Migration API FFmpeg 6.0+ (codecpar/AVBSFContext) : tested for compatibility FFmpeg 8.0/8.1 (PR v2)

[M2G]

Background

The segment package was still using the old FFmpeg 2.x API (AVStream->codec,
AVBitStreamFilterContext, av_register_all(), av_free_packet()...), which was deprecated and then
removed in recent versions of FFmpeg.
This fork migrates the code to the modern API, which has been stable since FFmpeg 6.0 and has been verified as compatible up to FFmpeg 8.

Changes

AVStream->codec to AVStream->codecpar: Copy parameters using
avcodec_parameters_copy() instead of manually setting each field (codec_type, bit_rate,
extradata, channel_layout, etc.)

• AVBitStreamFilterContext to AVBSFContext: Replaces
  av_bitstream_filter_init()/av_bitstream_filter_filter() with
  av_bsf_alloc()/av_bsf_init()/av_bsf_send_packet()/av_bsf_receive_packet()
• AVPacket on the stack to av_packet_alloc()/av_packet_free(): Replaces the old
  av_free_packet() (removed since FFmpeg 4.0)
• avformat_alloc_context() + av_guess_format() to avformat_alloc_output_context2()
• Removal of av_register_all() (no-op since FFmpeg 4.0)
• Removal of CODEC_FLAG_GLOBAL_HEADER and the CODEC_ID_MP3/CODEC_ID_AC3 switch
  (automatically handled by avcodec_parameters_copy)
• Build system: Hard-coded #cgo LDFLAGS/CFLAGS (path /root/ffmpeg_build) replaced
  with #cgo pkg-config: libavformat libavcodec libavutil, for a portable build without
  path changes across environments
• Cleaned up a dead variable (first_frame_sec, assigned but never read)

Tests performed

• OK : Clean compilation (gcc -Wall -Wextra, 0 warnings) against FFmpeg 8.0 compiled from
  source (libavcodec 62 / libavformat 62)
• OK : Successful compilation on macOS (Apple Silicon) via Homebrew, FFmpeg 8.1.2, pkg-config
• OK : End-to-end HLS segmentation working: 12-second H.264/AAC MP4 input split into 3
  4-second .ts segments + valid .m3u8 playlist; each segment validated with ffprobe

Compatibility

Linux and macOS (Apple Silicon), FFmpeg 6.0 through 8.1, without platform-specific code
thanks to pkg-config.