加-b:a参数：

ffmpeg -analyzeduration 2147483647 -probesize 2147483647 -i 'video.ts' -c:v copy -c:a libmp3lame -b:a 192k 'video.mp4'

2. 修正命令（仅当FFmpeg支持AAC时可用） #

如果后续更换了支持AAC的FFmpeg版本，可使用以下命令直接拷贝音视频流（无转码，速度更快）：

ffmpeg -analyzeduration 2147483647 -probesize 2147483647 -i 'video.ts' -c copy 'video.mp4'

或者分开指定音视频拷贝：

ffmpeg -analyzeduration 2147483647 -probesize 2147483647 -i 'video.ts' -c:v copy -c:a copy 'video.mp4'

3. 更换支持AAC的FFmpeg版本 #

• 寻找群晖平台上带有AAC支持的FFmpeg第三方包
• 自行编译FFmpeg，编译时移除--disable-decoder=aac等相关禁用参数，添加--enable-aac或--enable-libfdk-aac以开启AAC编码和解码支持

内容的提问来源于stack exchange，提问作者cpo