Several bitstream filters (e.g. dump_extradata, imxdump, mjpeg2jpeg, mjpegadump, mp3decomp, ...) don't buffer packets; instead, they just modify the buffer of one packet and don't change any other of the packet's non-buffer properties. The usual approach of these bitstream filters is to use separate packets for in- and output as follows:
1. Get the input packet via ff_bsf_get_packet() which entails an allocation. 2. Use av_new_packet() to allocate a big enough buffer in the output packet. 3. Perform the actual work of the bitstream filter, i.e. fill the output buffer. 4. Use av_packet_copy_props() to copy the non-buffer fields of the input packet to the output packet. 5. Free the input packet and return. This commit adds two utility functions that allow a different approach: A function to (re)allocate a refcounted buffer with zeroed padding and a function to replace a packet's buffer and the buffer-related fields with information from an AVBufferRef. This allows to modify the bitstream filters as follows: 1. Get the packet via ff_bsf_get_packet_ref(). 2. Use ff_buffer_padded_realloc() to get a big enough refcounted buffer. 3. Perform the actual work of the bitstream filter. 4. Use ff_packet_replace_buffer() to replace the old data in the packet with the modified one and return. The first of these functions is just packet_alloc() from avpacket.c which has been made non-static. Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com> --- An earlier version put the declarations to internal.h, but James suggested putting them into bsf_internal.h (or actually, into bsf.h because bsf_internal.h didn't exist back then), so I went with this. There is currently no user that actually makes use of the reallocation feature; it was initially thought for hevc_mp4toannexb, but then I decided to make it no longer reallocate the output buffer at all any more. But I kept this functionality. Might be useful some day. libavcodec/avpacket.c | 21 ++++++++++++++++----- libavcodec/bsf_internal.h | 27 +++++++++++++++++++++++++++ 2 files changed, 43 insertions(+), 5 deletions(-) diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c index 033f2d8f26..c8f3b0cf7a 100644 --- a/libavcodec/avpacket.c +++ b/libavcodec/avpacket.c @@ -27,6 +27,7 @@ #include "libavutil/mathematics.h" #include "libavutil/mem.h" +#include "bsf_internal.h" #include "bytestream.h" #include "internal.h" #include "packet.h" @@ -69,7 +70,7 @@ void av_packet_free(AVPacket **pkt) av_freep(pkt); } -static int packet_alloc(AVBufferRef **buf, int size) +int ff_buffer_padded_realloc(AVBufferRef **buf, int size) { int ret; if (size < 0 || size >= INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE) @@ -87,7 +88,7 @@ static int packet_alloc(AVBufferRef **buf, int size) int av_new_packet(AVPacket *pkt, int size) { AVBufferRef *buf = NULL; - int ret = packet_alloc(&buf, size); + int ret = ff_buffer_padded_realloc(&buf, size); if (ret < 0) return ret; @@ -621,7 +622,7 @@ int av_packet_ref(AVPacket *dst, const AVPacket *src) goto fail; if (!src->buf) { - ret = packet_alloc(&dst->buf, src->size); + ret = ff_buffer_padded_realloc(&dst->buf, src->size); if (ret < 0) goto fail; av_assert1(!src->size || src->data); @@ -674,7 +675,7 @@ int av_packet_make_refcounted(AVPacket *pkt) if (pkt->buf) return 0; - ret = packet_alloc(&pkt->buf, pkt->size); + ret = ff_buffer_padded_realloc(&pkt->buf, pkt->size); if (ret < 0) return ret; av_assert1(!pkt->size || pkt->data); @@ -694,7 +695,7 @@ int av_packet_make_writable(AVPacket *pkt) if (pkt->buf && av_buffer_is_writable(pkt->buf)) return 0; - ret = packet_alloc(&buf, pkt->size); + ret = ff_buffer_padded_realloc(&buf, pkt->size); if (ret < 0) return ret; av_assert1(!pkt->size || pkt->data); @@ -770,3 +771,13 @@ int ff_side_data_set_prft(AVPacket *pkt, int64_t timestamp) return 0; } + +void ff_packet_replace_buffer(AVPacket *pkt, AVBufferRef *buf) +{ + av_buffer_unref(&pkt->buf); + + pkt->buf = buf; + pkt->data = buf->data; + av_assert1(buf->size >= AV_INPUT_BUFFER_PADDING_SIZE); + pkt->size = buf->size - AV_INPUT_BUFFER_PADDING_SIZE; +} diff --git a/libavcodec/bsf_internal.h b/libavcodec/bsf_internal.h index fefd5b8905..edaacaa2dd 100644 --- a/libavcodec/bsf_internal.h +++ b/libavcodec/bsf_internal.h @@ -19,6 +19,7 @@ #ifndef AVCODEC_BSF_INTERNAL_H #define AVCODEC_BSF_INTERNAL_H +#include "libavutil/buffer.h" #include "libavutil/log.h" #include "bsf.h" @@ -42,6 +43,32 @@ int ff_bsf_get_packet(AVBSFContext *ctx, AVPacket **pkt); */ int ff_bsf_get_packet_ref(AVBSFContext *ctx, AVPacket *pkt); +/** + * (Re)allocate an AVBufferRef to an effective size of size. In addition, + * the buffer will have AV_BUFFER_INPUT_PADDING_SIZE bytes of zeroed padding + * at the end. + * + * @param buf Pointer to pointer to an AVBufferRef. Must not be NULL; + * *buf will be reallocated to the desired size; if *buf is NULL, + * it will be allocated, otherwise it must be writable. + * @param size Desired usable size. + * @return Zero on success, negative error code on failure. + * *buf is unchanged on error. + */ +int ff_buffer_padded_realloc(AVBufferRef **buf, int size); + +/** + * Unreference the packet's buf and replace it with the given buf. + * The packet's data and size fields will be updated with the information + * from buf, too. + * + * @param pkt Pointer to a packet to modify. Must not be NULL. + * @param buf Pointer to an AVBufferRef. Must not be NULL. + * buf will be owned by pkt afterwards. Its size must include + * AV_INPUT_BUFFER_PADDING_SIZE bytes of padding at the end. + */ +void ff_packet_replace_buffer(AVPacket *pkt, AVBufferRef *buf); + const AVClass *ff_bsf_child_class_next(const AVClass *prev); #endif /* AVCODEC_BSF_INTERNAL_H */ -- 2.20.1 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".